/src/libbpf/src/libbpf.c

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// SPDX-License-Identifier: (LGPL-2.1 OR BSD-2-Clause)

/*
 * Common eBPF ELF object loading operations.
 *
 * Copyright (C) 2013-2015 Alexei Starovoitov <ast@kernel.org>
 * Copyright (C) 2015 Wang Nan <wangnan0@huawei.com>
 * Copyright (C) 2015 Huawei Inc.
 * Copyright (C) 2017 Nicira, Inc.
 * Copyright (C) 2019 Isovalent, Inc.
 */

#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif
#include <stdlib.h>
#include <stdio.h>
#include <stdarg.h>
#include <libgen.h>
#include <inttypes.h>
#include <limits.h>
#include <string.h>
#include <unistd.h>
#include <endian.h>
#include <fcntl.h>
#include <errno.h>
#include <ctype.h>
#include <asm/unistd.h>
#include <linux/err.h>
#include <linux/kernel.h>
#include <linux/bpf.h>
#include <linux/btf.h>
#include <linux/filter.h>
#include <linux/limits.h>
#include <linux/perf_event.h>
#include <linux/ring_buffer.h>
#include <sys/epoll.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/vfs.h>
#include <sys/utsname.h>
#include <sys/resource.h>
#include <libelf.h>
#include <gelf.h>
#include <zlib.h>

#include "libbpf.h"
#include "bpf.h"
#include "btf.h"
#include "str_error.h"
#include "libbpf_internal.h"
#include "hashmap.h"
#include "bpf_gen_internal.h"
#include "zip.h"

#ifndef BPF_FS_MAGIC
#define BPF_FS_MAGIC    0xcafe4a11
#endif

#define BPF_INSN_SZ (sizeof(struct bpf_insn))

/* vsprintf() in __base_pr() uses nonliteral format string. It may break
 * compilation if user enables corresponding warning. Disable it explicitly.
 */
#pragma GCC diagnostic ignored "-Wformat-nonliteral"

#define __printf(a, b)  __attribute__((format(printf, a, b)))

static struct bpf_map *bpf_object__add_map(struct bpf_object *obj);
static bool prog_is_subprog(const struct bpf_object *obj, const struct bpf_program *prog);

static const char * const attach_type_name[] = {
  [BPF_CGROUP_INET_INGRESS] = "cgroup_inet_ingress",
  [BPF_CGROUP_INET_EGRESS]  = "cgroup_inet_egress",
  [BPF_CGROUP_INET_SOCK_CREATE] = "cgroup_inet_sock_create",
  [BPF_CGROUP_INET_SOCK_RELEASE]  = "cgroup_inet_sock_release",
  [BPF_CGROUP_SOCK_OPS]   = "cgroup_sock_ops",
  [BPF_CGROUP_DEVICE]   = "cgroup_device",
  [BPF_CGROUP_INET4_BIND]   = "cgroup_inet4_bind",
  [BPF_CGROUP_INET6_BIND]   = "cgroup_inet6_bind",
  [BPF_CGROUP_INET4_CONNECT]  = "cgroup_inet4_connect",
  [BPF_CGROUP_INET6_CONNECT]  = "cgroup_inet6_connect",
  [BPF_CGROUP_UNIX_CONNECT]       = "cgroup_unix_connect",
  [BPF_CGROUP_INET4_POST_BIND]  = "cgroup_inet4_post_bind",
  [BPF_CGROUP_INET6_POST_BIND]  = "cgroup_inet6_post_bind",
  [BPF_CGROUP_INET4_GETPEERNAME]  = "cgroup_inet4_getpeername",
  [BPF_CGROUP_INET6_GETPEERNAME]  = "cgroup_inet6_getpeername",
  [BPF_CGROUP_UNIX_GETPEERNAME] = "cgroup_unix_getpeername",
  [BPF_CGROUP_INET4_GETSOCKNAME]  = "cgroup_inet4_getsockname",
  [BPF_CGROUP_INET6_GETSOCKNAME]  = "cgroup_inet6_getsockname",
  [BPF_CGROUP_UNIX_GETSOCKNAME] = "cgroup_unix_getsockname",
  [BPF_CGROUP_UDP4_SENDMSG] = "cgroup_udp4_sendmsg",
  [BPF_CGROUP_UDP6_SENDMSG] = "cgroup_udp6_sendmsg",
  [BPF_CGROUP_UNIX_SENDMSG] = "cgroup_unix_sendmsg",
  [BPF_CGROUP_SYSCTL]   = "cgroup_sysctl",
  [BPF_CGROUP_UDP4_RECVMSG] = "cgroup_udp4_recvmsg",
  [BPF_CGROUP_UDP6_RECVMSG] = "cgroup_udp6_recvmsg",
  [BPF_CGROUP_UNIX_RECVMSG] = "cgroup_unix_recvmsg",
  [BPF_CGROUP_GETSOCKOPT]   = "cgroup_getsockopt",
  [BPF_CGROUP_SETSOCKOPT]   = "cgroup_setsockopt",
  [BPF_SK_SKB_STREAM_PARSER]  = "sk_skb_stream_parser",
  [BPF_SK_SKB_STREAM_VERDICT] = "sk_skb_stream_verdict",
  [BPF_SK_SKB_VERDICT]    = "sk_skb_verdict",
  [BPF_SK_MSG_VERDICT]    = "sk_msg_verdict",
  [BPF_LIRC_MODE2]    = "lirc_mode2",
  [BPF_FLOW_DISSECTOR]    = "flow_dissector",
  [BPF_TRACE_RAW_TP]    = "trace_raw_tp",
  [BPF_TRACE_FENTRY]    = "trace_fentry",
  [BPF_TRACE_FEXIT]   = "trace_fexit",
  [BPF_MODIFY_RETURN]   = "modify_return",
  [BPF_LSM_MAC]     = "lsm_mac",
  [BPF_LSM_CGROUP]    = "lsm_cgroup",
  [BPF_SK_LOOKUP]     = "sk_lookup",
  [BPF_TRACE_ITER]    = "trace_iter",
  [BPF_XDP_DEVMAP]    = "xdp_devmap",
  [BPF_XDP_CPUMAP]    = "xdp_cpumap",
  [BPF_XDP]     = "xdp",
  [BPF_SK_REUSEPORT_SELECT] = "sk_reuseport_select",
  [BPF_SK_REUSEPORT_SELECT_OR_MIGRATE]  = "sk_reuseport_select_or_migrate",
  [BPF_PERF_EVENT]    = "perf_event",
  [BPF_TRACE_KPROBE_MULTI]  = "trace_kprobe_multi",
  [BPF_STRUCT_OPS]    = "struct_ops",
  [BPF_NETFILTER]     = "netfilter",
  [BPF_TCX_INGRESS]   = "tcx_ingress",
  [BPF_TCX_EGRESS]    = "tcx_egress",
  [BPF_TRACE_UPROBE_MULTI]  = "trace_uprobe_multi",
  [BPF_NETKIT_PRIMARY]    = "netkit_primary",
  [BPF_NETKIT_PEER]   = "netkit_peer",
};

static const char * const link_type_name[] = {
  [BPF_LINK_TYPE_UNSPEC]      = "unspec",
  [BPF_LINK_TYPE_RAW_TRACEPOINT]    = "raw_tracepoint",
  [BPF_LINK_TYPE_TRACING]     = "tracing",
  [BPF_LINK_TYPE_CGROUP]      = "cgroup",
  [BPF_LINK_TYPE_ITER]      = "iter",
  [BPF_LINK_TYPE_NETNS]     = "netns",
  [BPF_LINK_TYPE_XDP]     = "xdp",
  [BPF_LINK_TYPE_PERF_EVENT]    = "perf_event",
  [BPF_LINK_TYPE_KPROBE_MULTI]    = "kprobe_multi",
  [BPF_LINK_TYPE_STRUCT_OPS]    = "struct_ops",
  [BPF_LINK_TYPE_NETFILTER]   = "netfilter",
  [BPF_LINK_TYPE_TCX]     = "tcx",
  [BPF_LINK_TYPE_UPROBE_MULTI]    = "uprobe_multi",
  [BPF_LINK_TYPE_NETKIT]      = "netkit",
};

static const char * const map_type_name[] = {
  [BPF_MAP_TYPE_UNSPEC]     = "unspec",
  [BPF_MAP_TYPE_HASH]     = "hash",
  [BPF_MAP_TYPE_ARRAY]      = "array",
  [BPF_MAP_TYPE_PROG_ARRAY]   = "prog_array",
  [BPF_MAP_TYPE_PERF_EVENT_ARRAY]   = "perf_event_array",
  [BPF_MAP_TYPE_PERCPU_HASH]    = "percpu_hash",
  [BPF_MAP_TYPE_PERCPU_ARRAY]   = "percpu_array",
  [BPF_MAP_TYPE_STACK_TRACE]    = "stack_trace",
  [BPF_MAP_TYPE_CGROUP_ARRAY]   = "cgroup_array",
  [BPF_MAP_TYPE_LRU_HASH]     = "lru_hash",
  [BPF_MAP_TYPE_LRU_PERCPU_HASH]    = "lru_percpu_hash",
  [BPF_MAP_TYPE_LPM_TRIE]     = "lpm_trie",
  [BPF_MAP_TYPE_ARRAY_OF_MAPS]    = "array_of_maps",
  [BPF_MAP_TYPE_HASH_OF_MAPS]   = "hash_of_maps",
  [BPF_MAP_TYPE_DEVMAP]     = "devmap",
  [BPF_MAP_TYPE_DEVMAP_HASH]    = "devmap_hash",
  [BPF_MAP_TYPE_SOCKMAP]      = "sockmap",
  [BPF_MAP_TYPE_CPUMAP]     = "cpumap",
  [BPF_MAP_TYPE_XSKMAP]     = "xskmap",
  [BPF_MAP_TYPE_SOCKHASH]     = "sockhash",
  [BPF_MAP_TYPE_CGROUP_STORAGE]   = "cgroup_storage",
  [BPF_MAP_TYPE_REUSEPORT_SOCKARRAY]  = "reuseport_sockarray",
  [BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE]  = "percpu_cgroup_storage",
  [BPF_MAP_TYPE_QUEUE]      = "queue",
  [BPF_MAP_TYPE_STACK]      = "stack",
  [BPF_MAP_TYPE_SK_STORAGE]   = "sk_storage",
  [BPF_MAP_TYPE_STRUCT_OPS]   = "struct_ops",
  [BPF_MAP_TYPE_RINGBUF]      = "ringbuf",
  [BPF_MAP_TYPE_INODE_STORAGE]    = "inode_storage",
  [BPF_MAP_TYPE_TASK_STORAGE]   = "task_storage",
  [BPF_MAP_TYPE_BLOOM_FILTER]   = "bloom_filter",
  [BPF_MAP_TYPE_USER_RINGBUF]             = "user_ringbuf",
  [BPF_MAP_TYPE_CGRP_STORAGE]   = "cgrp_storage",
};

static const char * const prog_type_name[] = {
  [BPF_PROG_TYPE_UNSPEC]      = "unspec",
  [BPF_PROG_TYPE_SOCKET_FILTER]   = "socket_filter",
  [BPF_PROG_TYPE_KPROBE]      = "kprobe",
  [BPF_PROG_TYPE_SCHED_CLS]   = "sched_cls",
  [BPF_PROG_TYPE_SCHED_ACT]   = "sched_act",
  [BPF_PROG_TYPE_TRACEPOINT]    = "tracepoint",
  [BPF_PROG_TYPE_XDP]     = "xdp",
  [BPF_PROG_TYPE_PERF_EVENT]    = "perf_event",
  [BPF_PROG_TYPE_CGROUP_SKB]    = "cgroup_skb",
  [BPF_PROG_TYPE_CGROUP_SOCK]   = "cgroup_sock",
  [BPF_PROG_TYPE_LWT_IN]      = "lwt_in",
  [BPF_PROG_TYPE_LWT_OUT]     = "lwt_out",
  [BPF_PROG_TYPE_LWT_XMIT]    = "lwt_xmit",
  [BPF_PROG_TYPE_SOCK_OPS]    = "sock_ops",
  [BPF_PROG_TYPE_SK_SKB]      = "sk_skb",
  [BPF_PROG_TYPE_CGROUP_DEVICE]   = "cgroup_device",
  [BPF_PROG_TYPE_SK_MSG]      = "sk_msg",
  [BPF_PROG_TYPE_RAW_TRACEPOINT]    = "raw_tracepoint",
  [BPF_PROG_TYPE_CGROUP_SOCK_ADDR]  = "cgroup_sock_addr",
  [BPF_PROG_TYPE_LWT_SEG6LOCAL]   = "lwt_seg6local",
  [BPF_PROG_TYPE_LIRC_MODE2]    = "lirc_mode2",
  [BPF_PROG_TYPE_SK_REUSEPORT]    = "sk_reuseport",
  [BPF_PROG_TYPE_FLOW_DISSECTOR]    = "flow_dissector",
  [BPF_PROG_TYPE_CGROUP_SYSCTL]   = "cgroup_sysctl",
  [BPF_PROG_TYPE_RAW_TRACEPOINT_WRITABLE] = "raw_tracepoint_writable",
  [BPF_PROG_TYPE_CGROUP_SOCKOPT]    = "cgroup_sockopt",
  [BPF_PROG_TYPE_TRACING]     = "tracing",
  [BPF_PROG_TYPE_STRUCT_OPS]    = "struct_ops",
  [BPF_PROG_TYPE_EXT]     = "ext",
  [BPF_PROG_TYPE_LSM]     = "lsm",
  [BPF_PROG_TYPE_SK_LOOKUP]   = "sk_lookup",
  [BPF_PROG_TYPE_SYSCALL]     = "syscall",
  [BPF_PROG_TYPE_NETFILTER]   = "netfilter",
};

static int __base_pr(enum libbpf_print_level level, const char *format,
         va_list args)
{
  if (level == LIBBPF_DEBUG)
    return 0;

  return vfprintf(stderr, format, args);
}

static libbpf_print_fn_t __libbpf_pr = __base_pr;

libbpf_print_fn_t libbpf_set_print(libbpf_print_fn_t fn)
{
  libbpf_print_fn_t old_print_fn;

  old_print_fn = __atomic_exchange_n(&__libbpf_pr, fn, __ATOMIC_RELAXED);

  return old_print_fn;
}

__printf(2, 3)
void libbpf_print(enum libbpf_print_level level, const char *format, ...)
{
  va_list args;
  int old_errno;
  libbpf_print_fn_t print_fn;

  print_fn = __atomic_load_n(&__libbpf_pr, __ATOMIC_RELAXED);
  if (!print_fn)
    return;

  old_errno = errno;

  va_start(args, format);
  __libbpf_pr(level, format, args);
  va_end(args);

  errno = old_errno;
}

static void pr_perm_msg(int err)
{
  struct rlimit limit;
  char buf[100];

  if (err != -EPERM || geteuid() != 0)
    return;

  err = getrlimit(RLIMIT_MEMLOCK, &limit);
  if (err)
    return;

  if (limit.rlim_cur == RLIM_INFINITY)
    return;

  if (limit.rlim_cur < 1024)
    snprintf(buf, sizeof(buf), "%zu bytes", (size_t)limit.rlim_cur);
  else if (limit.rlim_cur < 1024*1024)
    snprintf(buf, sizeof(buf), "%.1f KiB", (double)limit.rlim_cur / 1024);
  else
    snprintf(buf, sizeof(buf), "%.1f MiB", (double)limit.rlim_cur / (1024*1024));

  pr_warn("permission error while running as root; try raising 'ulimit -l'? current value: %s\n",
    buf);
}

#define STRERR_BUFSIZE  128

/* Copied from tools/perf/util/util.h */
#ifndef zfree
# define zfree(ptr) ({ free(*ptr); *ptr = NULL; })
#endif

#ifndef zclose
# define zclose(fd) ({      \
  int ___err = 0;     \
  if ((fd) >= 0)     \
    ___err = close((fd)); \
  fd = -1;      \
  ___err; })
#endif

static inline __u64 ptr_to_u64(const void *ptr)
{
  return (__u64) (unsigned long) ptr;
}

int libbpf_set_strict_mode(enum libbpf_strict_mode mode)
{
  /* as of v1.0 libbpf_set_strict_mode() is a no-op */
  return 0;
}

__u32 libbpf_major_version(void)
{
  return LIBBPF_MAJOR_VERSION;
}

__u32 libbpf_minor_version(void)
{
  return LIBBPF_MINOR_VERSION;
}

const char *libbpf_version_string(void)
{
#define __S(X) #X
#define _S(X) __S(X)
  return  "v" _S(LIBBPF_MAJOR_VERSION) "." _S(LIBBPF_MINOR_VERSION);
#undef _S
#undef __S
}

enum reloc_type {
  RELO_LD64,
  RELO_CALL,
  RELO_DATA,
  RELO_EXTERN_LD64,
  RELO_EXTERN_CALL,
  RELO_SUBPROG_ADDR,
  RELO_CORE,
};

struct reloc_desc {
  enum reloc_type type;
  int insn_idx;
  union {
    const struct bpf_core_relo *core_relo; /* used when type == RELO_CORE */
    struct {
      int map_idx;
      int sym_off;
      int ext_idx;
    };
  };
};

/* stored as sec_def->cookie for all libbpf-supported SEC()s */
enum sec_def_flags {
  SEC_NONE = 0,
  /* expected_attach_type is optional, if kernel doesn't support that */
  SEC_EXP_ATTACH_OPT = 1,
  /* legacy, only used by libbpf_get_type_names() and
   * libbpf_attach_type_by_name(), not used by libbpf itself at all.
   * This used to be associated with cgroup (and few other) BPF programs
   * that were attachable through BPF_PROG_ATTACH command. Pretty
   * meaningless nowadays, though.
   */
  SEC_ATTACHABLE = 2,
  SEC_ATTACHABLE_OPT = SEC_ATTACHABLE | SEC_EXP_ATTACH_OPT,
  /* attachment target is specified through BTF ID in either kernel or
   * other BPF program's BTF object
   */
  SEC_ATTACH_BTF = 4,
  /* BPF program type allows sleeping/blocking in kernel */
  SEC_SLEEPABLE = 8,
  /* BPF program support non-linear XDP buffer */
  SEC_XDP_FRAGS = 16,
  /* Setup proper attach type for usdt probes. */
  SEC_USDT = 32,
};

struct bpf_sec_def {
  char *sec;
  enum bpf_prog_type prog_type;
  enum bpf_attach_type expected_attach_type;
  long cookie;
  int handler_id;

  libbpf_prog_setup_fn_t prog_setup_fn;
  libbpf_prog_prepare_load_fn_t prog_prepare_load_fn;
  libbpf_prog_attach_fn_t prog_attach_fn;
};

/*
 * bpf_prog should be a better name but it has been used in
 * linux/filter.h.
 */
struct bpf_program {
  char *name;
  char *sec_name;
  size_t sec_idx;
  const struct bpf_sec_def *sec_def;
  /* this program's instruction offset (in number of instructions)
   * within its containing ELF section
   */
  size_t sec_insn_off;
  /* number of original instructions in ELF section belonging to this
   * program, not taking into account subprogram instructions possible
   * appended later during relocation
   */
  size_t sec_insn_cnt;
  /* Offset (in number of instructions) of the start of instruction
   * belonging to this BPF program  within its containing main BPF
   * program. For the entry-point (main) BPF program, this is always
   * zero. For a sub-program, this gets reset before each of main BPF
   * programs are processed and relocated and is used to determined
   * whether sub-program was already appended to the main program, and
   * if yes, at which instruction offset.
   */
  size_t sub_insn_off;

  /* instructions that belong to BPF program; insns[0] is located at
   * sec_insn_off instruction within its ELF section in ELF file, so
   * when mapping ELF file instruction index to the local instruction,
   * one needs to subtract sec_insn_off; and vice versa.
   */
  struct bpf_insn *insns;
  /* actual number of instruction in this BPF program's image; for
   * entry-point BPF programs this includes the size of main program
   * itself plus all the used sub-programs, appended at the end
   */
  size_t insns_cnt;

  struct reloc_desc *reloc_desc;
  int nr_reloc;

  /* BPF verifier log settings */
  char *log_buf;
  size_t log_size;
  __u32 log_level;

  struct bpf_object *obj;

  int fd;
  bool autoload;
  bool autoattach;
  bool sym_global;
  bool mark_btf_static;
  enum bpf_prog_type type;
  enum bpf_attach_type expected_attach_type;
  int exception_cb_idx;

  int prog_ifindex;
  __u32 attach_btf_obj_fd;
  __u32 attach_btf_id;
  __u32 attach_prog_fd;

  void *func_info;
  __u32 func_info_rec_size;
  __u32 func_info_cnt;

  void *line_info;
  __u32 line_info_rec_size;
  __u32 line_info_cnt;
  __u32 prog_flags;
};

struct bpf_struct_ops {
  const char *tname;
  const struct btf_type *type;
  struct bpf_program **progs;
  __u32 *kern_func_off;
  /* e.g. struct tcp_congestion_ops in bpf_prog's btf format */
  void *data;
  /* e.g. struct bpf_struct_ops_tcp_congestion_ops in
   *      btf_vmlinux's format.
   * struct bpf_struct_ops_tcp_congestion_ops {
   *  [... some other kernel fields ...]
   *  struct tcp_congestion_ops data;
   * }
   * kern_vdata-size == sizeof(struct bpf_struct_ops_tcp_congestion_ops)
   * bpf_map__init_kern_struct_ops() will populate the "kern_vdata"
   * from "data".
   */
  void *kern_vdata;
  __u32 type_id;
};

#define DATA_SEC ".data"
#define BSS_SEC ".bss"
#define RODATA_SEC ".rodata"
#define KCONFIG_SEC ".kconfig"
#define KSYMS_SEC ".ksyms"
#define STRUCT_OPS_SEC ".struct_ops"
#define STRUCT_OPS_LINK_SEC ".struct_ops.link"

enum libbpf_map_type {
  LIBBPF_MAP_UNSPEC,
  LIBBPF_MAP_DATA,
  LIBBPF_MAP_BSS,
  LIBBPF_MAP_RODATA,
  LIBBPF_MAP_KCONFIG,
};

struct bpf_map_def {
  unsigned int type;
  unsigned int key_size;
  unsigned int value_size;
  unsigned int max_entries;
  unsigned int map_flags;
};

struct bpf_map {
  struct bpf_object *obj;
  char *name;
  /* real_name is defined for special internal maps (.rodata*,
   * .data*, .bss, .kconfig) and preserves their original ELF section
   * name. This is important to be able to find corresponding BTF
   * DATASEC information.
   */
  char *real_name;
  int fd;
  int sec_idx;
  size_t sec_offset;
  int map_ifindex;
  int inner_map_fd;
  struct bpf_map_def def;
  __u32 numa_node;
  __u32 btf_var_idx;
  __u32 btf_key_type_id;
  __u32 btf_value_type_id;
  __u32 btf_vmlinux_value_type_id;
  enum libbpf_map_type libbpf_type;
  void *mmaped;
  struct bpf_struct_ops *st_ops;
  struct bpf_map *inner_map;
  void **init_slots;
  int init_slots_sz;
  char *pin_path;
  bool pinned;
  bool reused;
  bool autocreate;
  __u64 map_extra;
};

enum extern_type {
  EXT_UNKNOWN,
  EXT_KCFG,
  EXT_KSYM,
};

enum kcfg_type {
  KCFG_UNKNOWN,
  KCFG_CHAR,
  KCFG_BOOL,
  KCFG_INT,
  KCFG_TRISTATE,
  KCFG_CHAR_ARR,
};

struct extern_desc {
  enum extern_type type;
  int sym_idx;
  int btf_id;
  int sec_btf_id;
  const char *name;
  char *essent_name;
  bool is_set;
  bool is_weak;
  union {
    struct {
      enum kcfg_type type;
      int sz;
      int align;
      int data_off;
      bool is_signed;
    } kcfg;
    struct {
      unsigned long long addr;

      /* target btf_id of the corresponding kernel var. */
      int kernel_btf_obj_fd;
      int kernel_btf_id;

      /* local btf_id of the ksym extern's type. */
      __u32 type_id;
      /* BTF fd index to be patched in for insn->off, this is
       * 0 for vmlinux BTF, index in obj->fd_array for module
       * BTF
       */
      __s16 btf_fd_idx;
    } ksym;
  };
};

struct module_btf {
  struct btf *btf;
  char *name;
  __u32 id;
  int fd;
  int fd_array_idx;
};

enum sec_type {
  SEC_UNUSED = 0,
  SEC_RELO,
  SEC_BSS,
  SEC_DATA,
  SEC_RODATA,
};

struct elf_sec_desc {
  enum sec_type sec_type;
  Elf64_Shdr *shdr;
  Elf_Data *data;
};

struct elf_state {
  int fd;
  const void *obj_buf;
  size_t obj_buf_sz;
  Elf *elf;
  Elf64_Ehdr *ehdr;
  Elf_Data *symbols;
  Elf_Data *st_ops_data;
  Elf_Data *st_ops_link_data;
  size_t shstrndx; /* section index for section name strings */
  size_t strtabidx;
  struct elf_sec_desc *secs;
  size_t sec_cnt;
  int btf_maps_shndx;
  __u32 btf_maps_sec_btf_id;
  int text_shndx;
  int symbols_shndx;
  int st_ops_shndx;
  int st_ops_link_shndx;
};

struct usdt_manager;

struct bpf_object {
  char name[BPF_OBJ_NAME_LEN];
  char license[64];
  __u32 kern_version;

  struct bpf_program *programs;
  size_t nr_programs;
  struct bpf_map *maps;
  size_t nr_maps;
  size_t maps_cap;

  char *kconfig;
  struct extern_desc *externs;
  int nr_extern;
  int kconfig_map_idx;

  bool loaded;
  bool has_subcalls;
  bool has_rodata;

  struct bpf_gen *gen_loader;

  /* Information when doing ELF related work. Only valid if efile.elf is not NULL */
  struct elf_state efile;

  struct btf *btf;
  struct btf_ext *btf_ext;

  /* Parse and load BTF vmlinux if any of the programs in the object need
   * it at load time.
   */
  struct btf *btf_vmlinux;
  /* Path to the custom BTF to be used for BPF CO-RE relocations as an
   * override for vmlinux BTF.
   */
  char *btf_custom_path;
  /* vmlinux BTF override for CO-RE relocations */
  struct btf *btf_vmlinux_override;
  /* Lazily initialized kernel module BTFs */
  struct module_btf *btf_modules;
  bool btf_modules_loaded;
  size_t btf_module_cnt;
  size_t btf_module_cap;

  /* optional log settings passed to BPF_BTF_LOAD and BPF_PROG_LOAD commands */
  char *log_buf;
  size_t log_size;
  __u32 log_level;

  int *fd_array;
  size_t fd_array_cap;
  size_t fd_array_cnt;

  struct usdt_manager *usdt_man;

  char path[];
};

static const char *elf_sym_str(const struct bpf_object *obj, size_t off);
static const char *elf_sec_str(const struct bpf_object *obj, size_t off);
static Elf_Scn *elf_sec_by_idx(const struct bpf_object *obj, size_t idx);
static Elf_Scn *elf_sec_by_name(const struct bpf_object *obj, const char *name);
static Elf64_Shdr *elf_sec_hdr(const struct bpf_object *obj, Elf_Scn *scn);
static const char *elf_sec_name(const struct bpf_object *obj, Elf_Scn *scn);
static Elf_Data *elf_sec_data(const struct bpf_object *obj, Elf_Scn *scn);
static Elf64_Sym *elf_sym_by_idx(const struct bpf_object *obj, size_t idx);
static Elf64_Rel *elf_rel_by_idx(Elf_Data *data, size_t idx);

void bpf_program__unload(struct bpf_program *prog)
{
  if (!prog)
    return;

  zclose(prog->fd);

  zfree(&prog->func_info);
  zfree(&prog->line_info);
}

static void bpf_program__exit(struct bpf_program *prog)
{
  if (!prog)
    return;

  bpf_program__unload(prog);
  zfree(&prog->name);
  zfree(&prog->sec_name);
  zfree(&prog->insns);
  zfree(&prog->reloc_desc);

  prog->nr_reloc = 0;
  prog->insns_cnt = 0;
  prog->sec_idx = -1;
}

static bool insn_is_subprog_call(const struct bpf_insn *insn)
{
  return BPF_CLASS(insn->code) == BPF_JMP &&
         BPF_OP(insn->code) == BPF_CALL &&
         BPF_SRC(insn->code) == BPF_K &&
         insn->src_reg == BPF_PSEUDO_CALL &&
         insn->dst_reg == 0 &&
         insn->off == 0;
}

static bool is_call_insn(const struct bpf_insn *insn)
{
  return insn->code == (BPF_JMP | BPF_CALL);
}

static bool insn_is_pseudo_func(struct bpf_insn *insn)
{
  return is_ldimm64_insn(insn) && insn->src_reg == BPF_PSEUDO_FUNC;
}

static int
bpf_object__init_prog(struct bpf_object *obj, struct bpf_program *prog,
          const char *name, size_t sec_idx, const char *sec_name,
          size_t sec_off, void *insn_data, size_t insn_data_sz)
{
  if (insn_data_sz == 0 || insn_data_sz % BPF_INSN_SZ || sec_off % BPF_INSN_SZ) {
    pr_warn("sec '%s': corrupted program '%s', offset %zu, size %zu\n",
      sec_name, name, sec_off, insn_data_sz);
    return -EINVAL;
  }

  memset(prog, 0, sizeof(*prog));
  prog->obj = obj;

  prog->sec_idx = sec_idx;
  prog->sec_insn_off = sec_off / BPF_INSN_SZ;
  prog->sec_insn_cnt = insn_data_sz / BPF_INSN_SZ;
  /* insns_cnt can later be increased by appending used subprograms */
  prog->insns_cnt = prog->sec_insn_cnt;

  prog->type = BPF_PROG_TYPE_UNSPEC;
  prog->fd = -1;
  prog->exception_cb_idx = -1;

  /* libbpf's convention for SEC("?abc...") is that it's just like
   * SEC("abc...") but the corresponding bpf_program starts out with
   * autoload set to false.
   */
  if (sec_name[0] == '?') {
    prog->autoload = false;
    /* from now on forget there was ? in section name */
    sec_name++;
  } else {
    prog->autoload = true;
  }

  prog->autoattach = true;

  /* inherit object's log_level */
  prog->log_level = obj->log_level;

  prog->sec_name = strdup(sec_name);
  if (!prog->sec_name)
    goto errout;

  prog->name = strdup(name);
  if (!prog->name)
    goto errout;

  prog->insns = malloc(insn_data_sz);
  if (!prog->insns)
    goto errout;
  memcpy(prog->insns, insn_data, insn_data_sz);

  return 0;
errout:
  pr_warn("sec '%s': failed to allocate memory for prog '%s'\n", sec_name, name);
  bpf_program__exit(prog);
  return -ENOMEM;
}

static int
bpf_object__add_programs(struct bpf_object *obj, Elf_Data *sec_data,
       const char *sec_name, int sec_idx)
{
  Elf_Data *symbols = obj->efile.symbols;
  struct bpf_program *prog, *progs;
  void *data = sec_data->d_buf;
  size_t sec_sz = sec_data->d_size, sec_off, prog_sz, nr_syms;
  int nr_progs, err, i;
  const char *name;
  Elf64_Sym *sym;

  progs = obj->programs;
  nr_progs = obj->nr_programs;
  nr_syms = symbols->d_size / sizeof(Elf64_Sym);

  for (i = 0; i < nr_syms; i++) {
    sym = elf_sym_by_idx(obj, i);

    if (sym->st_shndx != sec_idx)
      continue;
    if (ELF64_ST_TYPE(sym->st_info) != STT_FUNC)
      continue;

    prog_sz = sym->st_size;
    sec_off = sym->st_value;

    name = elf_sym_str(obj, sym->st_name);
    if (!name) {
      pr_warn("sec '%s': failed to get symbol name for offset %zu\n",
        sec_name, sec_off);
      return -LIBBPF_ERRNO__FORMAT;
    }

    if (sec_off + prog_sz > sec_sz) {
      pr_warn("sec '%s': program at offset %zu crosses section boundary\n",
        sec_name, sec_off);
      return -LIBBPF_ERRNO__FORMAT;
    }

    if (sec_idx != obj->efile.text_shndx && ELF64_ST_BIND(sym->st_info) == STB_LOCAL) {
      pr_warn("sec '%s': program '%s' is static and not supported\n", sec_name, name);
      return -ENOTSUP;
    }

    pr_debug("sec '%s': found program '%s' at insn offset %zu (%zu bytes), code size %zu insns (%zu bytes)\n",
       sec_name, name, sec_off / BPF_INSN_SZ, sec_off, prog_sz / BPF_INSN_SZ, prog_sz);

    progs = libbpf_reallocarray(progs, nr_progs + 1, sizeof(*progs));
    if (!progs) {
      /*
       * In this case the original obj->programs
       * is still valid, so don't need special treat for
       * bpf_close_object().
       */
      pr_warn("sec '%s': failed to alloc memory for new program '%s'\n",
        sec_name, name);
      return -ENOMEM;
    }
    obj->programs = progs;

    prog = &progs[nr_progs];

    err = bpf_object__init_prog(obj, prog, name, sec_idx, sec_name,
              sec_off, data + sec_off, prog_sz);
    if (err)
      return err;

    if (ELF64_ST_BIND(sym->st_info) != STB_LOCAL)
      prog->sym_global = true;

    /* if function is a global/weak symbol, but has restricted
     * (STV_HIDDEN or STV_INTERNAL) visibility, mark its BTF FUNC
     * as static to enable more permissive BPF verification mode
     * with more outside context available to BPF verifier
     */
    if (prog->sym_global && (ELF64_ST_VISIBILITY(sym->st_other) == STV_HIDDEN
        || ELF64_ST_VISIBILITY(sym->st_other) == STV_INTERNAL))
      prog->mark_btf_static = true;

    nr_progs++;
    obj->nr_programs = nr_progs;
  }

  return 0;
}

static const struct btf_member *
find_member_by_offset(const struct btf_type *t, __u32 bit_offset)
{
  struct btf_member *m;
  int i;

  for (i = 0, m = btf_members(t); i < btf_vlen(t); i++, m++) {
    if (btf_member_bit_offset(t, i) == bit_offset)
      return m;
  }

  return NULL;
}

static const struct btf_member *
find_member_by_name(const struct btf *btf, const struct btf_type *t,
        const char *name)
{
  struct btf_member *m;
  int i;

  for (i = 0, m = btf_members(t); i < btf_vlen(t); i++, m++) {
    if (!strcmp(btf__name_by_offset(btf, m->name_off), name))
      return m;
  }

  return NULL;
}

#define STRUCT_OPS_VALUE_PREFIX "bpf_struct_ops_"
static int find_btf_by_prefix_kind(const struct btf *btf, const char *prefix,
           const char *name, __u32 kind);

static int
find_struct_ops_kern_types(const struct btf *btf, const char *tname,
         const struct btf_type **type, __u32 *type_id,
         const struct btf_type **vtype, __u32 *vtype_id,
         const struct btf_member **data_member)
{
  const struct btf_type *kern_type, *kern_vtype;
  const struct btf_member *kern_data_member;
  __s32 kern_vtype_id, kern_type_id;
  __u32 i;

  kern_type_id = btf__find_by_name_kind(btf, tname, BTF_KIND_STRUCT);
  if (kern_type_id < 0) {
    pr_warn("struct_ops init_kern: struct %s is not found in kernel BTF\n",
      tname);
    return kern_type_id;
  }
  kern_type = btf__type_by_id(btf, kern_type_id);

  /* Find the corresponding "map_value" type that will be used
   * in map_update(BPF_MAP_TYPE_STRUCT_OPS).  For example,
   * find "struct bpf_struct_ops_tcp_congestion_ops" from the
   * btf_vmlinux.
   */
  kern_vtype_id = find_btf_by_prefix_kind(btf, STRUCT_OPS_VALUE_PREFIX,
            tname, BTF_KIND_STRUCT);
  if (kern_vtype_id < 0) {
    pr_warn("struct_ops init_kern: struct %s%s is not found in kernel BTF\n",
      STRUCT_OPS_VALUE_PREFIX, tname);
    return kern_vtype_id;
  }
  kern_vtype = btf__type_by_id(btf, kern_vtype_id);

  /* Find "struct tcp_congestion_ops" from
   * struct bpf_struct_ops_tcp_congestion_ops {
   *  [ ... ]
   *  struct tcp_congestion_ops data;
   * }
   */
  kern_data_member = btf_members(kern_vtype);
  for (i = 0; i < btf_vlen(kern_vtype); i++, kern_data_member++) {
    if (kern_data_member->type == kern_type_id)
      break;
  }
  if (i == btf_vlen(kern_vtype)) {
    pr_warn("struct_ops init_kern: struct %s data is not found in struct %s%s\n",
      tname, STRUCT_OPS_VALUE_PREFIX, tname);
    return -EINVAL;
  }

  *type = kern_type;
  *type_id = kern_type_id;
  *vtype = kern_vtype;
  *vtype_id = kern_vtype_id;
  *data_member = kern_data_member;

  return 0;
}

static bool bpf_map__is_struct_ops(const struct bpf_map *map)
{
  return map->def.type == BPF_MAP_TYPE_STRUCT_OPS;
}

/* Init the map's fields that depend on kern_btf */
static int bpf_map__init_kern_struct_ops(struct bpf_map *map,
           const struct btf *btf,
           const struct btf *kern_btf)
{
  const struct btf_member *member, *kern_member, *kern_data_member;
  const struct btf_type *type, *kern_type, *kern_vtype;
  __u32 i, kern_type_id, kern_vtype_id, kern_data_off;
  struct bpf_struct_ops *st_ops;
  void *data, *kern_data;
  const char *tname;
  int err;

  st_ops = map->st_ops;
  type = st_ops->type;
  tname = st_ops->tname;
  err = find_struct_ops_kern_types(kern_btf, tname,
           &kern_type, &kern_type_id,
           &kern_vtype, &kern_vtype_id,
           &kern_data_member);
  if (err)
    return err;

  pr_debug("struct_ops init_kern %s: type_id:%u kern_type_id:%u kern_vtype_id:%u\n",
     map->name, st_ops->type_id, kern_type_id, kern_vtype_id);

  map->def.value_size = kern_vtype->size;
  map->btf_vmlinux_value_type_id = kern_vtype_id;

  st_ops->kern_vdata = calloc(1, kern_vtype->size);
  if (!st_ops->kern_vdata)
    return -ENOMEM;

  data = st_ops->data;
  kern_data_off = kern_data_member->offset / 8;
  kern_data = st_ops->kern_vdata + kern_data_off;

  member = btf_members(type);
  for (i = 0; i < btf_vlen(type); i++, member++) {
    const struct btf_type *mtype, *kern_mtype;
    __u32 mtype_id, kern_mtype_id;
    void *mdata, *kern_mdata;
    __s64 msize, kern_msize;
    __u32 moff, kern_moff;
    __u32 kern_member_idx;
    const char *mname;

    mname = btf__name_by_offset(btf, member->name_off);
    kern_member = find_member_by_name(kern_btf, kern_type, mname);
    if (!kern_member) {
      pr_warn("struct_ops init_kern %s: Cannot find member %s in kernel BTF\n",
        map->name, mname);
      return -ENOTSUP;
    }

    kern_member_idx = kern_member - btf_members(kern_type);
    if (btf_member_bitfield_size(type, i) ||
        btf_member_bitfield_size(kern_type, kern_member_idx)) {
      pr_warn("struct_ops init_kern %s: bitfield %s is not supported\n",
        map->name, mname);
      return -ENOTSUP;
    }

    moff = member->offset / 8;
    kern_moff = kern_member->offset / 8;

    mdata = data + moff;
    kern_mdata = kern_data + kern_moff;

    mtype = skip_mods_and_typedefs(btf, member->type, &mtype_id);
    kern_mtype = skip_mods_and_typedefs(kern_btf, kern_member->type,
                &kern_mtype_id);
    if (BTF_INFO_KIND(mtype->info) !=
        BTF_INFO_KIND(kern_mtype->info)) {
      pr_warn("struct_ops init_kern %s: Unmatched member type %s %u != %u(kernel)\n",
        map->name, mname, BTF_INFO_KIND(mtype->info),
        BTF_INFO_KIND(kern_mtype->info));
      return -ENOTSUP;
    }

    if (btf_is_ptr(mtype)) {
      struct bpf_program *prog;

      prog = st_ops->progs[i];
      if (!prog)
        continue;

      kern_mtype = skip_mods_and_typedefs(kern_btf,
                  kern_mtype->type,
                  &kern_mtype_id);

      /* mtype->type must be a func_proto which was
       * guaranteed in bpf_object__collect_st_ops_relos(),
       * so only check kern_mtype for func_proto here.
       */
      if (!btf_is_func_proto(kern_mtype)) {
        pr_warn("struct_ops init_kern %s: kernel member %s is not a func ptr\n",
          map->name, mname);
        return -ENOTSUP;
      }

      prog->attach_btf_id = kern_type_id;
      prog->expected_attach_type = kern_member_idx;

      st_ops->kern_func_off[i] = kern_data_off + kern_moff;

      pr_debug("struct_ops init_kern %s: func ptr %s is set to prog %s from data(+%u) to kern_data(+%u)\n",
         map->name, mname, prog->name, moff,
         kern_moff);

      continue;
    }

    msize = btf__resolve_size(btf, mtype_id);
    kern_msize = btf__resolve_size(kern_btf, kern_mtype_id);
    if (msize < 0 || kern_msize < 0 || msize != kern_msize) {
      pr_warn("struct_ops init_kern %s: Error in size of member %s: %zd != %zd(kernel)\n",
        map->name, mname, (ssize_t)msize,
        (ssize_t)kern_msize);
      return -ENOTSUP;
    }

    pr_debug("struct_ops init_kern %s: copy %s %u bytes from data(+%u) to kern_data(+%u)\n",
       map->name, mname, (unsigned int)msize,
       moff, kern_moff);
    memcpy(kern_mdata, mdata, msize);
  }

  return 0;
}

static int bpf_object__init_kern_struct_ops_maps(struct bpf_object *obj)
{
  struct bpf_map *map;
  size_t i;
  int err;

  for (i = 0; i < obj->nr_maps; i++) {
    map = &obj->maps[i];

    if (!bpf_map__is_struct_ops(map))
      continue;

    err = bpf_map__init_kern_struct_ops(map, obj->btf,
                obj->btf_vmlinux);
    if (err)
      return err;
  }

  return 0;
}

static int init_struct_ops_maps(struct bpf_object *obj, const char *sec_name,
        int shndx, Elf_Data *data, __u32 map_flags)
{
  const struct btf_type *type, *datasec;
  const struct btf_var_secinfo *vsi;
  struct bpf_struct_ops *st_ops;
  const char *tname, *var_name;
  __s32 type_id, datasec_id;
  const struct btf *btf;
  struct bpf_map *map;
  __u32 i;

  if (shndx == -1)
    return 0;

  btf = obj->btf;
  datasec_id = btf__find_by_name_kind(btf, sec_name,
              BTF_KIND_DATASEC);
  if (datasec_id < 0) {
    pr_warn("struct_ops init: DATASEC %s not found\n",
      sec_name);
    return -EINVAL;
  }

  datasec = btf__type_by_id(btf, datasec_id);
  vsi = btf_var_secinfos(datasec);
  for (i = 0; i < btf_vlen(datasec); i++, vsi++) {
    type = btf__type_by_id(obj->btf, vsi->type);
    var_name = btf__name_by_offset(obj->btf, type->name_off);

    type_id = btf__resolve_type(obj->btf, vsi->type);
    if (type_id < 0) {
      pr_warn("struct_ops init: Cannot resolve var type_id %u in DATASEC %s\n",
        vsi->type, sec_name);
      return -EINVAL;
    }

    type = btf__type_by_id(obj->btf, type_id);
    tname = btf__name_by_offset(obj->btf, type->name_off);
    if (!tname[0]) {
      pr_warn("struct_ops init: anonymous type is not supported\n");
      return -ENOTSUP;
    }
    if (!btf_is_struct(type)) {
      pr_warn("struct_ops init: %s is not a struct\n", tname);
      return -EINVAL;
    }

    map = bpf_object__add_map(obj);
    if (IS_ERR(map))
      return PTR_ERR(map);

    map->sec_idx = shndx;
    map->sec_offset = vsi->offset;
    map->name = strdup(var_name);
    if (!map->name)
      return -ENOMEM;

    map->def.type = BPF_MAP_TYPE_STRUCT_OPS;
    map->def.key_size = sizeof(int);
    map->def.value_size = type->size;
    map->def.max_entries = 1;
    map->def.map_flags = map_flags;

    map->st_ops = calloc(1, sizeof(*map->st_ops));
    if (!map->st_ops)
      return -ENOMEM;
    st_ops = map->st_ops;
    st_ops->data = malloc(type->size);
    st_ops->progs = calloc(btf_vlen(type), sizeof(*st_ops->progs));
    st_ops->kern_func_off = malloc(btf_vlen(type) *
                 sizeof(*st_ops->kern_func_off));
    if (!st_ops->data || !st_ops->progs || !st_ops->kern_func_off)
      return -ENOMEM;

    if (vsi->offset + type->size > data->d_size) {
      pr_warn("struct_ops init: var %s is beyond the end of DATASEC %s\n",
        var_name, sec_name);
      return -EINVAL;
    }

    memcpy(st_ops->data,
           data->d_buf + vsi->offset,
           type->size);
    st_ops->tname = tname;
    st_ops->type = type;
    st_ops->type_id = type_id;

    pr_debug("struct_ops init: struct %s(type_id=%u) %s found at offset %u\n",
       tname, type_id, var_name, vsi->offset);
  }

  return 0;
}

static int bpf_object_init_struct_ops(struct bpf_object *obj)
{
  int err;

  err = init_struct_ops_maps(obj, STRUCT_OPS_SEC, obj->efile.st_ops_shndx,
           obj->efile.st_ops_data, 0);
  err = err ?: init_struct_ops_maps(obj, STRUCT_OPS_LINK_SEC,
            obj->efile.st_ops_link_shndx,
            obj->efile.st_ops_link_data,
            BPF_F_LINK);
  return err;
}

static struct bpf_object *bpf_object__new(const char *path,
            const void *obj_buf,
            size_t obj_buf_sz,
            const char *obj_name)
{
  struct bpf_object *obj;
  char *end;

  obj = calloc(1, sizeof(struct bpf_object) + strlen(path) + 1);
  if (!obj) {
    pr_warn("alloc memory failed for %s\n", path);
    return ERR_PTR(-ENOMEM);
  }

  strcpy(obj->path, path);
  if (obj_name) {
    libbpf_strlcpy(obj->name, obj_name, sizeof(obj->name));
  } else {
    /* Using basename() GNU version which doesn't modify arg. */
    libbpf_strlcpy(obj->name, basename((void *)path), sizeof(obj->name));
    end = strchr(obj->name, '.');
    if (end)
      *end = 0;
  }

  obj->efile.fd = -1;
  /*
   * Caller of this function should also call
   * bpf_object__elf_finish() after data collection to return
   * obj_buf to user. If not, we should duplicate the buffer to
   * avoid user freeing them before elf finish.
   */
  obj->efile.obj_buf = obj_buf;
  obj->efile.obj_buf_sz = obj_buf_sz;
  obj->efile.btf_maps_shndx = -1;
  obj->efile.st_ops_shndx = -1;
  obj->efile.st_ops_link_shndx = -1;
  obj->kconfig_map_idx = -1;

  obj->kern_version = get_kernel_version();
  obj->loaded = false;

  return obj;
}

static void bpf_object__elf_finish(struct bpf_object *obj)
{
  if (!obj->efile.elf)
    return;

  elf_end(obj->efile.elf);
  obj->efile.elf = NULL;
  obj->efile.symbols = NULL;
  obj->efile.st_ops_data = NULL;
  obj->efile.st_ops_link_data = NULL;

  zfree(&obj->efile.secs);
  obj->efile.sec_cnt = 0;
  zclose(obj->efile.fd);
  obj->efile.obj_buf = NULL;
  obj->efile.obj_buf_sz = 0;
}

static int bpf_object__elf_init(struct bpf_object *obj)
{
  Elf64_Ehdr *ehdr;
  int err = 0;
  Elf *elf;

  if (obj->efile.elf) {
    pr_warn("elf: init internal error\n");
    return -LIBBPF_ERRNO__LIBELF;
  }

  if (obj->efile.obj_buf_sz > 0) {
    /* obj_buf should have been validated by bpf_object__open_mem(). */
    elf = elf_memory((char *)obj->efile.obj_buf, obj->efile.obj_buf_sz);
  } else {
    obj->efile.fd = open(obj->path, O_RDONLY | O_CLOEXEC);
    if (obj->efile.fd < 0) {
      char errmsg[STRERR_BUFSIZE], *cp;

      err = -errno;
      cp = libbpf_strerror_r(err, errmsg, sizeof(errmsg));
      pr_warn("elf: failed to open %s: %s\n", obj->path, cp);
      return err;
    }

    elf = elf_begin(obj->efile.fd, ELF_C_READ_MMAP, NULL);
  }

  if (!elf) {
    pr_warn("elf: failed to open %s as ELF file: %s\n", obj->path, elf_errmsg(-1));
    err = -LIBBPF_ERRNO__LIBELF;
    goto errout;
  }

  obj->efile.elf = elf;

  if (elf_kind(elf) != ELF_K_ELF) {
    err = -LIBBPF_ERRNO__FORMAT;
    pr_warn("elf: '%s' is not a proper ELF object\n", obj->path);
    goto errout;
  }

  if (gelf_getclass(elf) != ELFCLASS64) {
    err = -LIBBPF_ERRNO__FORMAT;
    pr_warn("elf: '%s' is not a 64-bit ELF object\n", obj->path);
    goto errout;
  }

  obj->efile.ehdr = ehdr = elf64_getehdr(elf);
  if (!obj->efile.ehdr) {
    pr_warn("elf: failed to get ELF header from %s: %s\n", obj->path, elf_errmsg(-1));
    err = -LIBBPF_ERRNO__FORMAT;
    goto errout;
  }

  if (elf_getshdrstrndx(elf, &obj->efile.shstrndx)) {
    pr_warn("elf: failed to get section names section index for %s: %s\n",
      obj->path, elf_errmsg(-1));
    err = -LIBBPF_ERRNO__FORMAT;
    goto errout;
  }

  /* ELF is corrupted/truncated, avoid calling elf_strptr. */
  if (!elf_rawdata(elf_getscn(elf, obj->efile.shstrndx), NULL)) {
    pr_warn("elf: failed to get section names strings from %s: %s\n",
      obj->path, elf_errmsg(-1));
    err = -LIBBPF_ERRNO__FORMAT;
    goto errout;
  }

  /* Old LLVM set e_machine to EM_NONE */
  if (ehdr->e_type != ET_REL || (ehdr->e_machine && ehdr->e_machine != EM_BPF)) {
    pr_warn("elf: %s is not a valid eBPF object file\n", obj->path);
    err = -LIBBPF_ERRNO__FORMAT;
    goto errout;
  }

  return 0;
errout:
  bpf_object__elf_finish(obj);
  return err;
}

static int bpf_object__check_endianness(struct bpf_object *obj)
{
#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
  if (obj->efile.ehdr->e_ident[EI_DATA] == ELFDATA2LSB)
    return 0;
#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
  if (obj->efile.ehdr->e_ident[EI_DATA] == ELFDATA2MSB)
    return 0;
#else
# error "Unrecognized __BYTE_ORDER__"
#endif
  pr_warn("elf: endianness mismatch in %s.\n", obj->path);
  return -LIBBPF_ERRNO__ENDIAN;
}

static int
bpf_object__init_license(struct bpf_object *obj, void *data, size_t size)
{
  if (!data) {
    pr_warn("invalid license section in %s\n", obj->path);
    return -LIBBPF_ERRNO__FORMAT;
  }
  /* libbpf_strlcpy() only copies first N - 1 bytes, so size + 1 won't
   * go over allowed ELF data section buffer
   */
  libbpf_strlcpy(obj->license, data, min(size + 1, sizeof(obj->license)));
  pr_debug("license of %s is %s\n", obj->path, obj->license);
  return 0;
}

static int
bpf_object__init_kversion(struct bpf_object *obj, void *data, size_t size)
{
  __u32 kver;

  if (!data || size != sizeof(kver)) {
    pr_warn("invalid kver section in %s\n", obj->path);
    return -LIBBPF_ERRNO__FORMAT;
  }
  memcpy(&kver, data, sizeof(kver));
  obj->kern_version = kver;
  pr_debug("kernel version of %s is %x\n", obj->path, obj->kern_version);
  return 0;
}

static bool bpf_map_type__is_map_in_map(enum bpf_map_type type)
{
  if (type == BPF_MAP_TYPE_ARRAY_OF_MAPS ||
      type == BPF_MAP_TYPE_HASH_OF_MAPS)
    return true;
  return false;
}

static int find_elf_sec_sz(const struct bpf_object *obj, const char *name, __u32 *size)
{
  Elf_Data *data;
  Elf_Scn *scn;

  if (!name)
    return -EINVAL;

  scn = elf_sec_by_name(obj, name);
  data = elf_sec_data(obj, scn);
  if (data) {
    *size = data->d_size;
    return 0; /* found it */
  }

  return -ENOENT;
}

static Elf64_Sym *find_elf_var_sym(const struct bpf_object *obj, const char *name)
{
  Elf_Data *symbols = obj->efile.symbols;
  const char *sname;
  size_t si;

  for (si = 0; si < symbols->d_size / sizeof(Elf64_Sym); si++) {
    Elf64_Sym *sym = elf_sym_by_idx(obj, si);

    if (ELF64_ST_TYPE(sym->st_info) != STT_OBJECT)
      continue;

    if (ELF64_ST_BIND(sym->st_info) != STB_GLOBAL &&
        ELF64_ST_BIND(sym->st_info) != STB_WEAK)
      continue;

    sname = elf_sym_str(obj, sym->st_name);
    if (!sname) {
      pr_warn("failed to get sym name string for var %s\n", name);
      return ERR_PTR(-EIO);
    }
    if (strcmp(name, sname) == 0)
      return sym;
  }

  return ERR_PTR(-ENOENT);
}

static struct bpf_map *bpf_object__add_map(struct bpf_object *obj)
{
  struct bpf_map *map;
  int err;

  err = libbpf_ensure_mem((void **)&obj->maps, &obj->maps_cap,
        sizeof(*obj->maps), obj->nr_maps + 1);
  if (err)
    return ERR_PTR(err);

  map = &obj->maps[obj->nr_maps++];
  map->obj = obj;
  map->fd = -1;
  map->inner_map_fd = -1;
  map->autocreate = true;

  return map;
}

static size_t bpf_map_mmap_sz(unsigned int value_sz, unsigned int max_entries)
{
  const long page_sz = sysconf(_SC_PAGE_SIZE);
  size_t map_sz;

  map_sz = (size_t)roundup(value_sz, 8) * max_entries;
  map_sz = roundup(map_sz, page_sz);
  return map_sz;
}

static int bpf_map_mmap_resize(struct bpf_map *map, size_t old_sz, size_t new_sz)
{
  void *mmaped;

  if (!map->mmaped)
    return -EINVAL;

  if (old_sz == new_sz)
    return 0;

  mmaped = mmap(NULL, new_sz, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);
  if (mmaped == MAP_FAILED)
    return -errno;

  memcpy(mmaped, map->mmaped, min(old_sz, new_sz));
  munmap(map->mmaped, old_sz);
  map->mmaped = mmaped;
  return 0;
}

static char *internal_map_name(struct bpf_object *obj, const char *real_name)
{
  char map_name[BPF_OBJ_NAME_LEN], *p;
  int pfx_len, sfx_len = max((size_t)7, strlen(real_name));

  /* This is one of the more confusing parts of libbpf for various
   * reasons, some of which are historical. The original idea for naming
   * internal names was to include as much of BPF object name prefix as
   * possible, so that it can be distinguished from similar internal
   * maps of a different BPF object.
   * As an example, let's say we have bpf_object named 'my_object_name'
   * and internal map corresponding to '.rodata' ELF section. The final
   * map name advertised to user and to the kernel will be
   * 'my_objec.rodata', taking first 8 characters of object name and
   * entire 7 characters of '.rodata'.
   * Somewhat confusingly, if internal map ELF section name is shorter
   * than 7 characters, e.g., '.bss', we still reserve 7 characters
   * for the suffix, even though we only have 4 actual characters, and
   * resulting map will be called 'my_objec.bss', not even using all 15
   * characters allowed by the kernel. Oh well, at least the truncated
   * object name is somewhat consistent in this case. But if the map
   * name is '.kconfig', we'll still have entirety of '.kconfig' added
   * (8 chars) and thus will be left with only first 7 characters of the
   * object name ('my_obje'). Happy guessing, user, that the final map
   * name will be "my_obje.kconfig".
   * Now, with libbpf starting to support arbitrarily named .rodata.*
   * and .data.* data sections, it's possible that ELF section name is
   * longer than allowed 15 chars, so we now need to be careful to take
   * only up to 15 first characters of ELF name, taking no BPF object
   * name characters at all. So '.rodata.abracadabra' will result in
   * '.rodata.abracad' kernel and user-visible name.
   * We need to keep this convoluted logic intact for .data, .bss and
   * .rodata maps, but for new custom .data.custom and .rodata.custom
   * maps we use their ELF names as is, not prepending bpf_object name
   * in front. We still need to truncate them to 15 characters for the
   * kernel. Full name can be recovered for such maps by using DATASEC
   * BTF type associated with such map's value type, though.
   */
  if (sfx_len >= BPF_OBJ_NAME_LEN)
    sfx_len = BPF_OBJ_NAME_LEN - 1;

  /* if there are two or more dots in map name, it's a custom dot map */
  if (strchr(real_name + 1, '.') != NULL)
    pfx_len = 0;
  else
    pfx_len = min((size_t)BPF_OBJ_NAME_LEN - sfx_len - 1, strlen(obj->name));

  snprintf(map_name, sizeof(map_name), "%.*s%.*s", pfx_len, obj->name,
     sfx_len, real_name);

  /* sanitise map name to characters allowed by kernel */
  for (p = map_name; *p && p < map_name + sizeof(map_name); p++)
    if (!isalnum(*p) && *p != '_' && *p != '.')
      *p = '_';

  return strdup(map_name);
}

static int
map_fill_btf_type_info(struct bpf_object *obj, struct bpf_map *map);

/* Internal BPF map is mmap()'able only if at least one of corresponding
 * DATASEC's VARs are to be exposed through BPF skeleton. I.e., it's a GLOBAL
 * variable and it's not marked as __hidden (which turns it into, effectively,
 * a STATIC variable).
 */
static bool map_is_mmapable(struct bpf_object *obj, struct bpf_map *map)
{
  const struct btf_type *t, *vt;
  struct btf_var_secinfo *vsi;
  int i, n;

  if (!map->btf_value_type_id)
    return false;

  t = btf__type_by_id(obj->btf, map->btf_value_type_id);
  if (!btf_is_datasec(t))
    return false;

  vsi = btf_var_secinfos(t);
  for (i = 0, n = btf_vlen(t); i < n; i++, vsi++) {
    vt = btf__type_by_id(obj->btf, vsi->type);
    if (!btf_is_var(vt))
      continue;

    if (btf_var(vt)->linkage != BTF_VAR_STATIC)
      return true;
  }

  return false;
}

static int
bpf_object__init_internal_map(struct bpf_object *obj, enum libbpf_map_type type,
            const char *real_name, int sec_idx, void *data, size_t data_sz)
{
  struct bpf_map_def *def;
  struct bpf_map *map;
  size_t mmap_sz;
  int err;

  map = bpf_object__add_map(obj);
  if (IS_ERR(map))
    return PTR_ERR(map);

  map->libbpf_type = type;
  map->sec_idx = sec_idx;
  map->sec_offset = 0;
  map->real_name = strdup(real_name);
  map->name = internal_map_name(obj, real_name);
  if (!map->real_name || !map->name) {
    zfree(&map->real_name);
    zfree(&map->name);
    return -ENOMEM;
  }

  def = &map->def;
  def->type = BPF_MAP_TYPE_ARRAY;
  def->key_size = sizeof(int);
  def->value_size = data_sz;
  def->max_entries = 1;
  def->map_flags = type == LIBBPF_MAP_RODATA || type == LIBBPF_MAP_KCONFIG
       ? BPF_F_RDONLY_PROG : 0;

  /* failures are fine because of maps like .rodata.str1.1 */
  (void) map_fill_btf_type_info(obj, map);

  if (map_is_mmapable(obj, map))
    def->map_flags |= BPF_F_MMAPABLE;

  pr_debug("map '%s' (global data): at sec_idx %d, offset %zu, flags %x.\n",
     map->name, map->sec_idx, map->sec_offset, def->map_flags);

  mmap_sz = bpf_map_mmap_sz(map->def.value_size, map->def.max_entries);
  map->mmaped = mmap(NULL, mmap_sz, PROT_READ | PROT_WRITE,
         MAP_SHARED | MAP_ANONYMOUS, -1, 0);
  if (map->mmaped == MAP_FAILED) {
    err = -errno;
    map->mmaped = NULL;
    pr_warn("failed to alloc map '%s' content buffer: %d\n",
      map->name, err);
    zfree(&map->real_name);
    zfree(&map->name);
    return err;
  }

  if (data)
    memcpy(map->mmaped, data, data_sz);

  pr_debug("map %td is \"%s\"\n", map - obj->maps, map->name);
  return 0;
}

static int bpf_object__init_global_data_maps(struct bpf_object *obj)
{
  struct elf_sec_desc *sec_desc;
  const char *sec_name;
  int err = 0, sec_idx;

  /*
   * Populate obj->maps with libbpf internal maps.
   */
  for (sec_idx = 1; sec_idx < obj->efile.sec_cnt; sec_idx++) {
    sec_desc = &obj->efile.secs[sec_idx];

    /* Skip recognized sections with size 0. */
    if (!sec_desc->data || sec_desc->data->d_size == 0)
      continue;

    switch (sec_desc->sec_type) {
    case SEC_DATA:
      sec_name = elf_sec_name(obj, elf_sec_by_idx(obj, sec_idx));
      err = bpf_object__init_internal_map(obj, LIBBPF_MAP_DATA,
                  sec_name, sec_idx,
                  sec_desc->data->d_buf,
                  sec_desc->data->d_size);
      break;
    case SEC_RODATA:
      obj->has_rodata = true;
      sec_name = elf_sec_name(obj, elf_sec_by_idx(obj, sec_idx));
      err = bpf_object__init_internal_map(obj, LIBBPF_MAP_RODATA,
                  sec_name, sec_idx,
                  sec_desc->data->d_buf,
                  sec_desc->data->d_size);
      break;
    case SEC_BSS:
      sec_name = elf_sec_name(obj, elf_sec_by_idx(obj, sec_idx));
      err = bpf_object__init_internal_map(obj, LIBBPF_MAP_BSS,
                  sec_name, sec_idx,
                  NULL,
                  sec_desc->data->d_size);
      break;
    default:
      /* skip */
      break;
    }
    if (err)
      return err;
  }
  return 0;
}


static struct extern_desc *find_extern_by_name(const struct bpf_object *obj,
                 const void *name)
{
  int i;

  for (i = 0; i < obj->nr_extern; i++) {
    if (strcmp(obj->externs[i].name, name) == 0)
      return &obj->externs[i];
  }
  return NULL;
}

static int set_kcfg_value_tri(struct extern_desc *ext, void *ext_val,
            char value)
{
  switch (ext->kcfg.type) {
  case KCFG_BOOL:
    if (value == 'm') {
      pr_warn("extern (kcfg) '%s': value '%c' implies tristate or char type\n",
        ext->name, value);
      return -EINVAL;
    }
    *(bool *)ext_val = value == 'y' ? true : false;
    break;
  case KCFG_TRISTATE:
    if (value == 'y')
      *(enum libbpf_tristate *)ext_val = TRI_YES;
    else if (value == 'm')
      *(enum libbpf_tristate *)ext_val = TRI_MODULE;
    else /* value == 'n' */
      *(enum libbpf_tristate *)ext_val = TRI_NO;
    break;
  case KCFG_CHAR:
    *(char *)ext_val = value;
    break;
  case KCFG_UNKNOWN:
  case KCFG_INT:
  case KCFG_CHAR_ARR:
  default:
    pr_warn("extern (kcfg) '%s': value '%c' implies bool, tristate, or char type\n",
      ext->name, value);
    return -EINVAL;
  }
  ext->is_set = true;
  return 0;
}

static int set_kcfg_value_str(struct extern_desc *ext, char *ext_val,
            const char *value)
{
  size_t len;

  if (ext->kcfg.type != KCFG_CHAR_ARR) {
    pr_warn("extern (kcfg) '%s': value '%s' implies char array type\n",
      ext->name, value);
    return -EINVAL;
  }

  len = strlen(value);
  if (value[len - 1] != '"') {
    pr_warn("extern (kcfg) '%s': invalid string config '%s'\n",
      ext->name, value);
    return -EINVAL;
  }

  /* strip quotes */
  len -= 2;
  if (len >= ext->kcfg.sz) {
    pr_warn("extern (kcfg) '%s': long string '%s' of (%zu bytes) truncated to %d bytes\n",
      ext->name, value, len, ext->kcfg.sz - 1);
    len = ext->kcfg.sz - 1;
  }
  memcpy(ext_val, value + 1, len);
  ext_val[len] = '\0';
  ext->is_set = true;
  return 0;
}

static int parse_u64(const char *value, __u64 *res)
{
  char *value_end;
  int err;

  errno = 0;
  *res = strtoull(value, &value_end, 0);
  if (errno) {
    err = -errno;
    pr_warn("failed to parse '%s' as integer: %d\n", value, err);
    return err;
  }
  if (*value_end) {
    pr_warn("failed to parse '%s' as integer completely\n", value);
    return -EINVAL;
  }
  return 0;
}

static bool is_kcfg_value_in_range(const struct extern_desc *ext, __u64 v)
{
  int bit_sz = ext->kcfg.sz * 8;

  if (ext->kcfg.sz == 8)
    return true;

  /* Validate that value stored in u64 fits in integer of `ext->sz`
   * bytes size without any loss of information. If the target integer
   * is signed, we rely on the following limits of integer type of
   * Y bits and subsequent transformation:
   *
   *     -2^(Y-1) <= X           <= 2^(Y-1) - 1
   *            0 <= X + 2^(Y-1) <= 2^Y - 1
   *            0 <= X + 2^(Y-1) <  2^Y
   *
   *  For unsigned target integer, check that all the (64 - Y) bits are
   *  zero.
   */
  if (ext->kcfg.is_signed)
    return v + (1ULL << (bit_sz - 1)) < (1ULL << bit_sz);
  else
    return (v >> bit_sz) == 0;
}

static int set_kcfg_value_num(struct extern_desc *ext, void *ext_val,
            __u64 value)
{
  if (ext->kcfg.type != KCFG_INT && ext->kcfg.type != KCFG_CHAR &&
      ext->kcfg.type != KCFG_BOOL) {
    pr_warn("extern (kcfg) '%s': value '%llu' implies integer, char, or boolean type\n",
      ext->name, (unsigned long long)value);
    return -EINVAL;
  }
  if (ext->kcfg.type == KCFG_BOOL && value > 1) {
    pr_warn("extern (kcfg) '%s': value '%llu' isn't boolean compatible\n",
      ext->name, (unsigned long long)value);
    return -EINVAL;

  }
  if (!is_kcfg_value_in_range(ext, value)) {
    pr_warn("extern (kcfg) '%s': value '%llu' doesn't fit in %d bytes\n",
      ext->name, (unsigned long long)value, ext->kcfg.sz);
    return -ERANGE;
  }
  switch (ext->kcfg.sz) {
  case 1:
    *(__u8 *)ext_val = value;
    break;
  case 2:
    *(__u16 *)ext_val = value;
    break;
  case 4:
    *(__u32 *)ext_val = value;
    break;
  case 8:
    *(__u64 *)ext_val = value;
    break;
  default:
    return -EINVAL;
  }
  ext->is_set = true;
  return 0;
}

static int bpf_object__process_kconfig_line(struct bpf_object *obj,
              char *buf, void *data)
{
  struct extern_desc *ext;
  char *sep, *value;
  int len, err = 0;
  void *ext_val;
  __u64 num;

  if (!str_has_pfx(buf, "CONFIG_"))
    return 0;

  sep = strchr(buf, '=');
  if (!sep) {
    pr_warn("failed to parse '%s': no separator\n", buf);
    return -EINVAL;
  }

  /* Trim ending '\n' */
  len = strlen(buf);
  if (buf[len - 1] == '\n')
    buf[len - 1] = '\0';
  /* Split on '=' and ensure that a value is present. */
  *sep = '\0';
  if (!sep[1]) {
    *sep = '=';
    pr_warn("failed to parse '%s': no value\n", buf);
    return -EINVAL;
  }

  ext = find_extern_by_name(obj, buf);
  if (!ext || ext->is_set)
    return 0;

  ext_val = data + ext->kcfg.data_off;
  value = sep + 1;

  switch (*value) {
  case 'y': case 'n': case 'm':
    err = set_kcfg_value_tri(ext, ext_val, *value);
    break;
  case '"':
    err = set_kcfg_value_str(ext, ext_val, value);
    break;
  default:
    /* assume integer */
    err = parse_u64(value, &num);
    if (err) {
      pr_warn("extern (kcfg) '%s': value '%s' isn't a valid integer\n", ext->name, value);
      return err;
    }
    if (ext->kcfg.type != KCFG_INT && ext->kcfg.type != KCFG_CHAR) {
      pr_warn("extern (kcfg) '%s': value '%s' implies integer type\n", ext->name, value);
      return -EINVAL;
    }
    err = set_kcfg_value_num(ext, ext_val, num);
    break;
  }
  if (err)
    return err;
  pr_debug("extern (kcfg) '%s': set to %s\n", ext->name, value);
  return 0;
}

static int bpf_object__read_kconfig_file(struct bpf_object *obj, void *data)
{
  char buf[PATH_MAX];
  struct utsname uts;
  int len, err = 0;
  gzFile file;

  uname(&uts);
  len = snprintf(buf, PATH_MAX, "/boot/config-%s", uts.release);
  if (len < 0)
    return -EINVAL;
  else if (len >= PATH_MAX)
    return -ENAMETOOLONG;

  /* gzopen also accepts uncompressed files. */
  file = gzopen(buf, "re");
  if (!file)
    file = gzopen("/proc/config.gz", "re");

  if (!file) {
    pr_warn("failed to open system Kconfig\n");
    return -ENOENT;
  }

  while (gzgets(file, buf, sizeof(buf))) {
    err = bpf_object__process_kconfig_line(obj, buf, data);
    if (err) {
      pr_warn("error parsing system Kconfig line '%s': %d\n",
        buf, err);
      goto out;
    }
  }

out:
  gzclose(file);
  return err;
}

static int bpf_object__read_kconfig_mem(struct bpf_object *obj,
          const char *config, void *data)
{
  char buf[PATH_MAX];
  int err = 0;
  FILE *file;

  file = fmemopen((void *)config, strlen(config), "r");
  if (!file) {
    err = -errno;
    pr_warn("failed to open in-memory Kconfig: %d\n", err);
    return err;
  }

  while (fgets(buf, sizeof(buf), file)) {
    err = bpf_object__process_kconfig_line(obj, buf, data);
    if (err) {
      pr_warn("error parsing in-memory Kconfig line '%s': %d\n",
        buf, err);
      break;
    }
  }

  fclose(file);
  return err;
}

static int bpf_object__init_kconfig_map(struct bpf_object *obj)
{
  struct extern_desc *last_ext = NULL, *ext;
  size_t map_sz;
  int i, err;

  for (i = 0; i < obj->nr_extern; i++) {
    ext = &obj->externs[i];
    if (ext->type == EXT_KCFG)
      last_ext = ext;
  }

  if (!last_ext)
    return 0;

  map_sz = last_ext->kcfg.data_off + last_ext->kcfg.sz;
  err = bpf_object__init_internal_map(obj, LIBBPF_MAP_KCONFIG,
              ".kconfig", obj->efile.symbols_shndx,
              NULL, map_sz);
  if (err)
    return err;

  obj->kconfig_map_idx = obj->nr_maps - 1;

  return 0;
}

const struct btf_type *
skip_mods_and_typedefs(const struct btf *btf, __u32 id, __u32 *res_id)
{
  const struct btf_type *t = btf__type_by_id(btf, id);

  if (res_id)
    *res_id = id;

  while (btf_is_mod(t) || btf_is_typedef(t)) {
    if (res_id)
      *res_id = t->type;
    t = btf__type_by_id(btf, t->type);
  }

  return t;
}

static const struct btf_type *
resolve_func_ptr(const struct btf *btf, __u32 id, __u32 *res_id)
{
  const struct btf_type *t;

  t = skip_mods_and_typedefs(btf, id, NULL);
  if (!btf_is_ptr(t))
    return NULL;

  t = skip_mods_and_typedefs(btf, t->type, res_id);

  return btf_is_func_proto(t) ? t : NULL;
}

static const char *__btf_kind_str(__u16 kind)
{
  switch (kind) {
  case BTF_KIND_UNKN: return "void";
  case BTF_KIND_INT: return "int";
  case BTF_KIND_PTR: return "ptr";
  case BTF_KIND_ARRAY: return "array";
  case BTF_KIND_STRUCT: return "struct";
  case BTF_KIND_UNION: return "union";
  case BTF_KIND_ENUM: return "enum";
  case BTF_KIND_FWD: return "fwd";
  case BTF_KIND_TYPEDEF: return "typedef";
  case BTF_KIND_VOLATILE: return "volatile";
  case BTF_KIND_CONST: return "const";
  case BTF_KIND_RESTRICT: return "restrict";
  case BTF_KIND_FUNC: return "func";
  case BTF_KIND_FUNC_PROTO: return "func_proto";
  case BTF_KIND_VAR: return "var";
  case BTF_KIND_DATASEC: return "datasec";
  case BTF_KIND_FLOAT: return "float";
  case BTF_KIND_DECL_TAG: return "decl_tag";
  case BTF_KIND_TYPE_TAG: return "type_tag";
  case BTF_KIND_ENUM64: return "enum64";
  default: return "unknown";
  }
}

const char *btf_kind_str(const struct btf_type *t)
{
  return __btf_kind_str(btf_kind(t));
}

/*
 * Fetch integer attribute of BTF map definition. Such attributes are
 * represented using a pointer to an array, in which dimensionality of array
 * encodes specified integer value. E.g., int (*type)[BPF_MAP_TYPE_ARRAY];
 * encodes `type => BPF_MAP_TYPE_ARRAY` key/value pair completely using BTF
 * type definition, while using only sizeof(void *) space in ELF data section.
 */
static bool get_map_field_int(const char *map_name, const struct btf *btf,
            const struct btf_member *m, __u32 *res)
{
  const struct btf_type *t = skip_mods_and_typedefs(btf, m->type, NULL);
  const char *name = btf__name_by_offset(btf, m->name_off);
  const struct btf_array *arr_info;
  const struct btf_type *arr_t;

  if (!btf_is_ptr(t)) {
    pr_warn("map '%s': attr '%s': expected PTR, got %s.\n",
      map_name, name, btf_kind_str(t));
    return false;
  }

  arr_t = btf__type_by_id(btf, t->type);
  if (!arr_t) {
    pr_warn("map '%s': attr '%s': type [%u] not found.\n",
      map_name, name, t->type);
    return false;
  }
  if (!btf_is_array(arr_t)) {
    pr_warn("map '%s': attr '%s': expected ARRAY, got %s.\n",
      map_name, name, btf_kind_str(arr_t));
    return false;
  }
  arr_info = btf_array(arr_t);
  *res = arr_info->nelems;
  return true;
}

static int pathname_concat(char *buf, size_t buf_sz, const char *path, const char *name)
{
  int len;

  len = snprintf(buf, buf_sz, "%s/%s", path, name);
  if (len < 0)
    return -EINVAL;
  if (len >= buf_sz)
    return -ENAMETOOLONG;

  return 0;
}

static int build_map_pin_path(struct bpf_map *map, const char *path)
{
  char buf[PATH_MAX];
  int err;

  if (!path)
    path = "/sys/fs/bpf";

  err = pathname_concat(buf, sizeof(buf), path, bpf_map__name(map));
  if (err)
    return err;

  return bpf_map__set_pin_path(map, buf);
}

/* should match definition in bpf_helpers.h */
enum libbpf_pin_type {
  LIBBPF_PIN_NONE,
  /* PIN_BY_NAME: pin maps by name (in /sys/fs/bpf by default) */
  LIBBPF_PIN_BY_NAME,
};

int parse_btf_map_def(const char *map_name, struct btf *btf,
          const struct btf_type *def_t, bool strict,
          struct btf_map_def *map_def, struct btf_map_def *inner_def)
{
  const struct btf_type *t;
  const struct btf_member *m;
  bool is_inner = inner_def == NULL;
  int vlen, i;

  vlen = btf_vlen(def_t);
  m = btf_members(def_t);
  for (i = 0; i < vlen; i++, m++) {
    const char *name = btf__name_by_offset(btf, m->name_off);

    if (!name) {
      pr_warn("map '%s': invalid field #%d.\n", map_name, i);
      return -EINVAL;
    }
    if (strcmp(name, "type") == 0) {
      if (!get_map_field_int(map_name, btf, m, &map_def->map_type))
        return -EINVAL;
      map_def->parts |= MAP_DEF_MAP_TYPE;
    } else if (strcmp(name, "max_entries") == 0) {
      if (!get_map_field_int(map_name, btf, m, &map_def->max_entries))
        return -EINVAL;
      map_def->parts |= MAP_DEF_MAX_ENTRIES;
    } else if (strcmp(name, "map_flags") == 0) {
      if (!get_map_field_int(map_name, btf, m, &map_def->map_flags))
        return -EINVAL;
      map_def->parts |= MAP_DEF_MAP_FLAGS;
    } else if (strcmp(name, "numa_node") == 0) {
      if (!get_map_field_int(map_name, btf, m, &map_def->numa_node))
        return -EINVAL;
      map_def->parts |= MAP_DEF_NUMA_NODE;
    } else if (strcmp(name, "key_size") == 0) {
      __u32 sz;

      if (!get_map_field_int(map_name, btf, m, &sz))
        return -EINVAL;
      if (map_def->key_size && map_def->key_size != sz) {
        pr_warn("map '%s': conflicting key size %u != %u.\n",
          map_name, map_def->key_size, sz);
        return -EINVAL;
      }
      map_def->key_size = sz;
      map_def->parts |= MAP_DEF_KEY_SIZE;
    } else if (strcmp(name, "key") == 0) {
      __s64 sz;

      t = btf__type_by_id(btf, m->type);
      if (!t) {
        pr_warn("map '%s': key type [%d] not found.\n",
          map_name, m->type);
        return -EINVAL;
      }
      if (!btf_is_ptr(t)) {
        pr_warn("map '%s': key spec is not PTR: %s.\n",
          map_name, btf_kind_str(t));
        return -EINVAL;
      }
      sz = btf__resolve_size(btf, t->type);
      if (sz < 0) {
        pr_warn("map '%s': can't determine key size for type [%u]: %zd.\n",
          map_name, t->type, (ssize_t)sz);
        return sz;
      }
      if (map_def->key_size && map_def->key_size != sz) {
        pr_warn("map '%s': conflicting key size %u != %zd.\n",
          map_name, map_def->key_size, (ssize_t)sz);
        return -EINVAL;
      }
      map_def->key_size = sz;
      map_def->key_type_id = t->type;
      map_def->parts |= MAP_DEF_KEY_SIZE | MAP_DEF_KEY_TYPE;
    } else if (strcmp(name, "value_size") == 0) {
      __u32 sz;

      if (!get_map_field_int(map_name, btf, m, &sz))
        return -EINVAL;
      if (map_def->value_size && map_def->value_size != sz) {
        pr_warn("map '%s': conflicting value size %u != %u.\n",
          map_name, map_def->value_size, sz);
        return -EINVAL;
      }
      map_def->value_size = sz;
      map_def->parts |= MAP_DEF_VALUE_SIZE;
    } else if (strcmp(name, "value") == 0) {
      __s64 sz;

      t = btf__type_by_id(btf, m->type);
      if (!t) {
        pr_warn("map '%s': value type [%d] not found.\n",
          map_name, m->type);
        return -EINVAL;
      }
      if (!btf_is_ptr(t)) {
        pr_warn("map '%s': value spec is not PTR: %s.\n",
          map_name, btf_kind_str(t));
        return -EINVAL;
      }
      sz = btf__resolve_size(btf, t->type);
      if (sz < 0) {
        pr_warn("map '%s': can't determine value size for type [%u]: %zd.\n",
          map_name, t->type, (ssize_t)sz);
        return sz;
      }
      if (map_def->value_size && map_def->value_size != sz) {
        pr_warn("map '%s': conflicting value size %u != %zd.\n",
          map_name, map_def->value_size, (ssize_t)sz);
        return -EINVAL;
      }
      map_def->value_size = sz;
      map_def->value_type_id = t->type;
      map_def->parts |= MAP_DEF_VALUE_SIZE | MAP_DEF_VALUE_TYPE;
    }
    else if (strcmp(name, "values") == 0) {
      bool is_map_in_map = bpf_map_type__is_map_in_map(map_def->map_type);
      bool is_prog_array = map_def->map_type == BPF_MAP_TYPE_PROG_ARRAY;
      const char *desc = is_map_in_map ? "map-in-map inner" : "prog-array value";
      char inner_map_name[128];
      int err;

      if (is_inner) {
        pr_warn("map '%s': multi-level inner maps not supported.\n",
          map_name);
        return -ENOTSUP;
      }
      if (i != vlen - 1) {
        pr_warn("map '%s': '%s' member should be last.\n",
          map_name, name);
        return -EINVAL;
      }
      if (!is_map_in_map && !is_prog_array) {
        pr_warn("map '%s': should be map-in-map or prog-array.\n",
          map_name);
        return -ENOTSUP;
      }
      if (map_def->value_size && map_def->value_size != 4) {
        pr_warn("map '%s': conflicting value size %u != 4.\n",
          map_name, map_def->value_size);
        return -EINVAL;
      }
      map_def->value_size = 4;
      t = btf__type_by_id(btf, m->type);
      if (!t) {
        pr_warn("map '%s': %s type [%d] not found.\n",
          map_name, desc, m->type);
        return -EINVAL;
      }
      if (!btf_is_array(t) || btf_array(t)->nelems) {
        pr_warn("map '%s': %s spec is not a zero-sized array.\n",
          map_name, desc);
        return -EINVAL;
      }
      t = skip_mods_and_typedefs(btf, btf_array(t)->type, NULL);
      if (!btf_is_ptr(t)) {
        pr_warn("map '%s': %s def is of unexpected kind %s.\n",
          map_name, desc, btf_kind_str(t));
        return -EINVAL;
      }
      t = skip_mods_and_typedefs(btf, t->type, NULL);
      if (is_prog_array) {
        if (!btf_is_func_proto(t)) {
          pr_warn("map '%s': prog-array value def is of unexpected kind %s.\n",
            map_name, btf_kind_str(t));
          return -EINVAL;
        }
        continue;
      }
      if (!btf_is_struct(t)) {
        pr_warn("map '%s': map-in-map inner def is of unexpected kind %s.\n",
          map_name, btf_kind_str(t));
        return -EINVAL;
      }

      snprintf(inner_map_name, sizeof(inner_map_name), "%s.inner", map_name);
      err = parse_btf_map_def(inner_map_name, btf, t, strict, inner_def, NULL);
      if (err)
        return err;

      map_def->parts |= MAP_DEF_INNER_MAP;
    } else if (strcmp(name, "pinning") == 0) {
      __u32 val;

      if (is_inner) {
        pr_warn("map '%s': inner def can't be pinned.\n", map_name);
        return -EINVAL;
      }
      if (!get_map_field_int(map_name, btf, m, &val))
        return -EINVAL;
      if (val != LIBBPF_PIN_NONE && val != LIBBPF_PIN_BY_NAME) {
        pr_warn("map '%s': invalid pinning value %u.\n",
          map_name, val);
        return -EINVAL;
      }
      map_def->pinning = val;
      map_def->parts |= MAP_DEF_PINNING;
    } else if (strcmp(name, "map_extra") == 0) {
      __u32 map_extra;

      if (!get_map_field_int(map_name, btf, m, &map_extra))
        return -EINVAL;
      map_def->map_extra = map_extra;
      map_def->parts |= MAP_DEF_MAP_EXTRA;
    } else {
      if (strict) {
        pr_warn("map '%s': unknown field '%s'.\n", map_name, name);
        return -ENOTSUP;
      }
      pr_debug("map '%s': ignoring unknown field '%s'.\n", map_name, name);
    }
  }

  if (map_def->map_type == BPF_MAP_TYPE_UNSPEC) {
    pr_warn("map '%s': map type isn't specified.\n", map_name);
    return -EINVAL;
  }

  return 0;
}

static size_t adjust_ringbuf_sz(size_t sz)
{
  __u32 page_sz = sysconf(_SC_PAGE_SIZE);
  __u32 mul;

  /* if user forgot to set any size, make sure they see error */
  if (sz == 0)
    return 0;
  /* Kernel expects BPF_MAP_TYPE_RINGBUF's max_entries to be
   * a power-of-2 multiple of kernel's page size. If user diligently
   * satisified these conditions, pass the size through.
   */
  if ((sz % page_sz) == 0 && is_pow_of_2(sz / page_sz))
    return sz;

  /* Otherwise find closest (page_sz * power_of_2) product bigger than
   * user-set size to satisfy both user size request and kernel
   * requirements and substitute correct max_entries for map creation.
   */
  for (mul = 1; mul <= UINT_MAX / page_sz; mul <<= 1) {
    if (mul * page_sz > sz)
      return mul * page_sz;
  }

  /* if it's impossible to satisfy the conditions (i.e., user size is
   * very close to UINT_MAX but is not a power-of-2 multiple of
   * page_size) then just return original size and let kernel reject it
   */
  return sz;
}

static bool map_is_ringbuf(const struct bpf_map *map)
{
  return map->def.type == BPF_MAP_TYPE_RINGBUF ||
         map->def.type == BPF_MAP_TYPE_USER_RINGBUF;
}

static void fill_map_from_def(struct bpf_map *map, const struct btf_map_def *def)
{
  map->def.type = def->map_type;
  map->def.key_size = def->key_size;
  map->def.value_size = def->value_size;
  map->def.max_entries = def->max_entries;
  map->def.map_flags = def->map_flags;
  map->map_extra = def->map_extra;

  map->numa_node = def->numa_node;
  map->btf_key_type_id = def->key_type_id;
  map->btf_value_type_id = def->value_type_id;

  /* auto-adjust BPF ringbuf map max_entries to be a multiple of page size */
  if (map_is_ringbuf(map))
    map->def.max_entries = adjust_ringbuf_sz(map->def.max_entries);

  if (def->parts & MAP_DEF_MAP_TYPE)
    pr_debug("map '%s': found type = %u.\n", map->name, def->map_type);

  if (def->parts & MAP_DEF_KEY_TYPE)
    pr_debug("map '%s': found key [%u], sz = %u.\n",
       map->name, def->key_type_id, def->key_size);
  else if (def->parts & MAP_DEF_KEY_SIZE)
    pr_debug("map '%s': found key_size = %u.\n", map->name, def->key_size);

  if (def->parts & MAP_DEF_VALUE_TYPE)
    pr_debug("map '%s': found value [%u], sz = %u.\n",
       map->name, def->value_type_id, def->value_size);
  else if (def->parts & MAP_DEF_VALUE_SIZE)
    pr_debug("map '%s': found value_size = %u.\n", map->name, def->value_size);

  if (def->parts & MAP_DEF_MAX_ENTRIES)
    pr_debug("map '%s': found max_entries = %u.\n", map->name, def->max_entries);
  if (def->parts & MAP_DEF_MAP_FLAGS)
    pr_debug("map '%s': found map_flags = 0x%x.\n", map->name, def->map_flags);
  if (def->parts & MAP_DEF_MAP_EXTRA)
    pr_debug("map '%s': found map_extra = 0x%llx.\n", map->name,
       (unsigned long long)def->map_extra);
  if (def->parts & MAP_DEF_PINNING)
    pr_debug("map '%s': found pinning = %u.\n", map->name, def->pinning);
  if (def->parts & MAP_DEF_NUMA_NODE)
    pr_debug("map '%s': found numa_node = %u.\n", map->name, def->numa_node);

  if (def->parts & MAP_DEF_INNER_MAP)
    pr_debug("map '%s': found inner map definition.\n", map->name);
}

static const char *btf_var_linkage_str(__u32 linkage)
{
  switch (linkage) {
  case BTF_VAR_STATIC: return "static";
  case BTF_VAR_GLOBAL_ALLOCATED: return "global";
  case BTF_VAR_GLOBAL_EXTERN: return "extern";
  default: return "unknown";
  }
}

static int bpf_object__init_user_btf_map(struct bpf_object *obj,
           const struct btf_type *sec,
           int var_idx, int sec_idx,
           const Elf_Data *data, bool strict,
           const char *pin_root_path)
{
  struct btf_map_def map_def = {}, inner_def = {};
  const struct btf_type *var, *def;
  const struct btf_var_secinfo *vi;
  const struct btf_var *var_extra;
  const char *map_name;
  struct bpf_map *map;
  int err;

  vi = btf_var_secinfos(sec) + var_idx;
  var = btf__type_by_id(obj->btf, vi->type);
  var_extra = btf_var(var);
  map_name = btf__name_by_offset(obj->btf, var->name_off);

  if (map_name == NULL || map_name[0] == '\0') {
    pr_warn("map #%d: empty name.\n", var_idx);
    return -EINVAL;
  }
  if ((__u64)vi->offset + vi->size > data->d_size) {
    pr_warn("map '%s' BTF data is corrupted.\n", map_name);
    return -EINVAL;
  }
  if (!btf_is_var(var)) {
    pr_warn("map '%s': unexpected var kind %s.\n",
      map_name, btf_kind_str(var));
    return -EINVAL;
  }
  if (var_extra->linkage != BTF_VAR_GLOBAL_ALLOCATED) {
    pr_warn("map '%s': unsupported map linkage %s.\n",
      map_name, btf_var_linkage_str(var_extra->linkage));
    return -EOPNOTSUPP;
  }

  def = skip_mods_and_typedefs(obj->btf, var->type, NULL);
  if (!btf_is_struct(def)) {
    pr_warn("map '%s': unexpected def kind %s.\n",
      map_name, btf_kind_str(var));
    return -EINVAL;
  }
  if (def->size > vi->size) {
    pr_warn("map '%s': invalid def size.\n", map_name);
    return -EINVAL;
  }

  map = bpf_object__add_map(obj);
  if (IS_ERR(map))
    return PTR_ERR(map);
  map->name = strdup(map_name);
  if (!map->name) {
    pr_warn("map '%s': failed to alloc map name.\n", map_name);
    return -ENOMEM;
  }
  map->libbpf_type = LIBBPF_MAP_UNSPEC;
  map->def.type = BPF_MAP_TYPE_UNSPEC;
  map->sec_idx = sec_idx;
  map->sec_offset = vi->offset;
  map->btf_var_idx = var_idx;
  pr_debug("map '%s': at sec_idx %d, offset %zu.\n",
     map_name, map->sec_idx, map->sec_offset);

  err = parse_btf_map_def(map->name, obj->btf, def, strict, &map_def, &inner_def);
  if (err)
    return err;

  fill_map_from_def(map, &map_def);

  if (map_def.pinning == LIBBPF_PIN_BY_NAME) {
    err = build_map_pin_path(map, pin_root_path);
    if (err) {
      pr_warn("map '%s': couldn't build pin path.\n", map->name);
      return err;
    }
  }

  if (map_def.parts & MAP_DEF_INNER_MAP) {
    map->inner_map = calloc(1, sizeof(*map->inner_map));
    if (!map->inner_map)
      return -ENOMEM;
    map->inner_map->fd = -1;
    map->inner_map->sec_idx = sec_idx;
    map->inner_map->name = malloc(strlen(map_name) + sizeof(".inner") + 1);
    if (!map->inner_map->name)
      return -ENOMEM;
    sprintf(map->inner_map->name, "%s.inner", map_name);

    fill_map_from_def(map->inner_map, &inner_def);
  }

  err = map_fill_btf_type_info(obj, map);
  if (err)
    return err;

  return 0;
}

static int bpf_object__init_user_btf_maps(struct bpf_object *obj, bool strict,
            const char *pin_root_path)
{
  const struct btf_type *sec = NULL;
  int nr_types, i, vlen, err;
  const struct btf_type *t;
  const char *name;
  Elf_Data *data;
  Elf_Scn *scn;

  if (obj->efile.btf_maps_shndx < 0)
    return 0;

  scn = elf_sec_by_idx(obj, obj->efile.btf_maps_shndx);
  data = elf_sec_data(obj, scn);
  if (!scn || !data) {
    pr_warn("elf: failed to get %s map definitions for %s\n",
      MAPS_ELF_SEC, obj->path);
    return -EINVAL;
  }

  nr_types = btf__type_cnt(obj->btf);
  for (i = 1; i < nr_types; i++) {
    t = btf__type_by_id(obj->btf, i);
    if (!btf_is_datasec(t))
      continue;
    name = btf__name_by_offset(obj->btf, t->name_off);
    if (strcmp(name, MAPS_ELF_SEC) == 0) {
      sec = t;
      obj->efile.btf_maps_sec_btf_id = i;
      break;
    }
  }

  if (!sec) {
    pr_warn("DATASEC '%s' not found.\n", MAPS_ELF_SEC);
    return -ENOENT;
  }

  vlen = btf_vlen(sec);
  for (i = 0; i < vlen; i++) {
    err = bpf_object__init_user_btf_map(obj, sec, i,
                obj->efile.btf_maps_shndx,
                data, strict,
                pin_root_path);
    if (err)
      return err;
  }

  return 0;
}

static int bpf_object__init_maps(struct bpf_object *obj,
         const struct bpf_object_open_opts *opts)
{
  const char *pin_root_path;
  bool strict;
  int err = 0;

  strict = !OPTS_GET(opts, relaxed_maps, false);
  pin_root_path = OPTS_GET(opts, pin_root_path, NULL);

  err = bpf_object__init_user_btf_maps(obj, strict, pin_root_path);
  err = err ?: bpf_object__init_global_data_maps(obj);
  err = err ?: bpf_object__init_kconfig_map(obj);
  err = err ?: bpf_object_init_struct_ops(obj);

  return err;
}

static bool section_have_execinstr(struct bpf_object *obj, int idx)
{
  Elf64_Shdr *sh;

  sh = elf_sec_hdr(obj, elf_sec_by_idx(obj, idx));
  if (!sh)
    return false;

  return sh->sh_flags & SHF_EXECINSTR;
}

static bool btf_needs_sanitization(struct bpf_object *obj)
{
  bool has_func_global = kernel_supports(obj, FEAT_BTF_GLOBAL_FUNC);
  bool has_datasec = kernel_supports(obj, FEAT_BTF_DATASEC);
  bool has_float = kernel_supports(obj, FEAT_BTF_FLOAT);
  bool has_func = kernel_supports(obj, FEAT_BTF_FUNC);
  bool has_decl_tag = kernel_supports(obj, FEAT_BTF_DECL_TAG);
  bool has_type_tag = kernel_supports(obj, FEAT_BTF_TYPE_TAG);
  bool has_enum64 = kernel_supports(obj, FEAT_BTF_ENUM64);

  return !has_func || !has_datasec || !has_func_global || !has_float ||
         !has_decl_tag || !has_type_tag || !has_enum64;
}

static int bpf_object__sanitize_btf(struct bpf_object *obj, struct btf *btf)
{
  bool has_func_global = kernel_supports(obj, FEAT_BTF_GLOBAL_FUNC);
  bool has_datasec = kernel_supports(obj, FEAT_BTF_DATASEC);
  bool has_float = kernel_supports(obj, FEAT_BTF_FLOAT);
  bool has_func = kernel_supports(obj, FEAT_BTF_FUNC);
  bool has_decl_tag = kernel_supports(obj, FEAT_BTF_DECL_TAG);
  bool has_type_tag = kernel_supports(obj, FEAT_BTF_TYPE_TAG);
  bool has_enum64 = kernel_supports(obj, FEAT_BTF_ENUM64);
  int enum64_placeholder_id = 0;
  struct btf_type *t;
  int i, j, vlen;

  for (i = 1; i < btf__type_cnt(btf); i++) {
    t = (struct btf_type *)btf__type_by_id(btf, i);

    if ((!has_datasec && btf_is_var(t)) || (!has_decl_tag && btf_is_decl_tag(t))) {
      /* replace VAR/DECL_TAG with INT */
      t->info = BTF_INFO_ENC(BTF_KIND_INT, 0, 0);
      /*
       * using size = 1 is the safest choice, 4 will be too
       * big and cause kernel BTF validation failure if
       * original variable took less than 4 bytes
       */
      t->size = 1;
      *(int *)(t + 1) = BTF_INT_ENC(0, 0, 8);
    } else if (!has_datasec && btf_is_datasec(t)) {
      /* replace DATASEC with STRUCT */
      const struct btf_var_secinfo *v = btf_var_secinfos(t);
      struct btf_member *m = btf_members(t);
      struct btf_type *vt;
      char *name;

      name = (char *)btf__name_by_offset(btf, t->name_off);
      while (*name) {
        if (*name == '.')
          *name = '_';
        name++;
      }

      vlen = btf_vlen(t);
      t->info = BTF_INFO_ENC(BTF_KIND_STRUCT, 0, vlen);
      for (j = 0; j < vlen; j++, v++, m++) {
        /* order of field assignments is important */
        m->offset = v->offset * 8;
        m->type = v->type;
        /* preserve variable name as member name */
        vt = (void *)btf__type_by_id(btf, v->type);
        m->name_off = vt->name_off;
      }
    } else if (!has_func && btf_is_func_proto(t)) {
      /* replace FUNC_PROTO with ENUM */
      vlen = btf_vlen(t);
      t->info = BTF_INFO_ENC(BTF_KIND_ENUM, 0, vlen);
      t->size = sizeof(__u32); /* kernel enforced */
    } else if (!has_func && btf_is_func(t)) {
      /* replace FUNC with TYPEDEF */
      t->info = BTF_INFO_ENC(BTF_KIND_TYPEDEF, 0, 0);
    } else if (!has_func_global && btf_is_func(t)) {
      /* replace BTF_FUNC_GLOBAL with BTF_FUNC_STATIC */
      t->info = BTF_INFO_ENC(BTF_KIND_FUNC, 0, 0);
    } else if (!has_float && btf_is_float(t)) {
      /* replace FLOAT with an equally-sized empty STRUCT;
       * since C compilers do not accept e.g. "float" as a
       * valid struct name, make it anonymous
       */
      t->name_off = 0;
      t->info = BTF_INFO_ENC(BTF_KIND_STRUCT, 0, 0);
    } else if (!has_type_tag && btf_is_type_tag(t)) {
      /* replace TYPE_TAG with a CONST */
      t->name_off = 0;
      t->info = BTF_INFO_ENC(BTF_KIND_CONST, 0, 0);
    } else if (!has_enum64 && btf_is_enum(t)) {
      /* clear the kflag */
      t->info = btf_type_info(btf_kind(t), btf_vlen(t), false);
    } else if (!has_enum64 && btf_is_enum64(t)) {
      /* replace ENUM64 with a union */
      struct btf_member *m;

      if (enum64_placeholder_id == 0) {
        enum64_placeholder_id = btf__add_int(btf, "enum64_placeholder", 1, 0);
        if (enum64_placeholder_id < 0)
          return enum64_placeholder_id;

        t = (struct btf_type *)btf__type_by_id(btf, i);
      }

      m = btf_members(t);
      vlen = btf_vlen(t);
      t->info = BTF_INFO_ENC(BTF_KIND_UNION, 0, vlen);
      for (j = 0; j < vlen; j++, m++) {
        m->type = enum64_placeholder_id;
        m->offset = 0;
      }
    }
  }

  return 0;
}

static bool libbpf_needs_btf(const struct bpf_object *obj)
{
  return obj->efile.btf_maps_shndx >= 0 ||
         obj->efile.st_ops_shndx >= 0 ||
         obj->efile.st_ops_link_shndx >= 0 ||
         obj->nr_extern > 0;
}

static bool kernel_needs_btf(const struct bpf_object *obj)
{
  return obj->efile.st_ops_shndx >= 0 || obj->efile.st_ops_link_shndx >= 0;
}

static int bpf_object__init_btf(struct bpf_object *obj,
        Elf_Data *btf_data,
        Elf_Data *btf_ext_data)
{
  int err = -ENOENT;

  if (btf_data) {
    obj->btf = btf__new(btf_data->d_buf, btf_data->d_size);
    err = libbpf_get_error(obj->btf);
    if (err) {
      obj->btf = NULL;
      pr_warn("Error loading ELF section %s: %d.\n", BTF_ELF_SEC, err);
      goto out;
    }
    /* enforce 8-byte pointers for BPF-targeted BTFs */
    btf__set_pointer_size(obj->btf, 8);
  }
  if (btf_ext_data) {
    struct btf_ext_info *ext_segs[3];
    int seg_num, sec_num;

    if (!obj->btf) {
      pr_debug("Ignore ELF section %s because its depending ELF section %s is not found.\n",
         BTF_EXT_ELF_SEC, BTF_ELF_SEC);
      goto out;
    }
    obj->btf_ext = btf_ext__new(btf_ext_data->d_buf, btf_ext_data->d_size);
    err = libbpf_get_error(obj->btf_ext);
    if (err) {
      pr_warn("Error loading ELF section %s: %d. Ignored and continue.\n",
        BTF_EXT_ELF_SEC, err);
      obj->btf_ext = NULL;
      goto out;
    }

    /* setup .BTF.ext to ELF section mapping */
    ext_segs[0] = &obj->btf_ext->func_info;
    ext_segs[1] = &obj->btf_ext->line_info;
    ext_segs[2] = &obj->btf_ext->core_relo_info;
    for (seg_num = 0; seg_num < ARRAY_SIZE(ext_segs); seg_num++) {
      struct btf_ext_info *seg = ext_segs[seg_num];
      const struct btf_ext_info_sec *sec;
      const char *sec_name;
      Elf_Scn *scn;

      if (seg->sec_cnt == 0)
        continue;

      seg->sec_idxs = calloc(seg->sec_cnt, sizeof(*seg->sec_idxs));
      if (!seg->sec_idxs) {
        err = -ENOMEM;
        goto out;
      }

      sec_num = 0;
      for_each_btf_ext_sec(seg, sec) {
        /* preventively increment index to avoid doing
         * this before every continue below
         */
        sec_num++;

        sec_name = btf__name_by_offset(obj->btf, sec->sec_name_off);
        if (str_is_empty(sec_name))
          continue;
        scn = elf_sec_by_name(obj, sec_name);
        if (!scn)
          continue;

        seg->sec_idxs[sec_num - 1] = elf_ndxscn(scn);
      }
    }
  }
out:
  if (err && libbpf_needs_btf(obj)) {
    pr_warn("BTF is required, but is missing or corrupted.\n");
    return err;
  }
  return 0;
}

static int compare_vsi_off(const void *_a, const void *_b)
{
  const struct btf_var_secinfo *a = _a;
  const struct btf_var_secinfo *b = _b;

  return a->offset - b->offset;
}

static int btf_fixup_datasec(struct bpf_object *obj, struct btf *btf,
           struct btf_type *t)
{
  __u32 size = 0, i, vars = btf_vlen(t);
  const char *sec_name = btf__name_by_offset(btf, t->name_off);
  struct btf_var_secinfo *vsi;
  bool fixup_offsets = false;
  int err;

  if (!sec_name) {
    pr_debug("No name found in string section for DATASEC kind.\n");
    return -ENOENT;
  }

  /* Extern-backing datasecs (.ksyms, .kconfig) have their size and
   * variable offsets set at the previous step. Further, not every
   * extern BTF VAR has corresponding ELF symbol preserved, so we skip
   * all fixups altogether for such sections and go straight to sorting
   * VARs within their DATASEC.
   */
  if (strcmp(sec_name, KCONFIG_SEC) == 0 || strcmp(sec_name, KSYMS_SEC) == 0)
    goto sort_vars;

  /* Clang leaves DATASEC size and VAR offsets as zeroes, so we need to
   * fix this up. But BPF static linker already fixes this up and fills
   * all the sizes and offsets during static linking. So this step has
   * to be optional. But the STV_HIDDEN handling is non-optional for any
   * non-extern DATASEC, so the variable fixup loop below handles both
   * functions at the same time, paying the cost of BTF VAR <-> ELF
   * symbol matching just once.
   */
  if (t->size == 0) {
    err = find_elf_sec_sz(obj, sec_name, &size);
    if (err || !size) {
      pr_debug("sec '%s': failed to determine size from ELF: size %u, err %d\n",
         sec_name, size, err);
      return -ENOENT;
    }

    t->size = size;
    fixup_offsets = true;
  }

  for (i = 0, vsi = btf_var_secinfos(t); i < vars; i++, vsi++) {
    const struct btf_type *t_var;
    struct btf_var *var;
    const char *var_name;
    Elf64_Sym *sym;

    t_var = btf__type_by_id(btf, vsi->type);
    if (!t_var || !btf_is_var(t_var)) {
      pr_debug("sec '%s': unexpected non-VAR type found\n", sec_name);
      return -EINVAL;
    }

    var = btf_var(t_var);
    if (var->linkage == BTF_VAR_STATIC || var->linkage == BTF_VAR_GLOBAL_EXTERN)
      continue;

    var_name = btf__name_by_offset(btf, t_var->name_off);
    if (!var_name) {
      pr_debug("sec '%s': failed to find name of DATASEC's member #%d\n",
         sec_name, i);
      return -ENOENT;
    }

    sym = find_elf_var_sym(obj, var_name);
    if (IS_ERR(sym)) {
      pr_debug("sec '%s': failed to find ELF symbol for VAR '%s'\n",
         sec_name, var_name);
      return -ENOENT;
    }

    if (fixup_offsets)
      vsi->offset = sym->st_value;

    /* if variable is a global/weak symbol, but has restricted
     * (STV_HIDDEN or STV_INTERNAL) visibility, mark its BTF VAR
     * as static. This follows similar logic for functions (BPF
     * subprogs) and influences libbpf's further decisions about
     * whether to make global data BPF array maps as
     * BPF_F_MMAPABLE.
     */
    if (ELF64_ST_VISIBILITY(sym->st_other) == STV_HIDDEN
        || ELF64_ST_VISIBILITY(sym->st_other) == STV_INTERNAL)
      var->linkage = BTF_VAR_STATIC;
  }

sort_vars:
  qsort(btf_var_secinfos(t), vars, sizeof(*vsi), compare_vsi_off);
  return 0;
}

static int bpf_object_fixup_btf(struct bpf_object *obj)
{
  int i, n, err = 0;

  if (!obj->btf)
    return 0;

  n = btf__type_cnt(obj->btf);
  for (i = 1; i < n; i++) {
    struct btf_type *t = btf_type_by_id(obj->btf, i);

    /* Loader needs to fix up some of the things compiler
     * couldn't get its hands on while emitting BTF. This
     * is section size and global variable offset. We use
     * the info from the ELF itself for this purpose.
     */
    if (btf_is_datasec(t)) {
      err = btf_fixup_datasec(obj, obj->btf, t);
      if (err)
        return err;
    }
  }

  return 0;
}

static bool prog_needs_vmlinux_btf(struct bpf_program *prog)
{
  if (prog->type == BPF_PROG_TYPE_STRUCT_OPS ||
      prog->type == BPF_PROG_TYPE_LSM)
    return true;

  /* BPF_PROG_TYPE_TRACING programs which do not attach to other programs
   * also need vmlinux BTF
   */
  if (prog->type == BPF_PROG_TYPE_TRACING && !prog->attach_prog_fd)
    return true;

  return false;
}

static bool obj_needs_vmlinux_btf(const struct bpf_object *obj)
{
  struct bpf_program *prog;
  int i;

  /* CO-RE relocations need kernel BTF, only when btf_custom_path
   * is not specified
   */
  if (obj->btf_ext && obj->btf_ext->core_relo_info.len && !obj->btf_custom_path)
    return true;

  /* Support for typed ksyms needs kernel BTF */
  for (i = 0; i < obj->nr_extern; i++) {
    const struct extern_desc *ext;

    ext = &obj->externs[i];
    if (ext->type == EXT_KSYM && ext->ksym.type_id)
      return true;
  }

  bpf_object__for_each_program(prog, obj) {
    if (!prog->autoload)
      continue;
    if (prog_needs_vmlinux_btf(prog))
      return true;
  }

  return false;
}

static int bpf_object__load_vmlinux_btf(struct bpf_object *obj, bool force)
{
  int err;

  /* btf_vmlinux could be loaded earlier */
  if (obj->btf_vmlinux || obj->gen_loader)
    return 0;

  if (!force && !obj_needs_vmlinux_btf(obj))
    return 0;

  obj->btf_vmlinux = btf__load_vmlinux_btf();
  err = libbpf_get_error(obj->btf_vmlinux);
  if (err) {
    pr_warn("Error loading vmlinux BTF: %d\n", err);
    obj->btf_vmlinux = NULL;
    return err;
  }
  return 0;
}

static int bpf_object__sanitize_and_load_btf(struct bpf_object *obj)
{
  struct btf *kern_btf = obj->btf;
  bool btf_mandatory, sanitize;
  int i, err = 0;

  if (!obj->btf)
    return 0;

  if (!kernel_supports(obj, FEAT_BTF)) {
    if (kernel_needs_btf(obj)) {
      err = -EOPNOTSUPP;
      goto report;
    }
    pr_debug("Kernel doesn't support BTF, skipping uploading it.\n");
    return 0;
  }

  /* Even though some subprogs are global/weak, user might prefer more
   * permissive BPF verification process that BPF verifier performs for
   * static functions, taking into account more context from the caller
   * functions. In such case, they need to mark such subprogs with
   * __attribute__((visibility("hidden"))) and libbpf will adjust
   * corresponding FUNC BTF type to be marked as static and trigger more
   * involved BPF verification process.
   */
  for (i = 0; i < obj->nr_programs; i++) {
    struct bpf_program *prog = &obj->programs[i];
    struct btf_type *t;
    const char *name;
    int j, n;

    if (!prog->mark_btf_static || !prog_is_subprog(obj, prog))
      continue;

    n = btf__type_cnt(obj->btf);
    for (j = 1; j < n; j++) {
      t = btf_type_by_id(obj->btf, j);
      if (!btf_is_func(t) || btf_func_linkage(t) != BTF_FUNC_GLOBAL)
        continue;

      name = btf__str_by_offset(obj->btf, t->name_off);
      if (strcmp(name, prog->name) != 0)
        continue;

      t->info = btf_type_info(BTF_KIND_FUNC, BTF_FUNC_STATIC, 0);
      break;
    }
  }

  if (!kernel_supports(obj, FEAT_BTF_DECL_TAG))
    goto skip_exception_cb;
  for (i = 0; i < obj->nr_programs; i++) {
    struct bpf_program *prog = &obj->programs[i];
    int j, k, n;

    if (prog_is_subprog(obj, prog))
      continue;
    n = btf__type_cnt(obj->btf);
    for (j = 1; j < n; j++) {
      const char *str = "exception_callback:", *name;
      size_t len = strlen(str);
      struct btf_type *t;

      t = btf_type_by_id(obj->btf, j);
      if (!btf_is_decl_tag(t) || btf_decl_tag(t)->component_idx != -1)
        continue;

      name = btf__str_by_offset(obj->btf, t->name_off);
      if (strncmp(name, str, len))
        continue;

      t = btf_type_by_id(obj->btf, t->type);
      if (!btf_is_func(t) || btf_func_linkage(t) != BTF_FUNC_GLOBAL) {
        pr_warn("prog '%s': exception_callback:<value> decl tag not applied to the main program\n",
          prog->name);
        return -EINVAL;
      }
      if (strcmp(prog->name, btf__str_by_offset(obj->btf, t->name_off)))
        continue;
      /* Multiple callbacks are specified for the same prog,
       * the verifier will eventually return an error for this
       * case, hence simply skip appending a subprog.
       */
      if (prog->exception_cb_idx >= 0) {
        prog->exception_cb_idx = -1;
        break;
      }

      name += len;
      if (str_is_empty(name)) {
        pr_warn("prog '%s': exception_callback:<value> decl tag contains empty value\n",
          prog->name);
        return -EINVAL;
      }

      for (k = 0; k < obj->nr_programs; k++) {
        struct bpf_program *subprog = &obj->programs[k];

        if (!prog_is_subprog(obj, subprog))
          continue;
        if (strcmp(name, subprog->name))
          continue;
        /* Enforce non-hidden, as from verifier point of
         * view it expects global functions, whereas the
         * mark_btf_static fixes up linkage as static.
         */
        if (!subprog->sym_global || subprog->mark_btf_static) {
          pr_warn("prog '%s': exception callback %s must be a global non-hidden function\n",
            prog->name, subprog->name);
          return -EINVAL;
        }
        /* Let's see if we already saw a static exception callback with the same name */
        if (prog->exception_cb_idx >= 0) {
          pr_warn("prog '%s': multiple subprogs with same name as exception callback '%s'\n",
                  prog->name, subprog->name);
          return -EINVAL;
        }
        prog->exception_cb_idx = k;
        break;
      }

      if (prog->exception_cb_idx >= 0)
        continue;
      pr_warn("prog '%s': cannot find exception callback '%s'\n", prog->name, name);
      return -ENOENT;
    }
  }
skip_exception_cb:

  sanitize = btf_needs_sanitization(obj);
  if (sanitize) {
    const void *raw_data;
    __u32 sz;

    /* clone BTF to sanitize a copy and leave the original intact */
    raw_data = btf__raw_data(obj->btf, &sz);
    kern_btf = btf__new(raw_data, sz);
    err = libbpf_get_error(kern_btf);
    if (err)
      return err;

    /* enforce 8-byte pointers for BPF-targeted BTFs */
    btf__set_pointer_size(obj->btf, 8);
    err = bpf_object__sanitize_btf(obj, kern_btf);
    if (err)
      return err;
  }

  if (obj->gen_loader) {
    __u32 raw_size = 0;
    const void *raw_data = btf__raw_data(kern_btf, &raw_size);

    if (!raw_data)
      return -ENOMEM;
    bpf_gen__load_btf(obj->gen_loader, raw_data, raw_size);
    /* Pretend to have valid FD to pass various fd >= 0 checks.
     * This fd == 0 will not be used with any syscall and will be reset to -1 eventually.
     */
    btf__set_fd(kern_btf, 0);
  } else {
    /* currently BPF_BTF_LOAD only supports log_level 1 */
    err = btf_load_into_kernel(kern_btf, obj->log_buf, obj->log_size,
             obj->log_level ? 1 : 0);
  }
  if (sanitize) {
    if (!err) {
      /* move fd to libbpf's BTF */
      btf__set_fd(obj->btf, btf__fd(kern_btf));
      btf__set_fd(kern_btf, -1);
    }
    btf__free(kern_btf);
  }
report:
  if (err) {
    btf_mandatory = kernel_needs_btf(obj);
    pr_warn("Error loading .BTF into kernel: %d. %s\n", err,
      btf_mandatory ? "BTF is mandatory, can't proceed."
              : "BTF is optional, ignoring.");
    if (!btf_mandatory)
      err = 0;
  }
  return err;
}

static const char *elf_sym_str(const struct bpf_object *obj, size_t off)
{
  const char *name;

  name = elf_strptr(obj->efile.elf, obj->efile.strtabidx, off);
  if (!name) {
    pr_warn("elf: failed to get section name string at offset %zu from %s: %s\n",
      off, obj->path, elf_errmsg(-1));
    return NULL;
  }

  return name;
}

static const char *elf_sec_str(const struct bpf_object *obj, size_t off)
{
  const char *name;

  name = elf_strptr(obj->efile.elf, obj->efile.shstrndx, off);
  if (!name) {
    pr_warn("elf: failed to get section name string at offset %zu from %s: %s\n",
      off, obj->path, elf_errmsg(-1));
    return NULL;
  }

  return name;
}

static Elf_Scn *elf_sec_by_idx(const struct bpf_object *obj, size_t idx)
{
  Elf_Scn *scn;

  scn = elf_getscn(obj->efile.elf, idx);
  if (!scn) {
    pr_warn("elf: failed to get section(%zu) from %s: %s\n",
      idx, obj->path, elf_errmsg(-1));
    return NULL;
  }
  return scn;
}

static Elf_Scn *elf_sec_by_name(const struct bpf_object *obj, const char *name)
{
  Elf_Scn *scn = NULL;
  Elf *elf = obj->efile.elf;
  const char *sec_name;

  while ((scn = elf_nextscn(elf, scn)) != NULL) {
    sec_name = elf_sec_name(obj, scn);
    if (!sec_name)
      return NULL;

    if (strcmp(sec_name, name) != 0)
      continue;

    return scn;
  }
  return NULL;
}

static Elf64_Shdr *elf_sec_hdr(const struct bpf_object *obj, Elf_Scn *scn)
{
  Elf64_Shdr *shdr;

  if (!scn)
    return NULL;

  shdr = elf64_getshdr(scn);
  if (!shdr) {
    pr_warn("elf: failed to get section(%zu) header from %s: %s\n",
      elf_ndxscn(scn), obj->path, elf_errmsg(-1));
    return NULL;
  }

  return shdr;
}

static const char *elf_sec_name(const struct bpf_object *obj, Elf_Scn *scn)
{
  const char *name;
  Elf64_Shdr *sh;

  if (!scn)
    return NULL;

  sh = elf_sec_hdr(obj, scn);
  if (!sh)
    return NULL;

  name = elf_sec_str(obj, sh->sh_name);
  if (!name) {
    pr_warn("elf: failed to get section(%zu) name from %s: %s\n",
      elf_ndxscn(scn), obj->path, elf_errmsg(-1));
    return NULL;
  }

  return name;
}

static Elf_Data *elf_sec_data(const struct bpf_object *obj, Elf_Scn *scn)
{
  Elf_Data *data;

  if (!scn)
    return NULL;

  data = elf_getdata(scn, 0);
  if (!data) {
    pr_warn("elf: failed to get section(%zu) %s data from %s: %s\n",
      elf_ndxscn(scn), elf_sec_name(obj, scn) ?: "<?>",
      obj->path, elf_errmsg(-1));
    return NULL;
  }

  return data;
}

static Elf64_Sym *elf_sym_by_idx(const struct bpf_object *obj, size_t idx)
{
  if (idx >= obj->efile.symbols->d_size / sizeof(Elf64_Sym))
    return NULL;

  return (Elf64_Sym *)obj->efile.symbols->d_buf + idx;
}

static Elf64_Rel *elf_rel_by_idx(Elf_Data *data, size_t idx)
{
  if (idx >= data->d_size / sizeof(Elf64_Rel))
    return NULL;

  return (Elf64_Rel *)data->d_buf + idx;
}

static bool is_sec_name_dwarf(const char *name)
{
  /* approximation, but the actual list is too long */
  return str_has_pfx(name, ".debug_");
}

static bool ignore_elf_section(Elf64_Shdr *hdr, const char *name)
{
  /* no special handling of .strtab */
  if (hdr->sh_type == SHT_STRTAB)
    return true;

  /* ignore .llvm_addrsig section as well */
  if (hdr->sh_type == SHT_LLVM_ADDRSIG)
    return true;

  /* no subprograms will lead to an empty .text section, ignore it */
  if (hdr->sh_type == SHT_PROGBITS && hdr->sh_size == 0 &&
      strcmp(name, ".text") == 0)
    return true;

  /* DWARF sections */
  if (is_sec_name_dwarf(name))
    return true;

  if (str_has_pfx(name, ".rel")) {
    name += sizeof(".rel") - 1;
    /* DWARF section relocations */
    if (is_sec_name_dwarf(name))
      return true;

    /* .BTF and .BTF.ext don't need relocations */
    if (strcmp(name, BTF_ELF_SEC) == 0 ||
        strcmp(name, BTF_EXT_ELF_SEC) == 0)
      return true;
  }

  return false;
}

static int cmp_progs(const void *_a, const void *_b)
{
  const struct bpf_program *a = _a;
  const struct bpf_program *b = _b;

  if (a->sec_idx != b->sec_idx)
    return a->sec_idx < b->sec_idx ? -1 : 1;

  /* sec_insn_off can't be the same within the section */
  return a->sec_insn_off < b->sec_insn_off ? -1 : 1;
}

static int bpf_object__elf_collect(struct bpf_object *obj)
{
  struct elf_sec_desc *sec_desc;
  Elf *elf = obj->efile.elf;
  Elf_Data *btf_ext_data = NULL;
  Elf_Data *btf_data = NULL;
  int idx = 0, err = 0;
  const char *name;
  Elf_Data *data;
  Elf_Scn *scn;
  Elf64_Shdr *sh;

  /* ELF section indices are 0-based, but sec #0 is special "invalid"
   * section. Since section count retrieved by elf_getshdrnum() does
   * include sec #0, it is already the necessary size of an array to keep
   * all the sections.
   */
  if (elf_getshdrnum(obj->efile.elf, &obj->efile.sec_cnt)) {
    pr_warn("elf: failed to get the number of sections for %s: %s\n",
      obj->path, elf_errmsg(-1));
    return -LIBBPF_ERRNO__FORMAT;
  }
  obj->efile.secs = calloc(obj->efile.sec_cnt, sizeof(*obj->efile.secs));
  if (!obj->efile.secs)
    return -ENOMEM;

  /* a bunch of ELF parsing functionality depends on processing symbols,
   * so do the first pass and find the symbol table
   */
  scn = NULL;
  while ((scn = elf_nextscn(elf, scn)) != NULL) {
    sh = elf_sec_hdr(obj, scn);
    if (!sh)
      return -LIBBPF_ERRNO__FORMAT;

    if (sh->sh_type == SHT_SYMTAB) {
      if (obj->efile.symbols) {
        pr_warn("elf: multiple symbol tables in %s\n", obj->path);
        return -LIBBPF_ERRNO__FORMAT;
      }

      data = elf_sec_data(obj, scn);
      if (!data)
        return -LIBBPF_ERRNO__FORMAT;

      idx = elf_ndxscn(scn);

      obj->efile.symbols = data;
      obj->efile.symbols_shndx = idx;
      obj->efile.strtabidx = sh->sh_link;
    }
  }

  if (!obj->efile.symbols) {
    pr_warn("elf: couldn't find symbol table in %s, stripped object file?\n",
      obj->path);
    return -ENOENT;
  }

  scn = NULL;
  while ((scn = elf_nextscn(elf, scn)) != NULL) {
    idx = elf_ndxscn(scn);
    sec_desc = &obj->efile.secs[idx];

    sh = elf_sec_hdr(obj, scn);
    if (!sh)
      return -LIBBPF_ERRNO__FORMAT;

    name = elf_sec_str(obj, sh->sh_name);
    if (!name)
      return -LIBBPF_ERRNO__FORMAT;

    if (ignore_elf_section(sh, name))
      continue;

    data = elf_sec_data(obj, scn);
    if (!data)
      return -LIBBPF_ERRNO__FORMAT;

    pr_debug("elf: section(%d) %s, size %ld, link %d, flags %lx, type=%d\n",
       idx, name, (unsigned long)data->d_size,
       (int)sh->sh_link, (unsigned long)sh->sh_flags,
       (int)sh->sh_type);

    if (strcmp(name, "license") == 0) {
      err = bpf_object__init_license(obj, data->d_buf, data->d_size);
      if (err)
        return err;
    } else if (strcmp(name, "version") == 0) {
      err = bpf_object__init_kversion(obj, data->d_buf, data->d_size);
      if (err)
        return err;
    } else if (strcmp(name, "maps") == 0) {
      pr_warn("elf: legacy map definitions in 'maps' section are not supported by libbpf v1.0+\n");
      return -ENOTSUP;
    } else if (strcmp(name, MAPS_ELF_SEC) == 0) {
      obj->efile.btf_maps_shndx = idx;
    } else if (strcmp(name, BTF_ELF_SEC) == 0) {
      if (sh->sh_type != SHT_PROGBITS)
        return -LIBBPF_ERRNO__FORMAT;
      btf_data = data;
    } else if (strcmp(name, BTF_EXT_ELF_SEC) == 0) {
      if (sh->sh_type != SHT_PROGBITS)
        return -LIBBPF_ERRNO__FORMAT;
      btf_ext_data = data;
    } else if (sh->sh_type == SHT_SYMTAB) {
      /* already processed during the first pass above */
    } else if (sh->sh_type == SHT_PROGBITS && data->d_size > 0) {
      if (sh->sh_flags & SHF_EXECINSTR) {
        if (strcmp(name, ".text") == 0)
          obj->efile.text_shndx = idx;
        err = bpf_object__add_programs(obj, data, name, idx);
        if (err)
          return err;
      } else if (strcmp(name, DATA_SEC) == 0 ||
           str_has_pfx(name, DATA_SEC ".")) {
        sec_desc->sec_type = SEC_DATA;
        sec_desc->shdr = sh;
        sec_desc->data = data;
      } else if (strcmp(name, RODATA_SEC) == 0 ||
           str_has_pfx(name, RODATA_SEC ".")) {
        sec_desc->sec_type = SEC_RODATA;
        sec_desc->shdr = sh;
        sec_desc->data = data;
      } else if (strcmp(name, STRUCT_OPS_SEC) == 0) {
        obj->efile.st_ops_data = data;
        obj->efile.st_ops_shndx = idx;
      } else if (strcmp(name, STRUCT_OPS_LINK_SEC) == 0) {
        obj->efile.st_ops_link_data = data;
        obj->efile.st_ops_link_shndx = idx;
      } else {
        pr_info("elf: skipping unrecognized data section(%d) %s\n",
          idx, name);
      }
    } else if (sh->sh_type == SHT_REL) {
      int targ_sec_idx = sh->sh_info; /* points to other section */

      if (sh->sh_entsize != sizeof(Elf64_Rel) ||
          targ_sec_idx >= obj->efile.sec_cnt)
        return -LIBBPF_ERRNO__FORMAT;

      /* Only do relo for section with exec instructions */
      if (!section_have_execinstr(obj, targ_sec_idx) &&
          strcmp(name, ".rel" STRUCT_OPS_SEC) &&
          strcmp(name, ".rel" STRUCT_OPS_LINK_SEC) &&
          strcmp(name, ".rel" MAPS_ELF_SEC)) {
        pr_info("elf: skipping relo section(%d) %s for section(%d) %s\n",
          idx, name, targ_sec_idx,
          elf_sec_name(obj, elf_sec_by_idx(obj, targ_sec_idx)) ?: "<?>");
        continue;
      }

      sec_desc->sec_type = SEC_RELO;
      sec_desc->shdr = sh;
      sec_desc->data = data;
    } else if (sh->sh_type == SHT_NOBITS && (strcmp(name, BSS_SEC) == 0 ||
               str_has_pfx(name, BSS_SEC "."))) {
      sec_desc->sec_type = SEC_BSS;
      sec_desc->shdr = sh;
      sec_desc->data = data;
    } else {
      pr_info("elf: skipping section(%d) %s (size %zu)\n", idx, name,
        (size_t)sh->sh_size);
    }
  }

  if (!obj->efile.strtabidx || obj->efile.strtabidx > idx) {
    pr_warn("elf: symbol strings section missing or invalid in %s\n", obj->path);
    return -LIBBPF_ERRNO__FORMAT;
  }

  /* sort BPF programs by section name and in-section instruction offset
   * for faster search
   */
  if (obj->nr_programs)
    qsort(obj->programs, obj->nr_programs, sizeof(*obj->programs), cmp_progs);

  return bpf_object__init_btf(obj, btf_data, btf_ext_data);
}

static bool sym_is_extern(const Elf64_Sym *sym)
{
  int bind = ELF64_ST_BIND(sym->st_info);
  /* externs are symbols w/ type=NOTYPE, bind=GLOBAL|WEAK, section=UND */
  return sym->st_shndx == SHN_UNDEF &&
         (bind == STB_GLOBAL || bind == STB_WEAK) &&
         ELF64_ST_TYPE(sym->st_info) == STT_NOTYPE;
}

static bool sym_is_subprog(const Elf64_Sym *sym, int text_shndx)
{
  int bind = ELF64_ST_BIND(sym->st_info);
  int type = ELF64_ST_TYPE(sym->st_info);

  /* in .text section */
  if (sym->st_shndx != text_shndx)
    return false;

  /* local function */
  if (bind == STB_LOCAL && type == STT_SECTION)
    return true;

  /* global function */
  return bind == STB_GLOBAL && type == STT_FUNC;
}

static int find_extern_btf_id(const struct btf *btf, const char *ext_name)
{
  const struct btf_type *t;
  const char *tname;
  int i, n;

  if (!btf)
    return -ESRCH;

  n = btf__type_cnt(btf);
  for (i = 1; i < n; i++) {
    t = btf__type_by_id(btf, i);

    if (!btf_is_var(t) && !btf_is_func(t))
      continue;

    tname = btf__name_by_offset(btf, t->name_off);
    if (strcmp(tname, ext_name))
      continue;

    if (btf_is_var(t) &&
        btf_var(t)->linkage != BTF_VAR_GLOBAL_EXTERN)
      return -EINVAL;

    if (btf_is_func(t) && btf_func_linkage(t) != BTF_FUNC_EXTERN)
      return -EINVAL;

    return i;
  }

  return -ENOENT;
}

static int find_extern_sec_btf_id(struct btf *btf, int ext_btf_id) {
  const struct btf_var_secinfo *vs;
  const struct btf_type *t;
  int i, j, n;

  if (!btf)
    return -ESRCH;

  n = btf__type_cnt(btf);
  for (i = 1; i < n; i++) {
    t = btf__type_by_id(btf, i);

    if (!btf_is_datasec(t))
      continue;

    vs = btf_var_secinfos(t);
    for (j = 0; j < btf_vlen(t); j++, vs++) {
      if (vs->type == ext_btf_id)
        return i;
    }
  }

  return -ENOENT;
}

static enum kcfg_type find_kcfg_type(const struct btf *btf, int id,
             bool *is_signed)
{
  const struct btf_type *t;
  const char *name;

  t = skip_mods_and_typedefs(btf, id, NULL);
  name = btf__name_by_offset(btf, t->name_off);

  if (is_signed)
    *is_signed = false;
  switch (btf_kind(t)) {
  case BTF_KIND_INT: {
    int enc = btf_int_encoding(t);

    if (enc & BTF_INT_BOOL)
      return t->size == 1 ? KCFG_BOOL : KCFG_UNKNOWN;
    if (is_signed)
      *is_signed = enc & BTF_INT_SIGNED;
    if (t->size == 1)
      return KCFG_CHAR;
    if (t->size < 1 || t->size > 8 || (t->size & (t->size - 1)))
      return KCFG_UNKNOWN;
    return KCFG_INT;
  }
  case BTF_KIND_ENUM:
    if (t->size != 4)
      return KCFG_UNKNOWN;
    if (strcmp(name, "libbpf_tristate"))
      return KCFG_UNKNOWN;
    return KCFG_TRISTATE;
  case BTF_KIND_ENUM64:
    if (strcmp(name, "libbpf_tristate"))
      return KCFG_UNKNOWN;
    return KCFG_TRISTATE;
  case BTF_KIND_ARRAY:
    if (btf_array(t)->nelems == 0)
      return KCFG_UNKNOWN;
    if (find_kcfg_type(btf, btf_array(t)->type, NULL) != KCFG_CHAR)
      return KCFG_UNKNOWN;
    return KCFG_CHAR_ARR;
  default:
    return KCFG_UNKNOWN;
  }
}

static int cmp_externs(const void *_a, const void *_b)
{
  const struct extern_desc *a = _a;
  const struct extern_desc *b = _b;

  if (a->type != b->type)
    return a->type < b->type ? -1 : 1;

  if (a->type == EXT_KCFG) {
    /* descending order by alignment requirements */
    if (a->kcfg.align != b->kcfg.align)
      return a->kcfg.align > b->kcfg.align ? -1 : 1;
    /* ascending order by size, within same alignment class */
    if (a->kcfg.sz != b->kcfg.sz)
      return a->kcfg.sz < b->kcfg.sz ? -1 : 1;
  }

  /* resolve ties by name */
  return strcmp(a->name, b->name);
}

static int find_int_btf_id(const struct btf *btf)
{
  const struct btf_type *t;
  int i, n;

  n = btf__type_cnt(btf);
  for (i = 1; i < n; i++) {
    t = btf__type_by_id(btf, i);

    if (btf_is_int(t) && btf_int_bits(t) == 32)
      return i;
  }

  return 0;
}

static int add_dummy_ksym_var(struct btf *btf)
{
  int i, int_btf_id, sec_btf_id, dummy_var_btf_id;
  const struct btf_var_secinfo *vs;
  const struct btf_type *sec;

  if (!btf)
    return 0;

  sec_btf_id = btf__find_by_name_kind(btf, KSYMS_SEC,
              BTF_KIND_DATASEC);
  if (sec_btf_id < 0)
    return 0;

  sec = btf__type_by_id(btf, sec_btf_id);
  vs = btf_var_secinfos(sec);
  for (i = 0; i < btf_vlen(sec); i++, vs++) {
    const struct btf_type *vt;

    vt = btf__type_by_id(btf, vs->type);
    if (btf_is_func(vt))
      break;
  }

  /* No func in ksyms sec.  No need to add dummy var. */
  if (i == btf_vlen(sec))
    return 0;

  int_btf_id = find_int_btf_id(btf);
  dummy_var_btf_id = btf__add_var(btf,
          "dummy_ksym",
          BTF_VAR_GLOBAL_ALLOCATED,
          int_btf_id);
  if (dummy_var_btf_id < 0)
    pr_warn("cannot create a dummy_ksym var\n");

  return dummy_var_btf_id;
}

static int bpf_object__collect_externs(struct bpf_object *obj)
{
  struct btf_type *sec, *kcfg_sec = NULL, *ksym_sec = NULL;
  const struct btf_type *t;
  struct extern_desc *ext;
  int i, n, off, dummy_var_btf_id;
  const char *ext_name, *sec_name;
  size_t ext_essent_len;
  Elf_Scn *scn;
  Elf64_Shdr *sh;

  if (!obj->efile.symbols)
    return 0;

  scn = elf_sec_by_idx(obj, obj->efile.symbols_shndx);
  sh = elf_sec_hdr(obj, scn);
  if (!sh || sh->sh_entsize != sizeof(Elf64_Sym))
    return -LIBBPF_ERRNO__FORMAT;

  dummy_var_btf_id = add_dummy_ksym_var(obj->btf);
  if (dummy_var_btf_id < 0)
    return dummy_var_btf_id;

  n = sh->sh_size / sh->sh_entsize;
  pr_debug("looking for externs among %d symbols...\n", n);

  for (i = 0; i < n; i++) {
    Elf64_Sym *sym = elf_sym_by_idx(obj, i);

    if (!sym)
      return -LIBBPF_ERRNO__FORMAT;
    if (!sym_is_extern(sym))
      continue;
    ext_name = elf_sym_str(obj, sym->st_name);
    if (!ext_name || !ext_name[0])
      continue;

    ext = obj->externs;
    ext = libbpf_reallocarray(ext, obj->nr_extern + 1, sizeof(*ext));
    if (!ext)
      return -ENOMEM;
    obj->externs = ext;
    ext = &ext[obj->nr_extern];
    memset(ext, 0, sizeof(*ext));
    obj->nr_extern++;

    ext->btf_id = find_extern_btf_id(obj->btf, ext_name);
    if (ext->btf_id <= 0) {
      pr_warn("failed to find BTF for extern '%s': %d\n",
        ext_name, ext->btf_id);
      return ext->btf_id;
    }
    t = btf__type_by_id(obj->btf, ext->btf_id);
    ext->name = btf__name_by_offset(obj->btf, t->name_off);
    ext->sym_idx = i;
    ext->is_weak = ELF64_ST_BIND(sym->st_info) == STB_WEAK;

    ext_essent_len = bpf_core_essential_name_len(ext->name);
    ext->essent_name = NULL;
    if (ext_essent_len != strlen(ext->name)) {
      ext->essent_name = strndup(ext->name, ext_essent_len);
      if (!ext->essent_name)
        return -ENOMEM;
    }

    ext->sec_btf_id = find_extern_sec_btf_id(obj->btf, ext->btf_id);
    if (ext->sec_btf_id <= 0) {
      pr_warn("failed to find BTF for extern '%s' [%d] section: %d\n",
        ext_name, ext->btf_id, ext->sec_btf_id);
      return ext->sec_btf_id;
    }
    sec = (void *)btf__type_by_id(obj->btf, ext->sec_btf_id);
    sec_name = btf__name_by_offset(obj->btf, sec->name_off);

    if (strcmp(sec_name, KCONFIG_SEC) == 0) {
      if (btf_is_func(t)) {
        pr_warn("extern function %s is unsupported under %s section\n",
          ext->name, KCONFIG_SEC);
        return -ENOTSUP;
      }
      kcfg_sec = sec;
      ext->type = EXT_KCFG;
      ext->kcfg.sz = btf__resolve_size(obj->btf, t->type);
      if (ext->kcfg.sz <= 0) {
        pr_warn("failed to resolve size of extern (kcfg) '%s': %d\n",
          ext_name, ext->kcfg.sz);
        return ext->kcfg.sz;
      }
      ext->kcfg.align = btf__align_of(obj->btf, t->type);
      if (ext->kcfg.align <= 0) {
        pr_warn("failed to determine alignment of extern (kcfg) '%s': %d\n",
          ext_name, ext->kcfg.align);
        return -EINVAL;
      }
      ext->kcfg.type = find_kcfg_type(obj->btf, t->type,
              &ext->kcfg.is_signed);
      if (ext->kcfg.type == KCFG_UNKNOWN) {
        pr_warn("extern (kcfg) '%s': type is unsupported\n", ext_name);
        return -ENOTSUP;
      }
    } else if (strcmp(sec_name, KSYMS_SEC) == 0) {
      ksym_sec = sec;
      ext->type = EXT_KSYM;
      skip_mods_and_typedefs(obj->btf, t->type,
                 &ext->ksym.type_id);
    } else {
      pr_warn("unrecognized extern section '%s'\n", sec_name);
      return -ENOTSUP;
    }
  }
  pr_debug("collected %d externs total\n", obj->nr_extern);

  if (!obj->nr_extern)
    return 0;

  /* sort externs by type, for kcfg ones also by (align, size, name) */
  qsort(obj->externs, obj->nr_extern, sizeof(*ext), cmp_externs);

  /* for .ksyms section, we need to turn all externs into allocated
   * variables in BTF to pass kernel verification; we do this by
   * pretending that each extern is a 8-byte variable
   */
  if (ksym_sec) {
    /* find existing 4-byte integer type in BTF to use for fake
     * extern variables in DATASEC
     */
    int int_btf_id = find_int_btf_id(obj->btf);
    /* For extern function, a dummy_var added earlier
     * will be used to replace the vs->type and
     * its name string will be used to refill
     * the missing param's name.
     */
    const struct btf_type *dummy_var;

    dummy_var = btf__type_by_id(obj->btf, dummy_var_btf_id);
    for (i = 0; i < obj->nr_extern; i++) {
      ext = &obj->externs[i];
      if (ext->type != EXT_KSYM)
        continue;
      pr_debug("extern (ksym) #%d: symbol %d, name %s\n",
         i, ext->sym_idx, ext->name);
    }

    sec = ksym_sec;
    n = btf_vlen(sec);
    for (i = 0, off = 0; i < n; i++, off += sizeof(int)) {
      struct btf_var_secinfo *vs = btf_var_secinfos(sec) + i;
      struct btf_type *vt;

      vt = (void *)btf__type_by_id(obj->btf, vs->type);
      ext_name = btf__name_by_offset(obj->btf, vt->name_off);
      ext = find_extern_by_name(obj, ext_name);
      if (!ext) {
        pr_warn("failed to find extern definition for BTF %s '%s'\n",
          btf_kind_str(vt), ext_name);
        return -ESRCH;
      }
      if (btf_is_func(vt)) {
        const struct btf_type *func_proto;
        struct btf_param *param;
        int j;

        func_proto = btf__type_by_id(obj->btf,
                   vt->type);
        param = btf_params(func_proto);
        /* Reuse the dummy_var string if the
         * func proto does not have param name.
         */
        for (j = 0; j < btf_vlen(func_proto); j++)
          if (param[j].type && !param[j].name_off)
            param[j].name_off =
              dummy_var->name_off;
        vs->type = dummy_var_btf_id;
        vt->info &= ~0xffff;
        vt->info |= BTF_FUNC_GLOBAL;
      } else {
        btf_var(vt)->linkage = BTF_VAR_GLOBAL_ALLOCATED;
        vt->type = int_btf_id;
      }
      vs->offset = off;
      vs->size = sizeof(int);
    }
    sec->size = off;
  }

  if (kcfg_sec) {
    sec = kcfg_sec;
    /* for kcfg externs calculate their offsets within a .kconfig map */
    off = 0;
    for (i = 0; i < obj->nr_extern; i++) {
      ext = &obj->externs[i];
      if (ext->type != EXT_KCFG)
        continue;

      ext->kcfg.data_off = roundup(off, ext->kcfg.align);
      off = ext->kcfg.data_off + ext->kcfg.sz;
      pr_debug("extern (kcfg) #%d: symbol %d, off %u, name %s\n",
         i, ext->sym_idx, ext->kcfg.data_off, ext->name);
    }
    sec->size = off;
    n = btf_vlen(sec);
    for (i = 0; i < n; i++) {
      struct btf_var_secinfo *vs = btf_var_secinfos(sec) + i;

      t = btf__type_by_id(obj->btf, vs->type);
      ext_name = btf__name_by_offset(obj->btf, t->name_off);
      ext = find_extern_by_name(obj, ext_name);
      if (!ext) {
        pr_warn("failed to find extern definition for BTF var '%s'\n",
          ext_name);
        return -ESRCH;
      }
      btf_var(t)->linkage = BTF_VAR_GLOBAL_ALLOCATED;
      vs->offset = ext->kcfg.data_off;
    }
  }
  return 0;
}

static bool prog_is_subprog(const struct bpf_object *obj, const struct bpf_program *prog)
{
  return prog->sec_idx == obj->efile.text_shndx && obj->nr_programs > 1;
}

struct bpf_program *
bpf_object__find_program_by_name(const struct bpf_object *obj,
         const char *name)
{
  struct bpf_program *prog;

  bpf_object__for_each_program(prog, obj) {
    if (prog_is_subprog(obj, prog))
      continue;
    if (!strcmp(prog->name, name))
      return prog;
  }
  return errno = ENOENT, NULL;
}

static bool bpf_object__shndx_is_data(const struct bpf_object *obj,
              int shndx)
{
  switch (obj->efile.secs[shndx].sec_type) {
  case SEC_BSS:
  case SEC_DATA:
  case SEC_RODATA:
    return true;
  default:
    return false;
  }
}

static bool bpf_object__shndx_is_maps(const struct bpf_object *obj,
              int shndx)
{
  return shndx == obj->efile.btf_maps_shndx;
}

static enum libbpf_map_type
bpf_object__section_to_libbpf_map_type(const struct bpf_object *obj, int shndx)
{
  if (shndx == obj->efile.symbols_shndx)
    return LIBBPF_MAP_KCONFIG;

  switch (obj->efile.secs[shndx].sec_type) {
  case SEC_BSS:
    return LIBBPF_MAP_BSS;
  case SEC_DATA:
    return LIBBPF_MAP_DATA;
  case SEC_RODATA:
    return LIBBPF_MAP_RODATA;
  default:
    return LIBBPF_MAP_UNSPEC;
  }
}

static int bpf_program__record_reloc(struct bpf_program *prog,
             struct reloc_desc *reloc_desc,
             __u32 insn_idx, const char *sym_name,
             const Elf64_Sym *sym, const Elf64_Rel *rel)
{
  struct bpf_insn *insn = &prog->insns[insn_idx];
  size_t map_idx, nr_maps = prog->obj->nr_maps;
  struct bpf_object *obj = prog->obj;
  __u32 shdr_idx = sym->st_shndx;
  enum libbpf_map_type type;
  const char *sym_sec_name;
  struct bpf_map *map;

  if (!is_call_insn(insn) && !is_ldimm64_insn(insn)) {
    pr_warn("prog '%s': invalid relo against '%s' for insns[%d].code 0x%x\n",
      prog->name, sym_name, insn_idx, insn->code);
    return -LIBBPF_ERRNO__RELOC;
  }

  if (sym_is_extern(sym)) {
    int sym_idx = ELF64_R_SYM(rel->r_info);
    int i, n = obj->nr_extern;
    struct extern_desc *ext;

    for (i = 0; i < n; i++) {
      ext = &obj->externs[i];
      if (ext->sym_idx == sym_idx)
        break;
    }
    if (i >= n) {
      pr_warn("prog '%s': extern relo failed to find extern for '%s' (%d)\n",
        prog->name, sym_name, sym_idx);
      return -LIBBPF_ERRNO__RELOC;
    }
    pr_debug("prog '%s': found extern #%d '%s' (sym %d) for insn #%u\n",
       prog->name, i, ext->name, ext->sym_idx, insn_idx);
    if (insn->code == (BPF_JMP | BPF_CALL))
      reloc_desc->type = RELO_EXTERN_CALL;
    else
      reloc_desc->type = RELO_EXTERN_LD64;
    reloc_desc->insn_idx = insn_idx;
    reloc_desc->ext_idx = i;
    return 0;
  }

  /* sub-program call relocation */
  if (is_call_insn(insn)) {
    if (insn->src_reg != BPF_PSEUDO_CALL) {
      pr_warn("prog '%s': incorrect bpf_call opcode\n", prog->name);
      return -LIBBPF_ERRNO__RELOC;
    }
    /* text_shndx can be 0, if no default "main" program exists */
    if (!shdr_idx || shdr_idx != obj->efile.text_shndx) {
      sym_sec_name = elf_sec_name(obj, elf_sec_by_idx(obj, shdr_idx));
      pr_warn("prog '%s': bad call relo against '%s' in section '%s'\n",
        prog->name, sym_name, sym_sec_name);
      return -LIBBPF_ERRNO__RELOC;
    }
    if (sym->st_value % BPF_INSN_SZ) {
      pr_warn("prog '%s': bad call relo against '%s' at offset %zu\n",
        prog->name, sym_name, (size_t)sym->st_value);
      return -LIBBPF_ERRNO__RELOC;
    }
    reloc_desc->type = RELO_CALL;
    reloc_desc->insn_idx = insn_idx;
    reloc_desc->sym_off = sym->st_value;
    return 0;
  }

  if (!shdr_idx || shdr_idx >= SHN_LORESERVE) {
    pr_warn("prog '%s': invalid relo against '%s' in special section 0x%x; forgot to initialize global var?..\n",
      prog->name, sym_name, shdr_idx);
    return -LIBBPF_ERRNO__RELOC;
  }

  /* loading subprog addresses */
  if (sym_is_subprog(sym, obj->efile.text_shndx)) {
    /* global_func: sym->st_value = offset in the section, insn->imm = 0.
     * local_func: sym->st_value = 0, insn->imm = offset in the section.
     */
    if ((sym->st_value % BPF_INSN_SZ) || (insn->imm % BPF_INSN_SZ)) {
      pr_warn("prog '%s': bad subprog addr relo against '%s' at offset %zu+%d\n",
        prog->name, sym_name, (size_t)sym->st_value, insn->imm);
      return -LIBBPF_ERRNO__RELOC;
    }

    reloc_desc->type = RELO_SUBPROG_ADDR;
    reloc_desc->insn_idx = insn_idx;
    reloc_desc->sym_off = sym->st_value;
    return 0;
  }

  type = bpf_object__section_to_libbpf_map_type(obj, shdr_idx);
  sym_sec_name = elf_sec_name(obj, elf_sec_by_idx(obj, shdr_idx));

  /* generic map reference relocation */
  if (type == LIBBPF_MAP_UNSPEC) {
    if (!bpf_object__shndx_is_maps(obj, shdr_idx)) {
      pr_warn("prog '%s': bad map relo against '%s' in section '%s'\n",
        prog->name, sym_name, sym_sec_name);
      return -LIBBPF_ERRNO__RELOC;
    }
    for (map_idx = 0; map_idx < nr_maps; map_idx++) {
      map = &obj->maps[map_idx];
      if (map->libbpf_type != type ||
          map->sec_idx != sym->st_shndx ||
          map->sec_offset != sym->st_value)
        continue;
      pr_debug("prog '%s': found map %zd (%s, sec %d, off %zu) for insn #%u\n",
         prog->name, map_idx, map->name, map->sec_idx,
         map->sec_offset, insn_idx);
      break;
    }
    if (map_idx >= nr_maps) {
      pr_warn("prog '%s': map relo failed to find map for section '%s', off %zu\n",
        prog->name, sym_sec_name, (size_t)sym->st_value);
      return -LIBBPF_ERRNO__RELOC;
    }
    reloc_desc->type = RELO_LD64;
    reloc_desc->insn_idx = insn_idx;
    reloc_desc->map_idx = map_idx;
    reloc_desc->sym_off = 0; /* sym->st_value determines map_idx */
    return 0;
  }

  /* global data map relocation */
  if (!bpf_object__shndx_is_data(obj, shdr_idx)) {
    pr_warn("prog '%s': bad data relo against section '%s'\n",
      prog->name, sym_sec_name);
    return -LIBBPF_ERRNO__RELOC;
  }
  for (map_idx = 0; map_idx < nr_maps; map_idx++) {
    map = &obj->maps[map_idx];
    if (map->libbpf_type != type || map->sec_idx != sym->st_shndx)
      continue;
    pr_debug("prog '%s': found data map %zd (%s, sec %d, off %zu) for insn %u\n",
       prog->name, map_idx, map->name, map->sec_idx,
       map->sec_offset, insn_idx);
    break;
  }
  if (map_idx >= nr_maps) {
    pr_warn("prog '%s': data relo failed to find map for section '%s'\n",
      prog->name, sym_sec_name);
    return -LIBBPF_ERRNO__RELOC;
  }

  reloc_desc->type = RELO_DATA;
  reloc_desc->insn_idx = insn_idx;
  reloc_desc->map_idx = map_idx;
  reloc_desc->sym_off = sym->st_value;
  return 0;
}

static bool prog_contains_insn(const struct bpf_program *prog, size_t insn_idx)
{
  return insn_idx >= prog->sec_insn_off &&
         insn_idx < prog->sec_insn_off + prog->sec_insn_cnt;
}

static struct bpf_program *find_prog_by_sec_insn(const struct bpf_object *obj,
             size_t sec_idx, size_t insn_idx)
{
  int l = 0, r = obj->nr_programs - 1, m;
  struct bpf_program *prog;

  if (!obj->nr_programs)
    return NULL;

  while (l < r) {
    m = l + (r - l + 1) / 2;
    prog = &obj->programs[m];

    if (prog->sec_idx < sec_idx ||
        (prog->sec_idx == sec_idx && prog->sec_insn_off <= insn_idx))
      l = m;
    else
      r = m - 1;
  }
  /* matching program could be at index l, but it still might be the
   * wrong one, so we need to double check conditions for the last time
   */
  prog = &obj->programs[l];
  if (prog->sec_idx == sec_idx && prog_contains_insn(prog, insn_idx))
    return prog;
  return NULL;
}

static int
bpf_object__collect_prog_relos(struct bpf_object *obj, Elf64_Shdr *shdr, Elf_Data *data)
{
  const char *relo_sec_name, *sec_name;
  size_t sec_idx = shdr->sh_info, sym_idx;
  struct bpf_program *prog;
  struct reloc_desc *relos;
  int err, i, nrels;
  const char *sym_name;
  __u32 insn_idx;
  Elf_Scn *scn;
  Elf_Data *scn_data;
  Elf64_Sym *sym;
  Elf64_Rel *rel;

  if (sec_idx >= obj->efile.sec_cnt)
    return -EINVAL;

  scn = elf_sec_by_idx(obj, sec_idx);
  scn_data = elf_sec_data(obj, scn);

  relo_sec_name = elf_sec_str(obj, shdr->sh_name);
  sec_name = elf_sec_name(obj, scn);
  if (!relo_sec_name || !sec_name)
    return -EINVAL;

  pr_debug("sec '%s': collecting relocation for section(%zu) '%s'\n",
     relo_sec_name, sec_idx, sec_name);
  nrels = shdr->sh_size / shdr->sh_entsize;

  for (i = 0; i < nrels; i++) {
    rel = elf_rel_by_idx(data, i);
    if (!rel) {
      pr_warn("sec '%s': failed to get relo #%d\n", relo_sec_name, i);
      return -LIBBPF_ERRNO__FORMAT;
    }

    sym_idx = ELF64_R_SYM(rel->r_info);
    sym = elf_sym_by_idx(obj, sym_idx);
    if (!sym) {
      pr_warn("sec '%s': symbol #%zu not found for relo #%d\n",
        relo_sec_name, sym_idx, i);
      return -LIBBPF_ERRNO__FORMAT;
    }

    if (sym->st_shndx >= obj->efile.sec_cnt) {
      pr_warn("sec '%s': corrupted symbol #%zu pointing to invalid section #%zu for relo #%d\n",
        relo_sec_name, sym_idx, (size_t)sym->st_shndx, i);
      return -LIBBPF_ERRNO__FORMAT;
    }

    if (rel->r_offset % BPF_INSN_SZ || rel->r_offset >= scn_data->d_size) {
      pr_warn("sec '%s': invalid offset 0x%zx for relo #%d\n",
        relo_sec_name, (size_t)rel->r_offset, i);
      return -LIBBPF_ERRNO__FORMAT;
    }

    insn_idx = rel->r_offset / BPF_INSN_SZ;
    /* relocations against static functions are recorded as
     * relocations against the section that contains a function;
     * in such case, symbol will be STT_SECTION and sym.st_name
     * will point to empty string (0), so fetch section name
     * instead
     */
    if (ELF64_ST_TYPE(sym->st_info) == STT_SECTION && sym->st_name == 0)
      sym_name = elf_sec_name(obj, elf_sec_by_idx(obj, sym->st_shndx));
    else
      sym_name = elf_sym_str(obj, sym->st_name);
    sym_name = sym_name ?: "<?";

    pr_debug("sec '%s': relo #%d: insn #%u against '%s'\n",
       relo_sec_name, i, insn_idx, sym_name);

    prog = find_prog_by_sec_insn(obj, sec_idx, insn_idx);
    if (!prog) {
      pr_debug("sec '%s': relo #%d: couldn't find program in section '%s' for insn #%u, probably overridden weak function, skipping...\n",
        relo_sec_name, i, sec_name, insn_idx);
      continue;
    }

    relos = libbpf_reallocarray(prog->reloc_desc,
              prog->nr_reloc + 1, sizeof(*relos));
    if (!relos)
      return -ENOMEM;
    prog->reloc_desc = relos;

    /* adjust insn_idx to local BPF program frame of reference */
    insn_idx -= prog->sec_insn_off;
    err = bpf_program__record_reloc(prog, &relos[prog->nr_reloc],
            insn_idx, sym_name, sym, rel);
    if (err)
      return err;

    prog->nr_reloc++;
  }
  return 0;
}

static int map_fill_btf_type_info(struct bpf_object *obj, struct bpf_map *map)
{
  int id;

  if (!obj->btf)
    return -ENOENT;

  /* if it's BTF-defined map, we don't need to search for type IDs.
   * For struct_ops map, it does not need btf_key_type_id and
   * btf_value_type_id.
   */
  if (map->sec_idx == obj->efile.btf_maps_shndx || bpf_map__is_struct_ops(map))
    return 0;

  /*
   * LLVM annotates global data differently in BTF, that is,
   * only as '.data', '.bss' or '.rodata'.
   */
  if (!bpf_map__is_internal(map))
    return -ENOENT;

  id = btf__find_by_name(obj->btf, map->real_name);
  if (id < 0)
    return id;

  map->btf_key_type_id = 0;
  map->btf_value_type_id = id;
  return 0;
}

static int bpf_get_map_info_from_fdinfo(int fd, struct bpf_map_info *info)
{
  char file[PATH_MAX], buff[4096];
  FILE *fp;
  __u32 val;
  int err;

  snprintf(file, sizeof(file), "/proc/%d/fdinfo/%d", getpid(), fd);
  memset(info, 0, sizeof(*info));

  fp = fopen(file, "re");
  if (!fp) {
    err = -errno;
    pr_warn("failed to open %s: %d. No procfs support?\n", file,
      err);
    return err;
  }

  while (fgets(buff, sizeof(buff), fp)) {
    if (sscanf(buff, "map_type:\t%u", &val) == 1)
      info->type = val;
    else if (sscanf(buff, "key_size:\t%u", &val) == 1)
      info->key_size = val;
    else if (sscanf(buff, "value_size:\t%u", &val) == 1)
      info->value_size = val;
    else if (sscanf(buff, "max_entries:\t%u", &val) == 1)
      info->max_entries = val;
    else if (sscanf(buff, "map_flags:\t%i", &val) == 1)
      info->map_flags = val;
  }

  fclose(fp);

  return 0;
}

bool bpf_map__autocreate(const struct bpf_map *map)
{
  return map->autocreate;
}

int bpf_map__set_autocreate(struct bpf_map *map, bool autocreate)
{
  if (map->obj->loaded)
    return libbpf_err(-EBUSY);

  map->autocreate = autocreate;
  return 0;
}

int bpf_map__reuse_fd(struct bpf_map *map, int fd)
{
  struct bpf_map_info info;
  __u32 len = sizeof(info), name_len;
  int new_fd, err;
  char *new_name;

  memset(&info, 0, len);
  err = bpf_map_get_info_by_fd(fd, &info, &len);
  if (err && errno == EINVAL)
    err = bpf_get_map_info_from_fdinfo(fd, &info);
  if (err)
    return libbpf_err(err);

  name_len = strlen(info.name);
  if (name_len == BPF_OBJ_NAME_LEN - 1 && strncmp(map->name, info.name, name_len) == 0)
    new_name = strdup(map->name);
  else
    new_name = strdup(info.name);

  if (!new_name)
    return libbpf_err(-errno);

  /*
   * Like dup(), but make sure new FD is >= 3 and has O_CLOEXEC set.
   * This is similar to what we do in ensure_good_fd(), but without
   * closing original FD.
   */
  new_fd = fcntl(fd, F_DUPFD_CLOEXEC, 3);
  if (new_fd < 0) {
    err = -errno;
    goto err_free_new_name;
  }

  err = zclose(map->fd);
  if (err) {
    err = -errno;
    goto err_close_new_fd;
  }
  free(map->name);

  map->fd = new_fd;
  map->name = new_name;
  map->def.type = info.type;
  map->def.key_size = info.key_size;
  map->def.value_size = info.value_size;
  map->def.max_entries = info.max_entries;
  map->def.map_flags = info.map_flags;
  map->btf_key_type_id = info.btf_key_type_id;
  map->btf_value_type_id = info.btf_value_type_id;
  map->reused = true;
  map->map_extra = info.map_extra;

  return 0;

err_close_new_fd:
  close(new_fd);
err_free_new_name:
  free(new_name);
  return libbpf_err(err);
}

__u32 bpf_map__max_entries(const struct bpf_map *map)
{
  return map->def.max_entries;
}

struct bpf_map *bpf_map__inner_map(struct bpf_map *map)
{
  if (!bpf_map_type__is_map_in_map(map->def.type))
    return errno = EINVAL, NULL;

  return map->inner_map;
}

int bpf_map__set_max_entries(struct bpf_map *map, __u32 max_entries)
{
  if (map->obj->loaded)
    return libbpf_err(-EBUSY);

  map->def.max_entries = max_entries;

  /* auto-adjust BPF ringbuf map max_entries to be a multiple of page size */
  if (map_is_ringbuf(map))
    map->def.max_entries = adjust_ringbuf_sz(map->def.max_entries);

  return 0;
}

static int
bpf_object__probe_loading(struct bpf_object *obj)
{
  char *cp, errmsg[STRERR_BUFSIZE];
  struct bpf_insn insns[] = {
    BPF_MOV64_IMM(BPF_REG_0, 0),
    BPF_EXIT_INSN(),
  };
  int ret, insn_cnt = ARRAY_SIZE(insns);

  if (obj->gen_loader)
    return 0;

  ret = bump_rlimit_memlock();
  if (ret)
    pr_warn("Failed to bump RLIMIT_MEMLOCK (err = %d), you might need to do it explicitly!\n", ret);

  /* make sure basic loading works */
  ret = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, NULL, "GPL", insns, insn_cnt, NULL);
  if (ret < 0)
    ret = bpf_prog_load(BPF_PROG_TYPE_TRACEPOINT, NULL, "GPL", insns, insn_cnt, NULL);
  if (ret < 0) {
    ret = errno;
    cp = libbpf_strerror_r(ret, errmsg, sizeof(errmsg));
    pr_warn("Error in %s():%s(%d). Couldn't load trivial BPF "
      "program. Make sure your kernel supports BPF "
      "(CONFIG_BPF_SYSCALL=y) and/or that RLIMIT_MEMLOCK is "
      "set to big enough value.\n", __func__, cp, ret);
    return -ret;
  }
  close(ret);

  return 0;
}

static int probe_fd(int fd)
{
  if (fd >= 0)
    close(fd);
  return fd >= 0;
}

static int probe_kern_prog_name(void)
{
  const size_t attr_sz = offsetofend(union bpf_attr, prog_name);
  struct bpf_insn insns[] = {
    BPF_MOV64_IMM(BPF_REG_0, 0),
    BPF_EXIT_INSN(),
  };
  union bpf_attr attr;
  int ret;

  memset(&attr, 0, attr_sz);
  attr.prog_type = BPF_PROG_TYPE_SOCKET_FILTER;
  attr.license = ptr_to_u64("GPL");
  attr.insns = ptr_to_u64(insns);
  attr.insn_cnt = (__u32)ARRAY_SIZE(insns);
  libbpf_strlcpy(attr.prog_name, "libbpf_nametest", sizeof(attr.prog_name));

  /* make sure loading with name works */
  ret = sys_bpf_prog_load(&attr, attr_sz, PROG_LOAD_ATTEMPTS);
  return probe_fd(ret);
}

static int probe_kern_global_data(void)
{
  char *cp, errmsg[STRERR_BUFSIZE];
  struct bpf_insn insns[] = {
    BPF_LD_MAP_VALUE(BPF_REG_1, 0, 16),
    BPF_ST_MEM(BPF_DW, BPF_REG_1, 0, 42),
    BPF_MOV64_IMM(BPF_REG_0, 0),
    BPF_EXIT_INSN(),
  };
  int ret, map, insn_cnt = ARRAY_SIZE(insns);

  map = bpf_map_create(BPF_MAP_TYPE_ARRAY, "libbpf_global", sizeof(int), 32, 1, NULL);
  if (map < 0) {
    ret = -errno;
    cp = libbpf_strerror_r(ret, errmsg, sizeof(errmsg));
    pr_warn("Error in %s():%s(%d). Couldn't create simple array map.\n",
      __func__, cp, -ret);
    return ret;
  }

  insns[0].imm = map;

  ret = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, NULL, "GPL", insns, insn_cnt, NULL);
  close(map);
  return probe_fd(ret);
}

static int probe_kern_btf(void)
{
  static const char strs[] = "\0int";
  __u32 types[] = {
    /* int */
    BTF_TYPE_INT_ENC(1, BTF_INT_SIGNED, 0, 32, 4),
  };

  return probe_fd(libbpf__load_raw_btf((char *)types, sizeof(types),
               strs, sizeof(strs)));
}

static int probe_kern_btf_func(void)
{
  static const char strs[] = "\0int\0x\0a";
  /* void x(int a) {} */
  __u32 types[] = {
    /* int */
    BTF_TYPE_INT_ENC(1, BTF_INT_SIGNED, 0, 32, 4),  /* [1] */
    /* FUNC_PROTO */                                /* [2] */
    BTF_TYPE_ENC(0, BTF_INFO_ENC(BTF_KIND_FUNC_PROTO, 0, 1), 0),
    BTF_PARAM_ENC(7, 1),
    /* FUNC x */                                    /* [3] */
    BTF_TYPE_ENC(5, BTF_INFO_ENC(BTF_KIND_FUNC, 0, 0), 2),
  };

  return probe_fd(libbpf__load_raw_btf((char *)types, sizeof(types),
               strs, sizeof(strs)));
}

static int probe_kern_btf_func_global(void)
{
  static const char strs[] = "\0int\0x\0a";
  /* static void x(int a) {} */
  __u32 types[] = {
    /* int */
    BTF_TYPE_INT_ENC(1, BTF_INT_SIGNED, 0, 32, 4),  /* [1] */
    /* FUNC_PROTO */                                /* [2] */
    BTF_TYPE_ENC(0, BTF_INFO_ENC(BTF_KIND_FUNC_PROTO, 0, 1), 0),
    BTF_PARAM_ENC(7, 1),
    /* FUNC x BTF_FUNC_GLOBAL */                    /* [3] */
    BTF_TYPE_ENC(5, BTF_INFO_ENC(BTF_KIND_FUNC, 0, BTF_FUNC_GLOBAL), 2),
  };

  return probe_fd(libbpf__load_raw_btf((char *)types, sizeof(types),
               strs, sizeof(strs)));
}

static int probe_kern_btf_datasec(void)
{
  static const char strs[] = "\0x\0.data";
  /* static int a; */
  __u32 types[] = {
    /* int */
    BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, 4),  /* [1] */
    /* VAR x */                                     /* [2] */
    BTF_TYPE_ENC(1, BTF_INFO_ENC(BTF_KIND_VAR, 0, 0), 1),
    BTF_VAR_STATIC,
    /* DATASEC val */                               /* [3] */
    BTF_TYPE_ENC(3, BTF_INFO_ENC(BTF_KIND_DATASEC, 0, 1), 4),
    BTF_VAR_SECINFO_ENC(2, 0, 4),
  };

  return probe_fd(libbpf__load_raw_btf((char *)types, sizeof(types),
               strs, sizeof(strs)));
}

static int probe_kern_btf_float(void)
{
  static const char strs[] = "\0float";
  __u32 types[] = {
    /* float */
    BTF_TYPE_FLOAT_ENC(1, 4),
  };

  return probe_fd(libbpf__load_raw_btf((char *)types, sizeof(types),
               strs, sizeof(strs)));
}

static int probe_kern_btf_decl_tag(void)
{
  static const char strs[] = "\0tag";
  __u32 types[] = {
    /* int */
    BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, 4),  /* [1] */
    /* VAR x */                                     /* [2] */
    BTF_TYPE_ENC(1, BTF_INFO_ENC(BTF_KIND_VAR, 0, 0), 1),
    BTF_VAR_STATIC,
    /* attr */
    BTF_TYPE_DECL_TAG_ENC(1, 2, -1),
  };

  return probe_fd(libbpf__load_raw_btf((char *)types, sizeof(types),
               strs, sizeof(strs)));
}

static int probe_kern_btf_type_tag(void)
{
  static const char strs[] = "\0tag";
  __u32 types[] = {
    /* int */
    BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, 4),    /* [1] */
    /* attr */
    BTF_TYPE_TYPE_TAG_ENC(1, 1),       /* [2] */
    /* ptr */
    BTF_TYPE_ENC(0, BTF_INFO_ENC(BTF_KIND_PTR, 0, 0), 2), /* [3] */
  };

  return probe_fd(libbpf__load_raw_btf((char *)types, sizeof(types),
               strs, sizeof(strs)));
}

static int probe_kern_array_mmap(void)
{
  LIBBPF_OPTS(bpf_map_create_opts, opts, .map_flags = BPF_F_MMAPABLE);
  int fd;

  fd = bpf_map_create(BPF_MAP_TYPE_ARRAY, "libbpf_mmap", sizeof(int), sizeof(int), 1, &opts);
  return probe_fd(fd);
}

static int probe_kern_exp_attach_type(void)
{
  LIBBPF_OPTS(bpf_prog_load_opts, opts, .expected_attach_type = BPF_CGROUP_INET_SOCK_CREATE);
  struct bpf_insn insns[] = {
    BPF_MOV64_IMM(BPF_REG_0, 0),
    BPF_EXIT_INSN(),
  };
  int fd, insn_cnt = ARRAY_SIZE(insns);

  /* use any valid combination of program type and (optional)
   * non-zero expected attach type (i.e., not a BPF_CGROUP_INET_INGRESS)
   * to see if kernel supports expected_attach_type field for
   * BPF_PROG_LOAD command
   */
  fd = bpf_prog_load(BPF_PROG_TYPE_CGROUP_SOCK, NULL, "GPL", insns, insn_cnt, &opts);
  return probe_fd(fd);
}

static int probe_kern_probe_read_kernel(void)
{
  struct bpf_insn insns[] = {
    BPF_MOV64_REG(BPF_REG_1, BPF_REG_10),  /* r1 = r10 (fp) */
    BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, -8), /* r1 += -8 */
    BPF_MOV64_IMM(BPF_REG_2, 8),   /* r2 = 8 */
    BPF_MOV64_IMM(BPF_REG_3, 0),   /* r3 = 0 */
    BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_probe_read_kernel),
    BPF_EXIT_INSN(),
  };
  int fd, insn_cnt = ARRAY_SIZE(insns);

  fd = bpf_prog_load(BPF_PROG_TYPE_TRACEPOINT, NULL, "GPL", insns, insn_cnt, NULL);
  return probe_fd(fd);
}

static int probe_prog_bind_map(void)
{
  char *cp, errmsg[STRERR_BUFSIZE];
  struct bpf_insn insns[] = {
    BPF_MOV64_IMM(BPF_REG_0, 0),
    BPF_EXIT_INSN(),
  };
  int ret, map, prog, insn_cnt = ARRAY_SIZE(insns);

  map = bpf_map_create(BPF_MAP_TYPE_ARRAY, "libbpf_det_bind", sizeof(int), 32, 1, NULL);
  if (map < 0) {
    ret = -errno;
    cp = libbpf_strerror_r(ret, errmsg, sizeof(errmsg));
    pr_warn("Error in %s():%s(%d). Couldn't create simple array map.\n",
      __func__, cp, -ret);
    return ret;
  }

  prog = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, NULL, "GPL", insns, insn_cnt, NULL);
  if (prog < 0) {
    close(map);
    return 0;
  }

  ret = bpf_prog_bind_map(prog, map, NULL);

  close(map);
  close(prog);

  return ret >= 0;
}

static int probe_module_btf(void)
{
  static const char strs[] = "\0int";
  __u32 types[] = {
    /* int */
    BTF_TYPE_INT_ENC(1, BTF_INT_SIGNED, 0, 32, 4),
  };
  struct bpf_btf_info info;
  __u32 len = sizeof(info);
  char name[16];
  int fd, err;

  fd = libbpf__load_raw_btf((char *)types, sizeof(types), strs, sizeof(strs));
  if (fd < 0)
    return 0; /* BTF not supported at all */

  memset(&info, 0, sizeof(info));
  info.name = ptr_to_u64(name);
  info.name_len = sizeof(name);

  /* check that BPF_OBJ_GET_INFO_BY_FD supports specifying name pointer;
   * kernel's module BTF support coincides with support for
   * name/name_len fields in struct bpf_btf_info.
   */
  err = bpf_btf_get_info_by_fd(fd, &info, &len);
  close(fd);
  return !err;
}

static int probe_perf_link(void)
{
  struct bpf_insn insns[] = {
    BPF_MOV64_IMM(BPF_REG_0, 0),
    BPF_EXIT_INSN(),
  };
  int prog_fd, link_fd, err;

  prog_fd = bpf_prog_load(BPF_PROG_TYPE_TRACEPOINT, NULL, "GPL",
        insns, ARRAY_SIZE(insns), NULL);
  if (prog_fd < 0)
    return -errno;

  /* use invalid perf_event FD to get EBADF, if link is supported;
   * otherwise EINVAL should be returned
   */
  link_fd = bpf_link_create(prog_fd, -1, BPF_PERF_EVENT, NULL);
  err = -errno; /* close() can clobber errno */

  if (link_fd >= 0)
    close(link_fd);
  close(prog_fd);

  return link_fd < 0 && err == -EBADF;
}

static int probe_uprobe_multi_link(void)
{
  LIBBPF_OPTS(bpf_prog_load_opts, load_opts,
    .expected_attach_type = BPF_TRACE_UPROBE_MULTI,
  );
  LIBBPF_OPTS(bpf_link_create_opts, link_opts);
  struct bpf_insn insns[] = {
    BPF_MOV64_IMM(BPF_REG_0, 0),
    BPF_EXIT_INSN(),
  };
  int prog_fd, link_fd, err;
  unsigned long offset = 0;

  prog_fd = bpf_prog_load(BPF_PROG_TYPE_KPROBE, NULL, "GPL",
        insns, ARRAY_SIZE(insns), &load_opts);
  if (prog_fd < 0)
    return -errno;

  /* Creating uprobe in '/' binary should fail with -EBADF. */
  link_opts.uprobe_multi.path = "/";
  link_opts.uprobe_multi.offsets = &offset;
  link_opts.uprobe_multi.cnt = 1;

  link_fd = bpf_link_create(prog_fd, -1, BPF_TRACE_UPROBE_MULTI, &link_opts);
  err = -errno; /* close() can clobber errno */

  if (link_fd >= 0)
    close(link_fd);
  close(prog_fd);

  return link_fd < 0 && err == -EBADF;
}

static int probe_kern_bpf_cookie(void)
{
  struct bpf_insn insns[] = {
    BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0, BPF_FUNC_get_attach_cookie),
    BPF_EXIT_INSN(),
  };
  int ret, insn_cnt = ARRAY_SIZE(insns);

  ret = bpf_prog_load(BPF_PROG_TYPE_KPROBE, NULL, "GPL", insns, insn_cnt, NULL);
  return probe_fd(ret);
}

static int probe_kern_btf_enum64(void)
{
  static const char strs[] = "\0enum64";
  __u32 types[] = {
    BTF_TYPE_ENC(1, BTF_INFO_ENC(BTF_KIND_ENUM64, 0, 0), 8),
  };

  return probe_fd(libbpf__load_raw_btf((char *)types, sizeof(types),
               strs, sizeof(strs)));
}

static int probe_kern_syscall_wrapper(void);

enum kern_feature_result {
  FEAT_UNKNOWN = 0,
  FEAT_SUPPORTED = 1,
  FEAT_MISSING = 2,
};

typedef int (*feature_probe_fn)(void);

static struct kern_feature_desc {
  const char *desc;
  feature_probe_fn probe;
  enum kern_feature_result res;
} feature_probes[__FEAT_CNT] = {
  [FEAT_PROG_NAME] = {
    "BPF program name", probe_kern_prog_name,
  },
  [FEAT_GLOBAL_DATA] = {
    "global variables", probe_kern_global_data,
  },
  [FEAT_BTF] = {
    "minimal BTF", probe_kern_btf,
  },
  [FEAT_BTF_FUNC] = {
    "BTF functions", probe_kern_btf_func,
  },
  [FEAT_BTF_GLOBAL_FUNC] = {
    "BTF global function", probe_kern_btf_func_global,
  },
  [FEAT_BTF_DATASEC] = {
    "BTF data section and variable", probe_kern_btf_datasec,
  },
  [FEAT_ARRAY_MMAP] = {
    "ARRAY map mmap()", probe_kern_array_mmap,
  },
  [FEAT_EXP_ATTACH_TYPE] = {
    "BPF_PROG_LOAD expected_attach_type attribute",
    probe_kern_exp_attach_type,
  },
  [FEAT_PROBE_READ_KERN] = {
    "bpf_probe_read_kernel() helper", probe_kern_probe_read_kernel,
  },
  [FEAT_PROG_BIND_MAP] = {
    "BPF_PROG_BIND_MAP support", probe_prog_bind_map,
  },
  [FEAT_MODULE_BTF] = {
    "module BTF support", probe_module_btf,
  },
  [FEAT_BTF_FLOAT] = {
    "BTF_KIND_FLOAT support", probe_kern_btf_float,
  },
  [FEAT_PERF_LINK] = {
    "BPF perf link support", probe_perf_link,
  },
  [FEAT_BTF_DECL_TAG] = {
    "BTF_KIND_DECL_TAG support", probe_kern_btf_decl_tag,
  },
  [FEAT_BTF_TYPE_TAG] = {
    "BTF_KIND_TYPE_TAG support", probe_kern_btf_type_tag,
  },
  [FEAT_MEMCG_ACCOUNT] = {
    "memcg-based memory accounting", probe_memcg_account,
  },
  [FEAT_BPF_COOKIE] = {
    "BPF cookie support", probe_kern_bpf_cookie,
  },
  [FEAT_BTF_ENUM64] = {
    "BTF_KIND_ENUM64 support", probe_kern_btf_enum64,
  },
  [FEAT_SYSCALL_WRAPPER] = {
    "Kernel using syscall wrapper", probe_kern_syscall_wrapper,
  },
  [FEAT_UPROBE_MULTI_LINK] = {
    "BPF multi-uprobe link support", probe_uprobe_multi_link,
  },
};

bool kernel_supports(const struct bpf_object *obj, enum kern_feature_id feat_id)
{
  struct kern_feature_desc *feat = &feature_probes[feat_id];
  int ret;

  if (obj && obj->gen_loader)
    /* To generate loader program assume the latest kernel
     * to avoid doing extra prog_load, map_create syscalls.
     */
    return true;

  if (READ_ONCE(feat->res) == FEAT_UNKNOWN) {
    ret = feat->probe();
    if (ret > 0) {
      WRITE_ONCE(feat->res, FEAT_SUPPORTED);
    } else if (ret == 0) {
      WRITE_ONCE(feat->res, FEAT_MISSING);
    } else {
      pr_warn("Detection of kernel %s support failed: %d\n", feat->desc, ret);
      WRITE_ONCE(feat->res, FEAT_MISSING);
    }
  }

  return READ_ONCE(feat->res) == FEAT_SUPPORTED;
}

static bool map_is_reuse_compat(const struct bpf_map *map, int map_fd)
{
  struct bpf_map_info map_info;
  char msg[STRERR_BUFSIZE];
  __u32 map_info_len = sizeof(map_info);
  int err;

  memset(&map_info, 0, map_info_len);
  err = bpf_map_get_info_by_fd(map_fd, &map_info, &map_info_len);
  if (err && errno == EINVAL)
    err = bpf_get_map_info_from_fdinfo(map_fd, &map_info);
  if (err) {
    pr_warn("failed to get map info for map FD %d: %s\n", map_fd,
      libbpf_strerror_r(errno, msg, sizeof(msg)));
    return false;
  }

  return (map_info.type == map->def.type &&
    map_info.key_size == map->def.key_size &&
    map_info.value_size == map->def.value_size &&
    map_info.max_entries == map->def.max_entries &&
    map_info.map_flags == map->def.map_flags &&
    map_info.map_extra == map->map_extra);
}

static int
bpf_object__reuse_map(struct bpf_map *map)
{
  char *cp, errmsg[STRERR_BUFSIZE];
  int err, pin_fd;

  pin_fd = bpf_obj_get(map->pin_path);
  if (pin_fd < 0) {
    err = -errno;
    if (err == -ENOENT) {
      pr_debug("found no pinned map to reuse at '%s'\n",
         map->pin_path);
      return 0;
    }

    cp = libbpf_strerror_r(-err, errmsg, sizeof(errmsg));
    pr_warn("couldn't retrieve pinned map '%s': %s\n",
      map->pin_path, cp);
    return err;
  }

  if (!map_is_reuse_compat(map, pin_fd)) {
    pr_warn("couldn't reuse pinned map at '%s': parameter mismatch\n",
      map->pin_path);
    close(pin_fd);
    return -EINVAL;
  }

  err = bpf_map__reuse_fd(map, pin_fd);
  close(pin_fd);
  if (err)
    return err;

  map->pinned = true;
  pr_debug("reused pinned map at '%s'\n", map->pin_path);

  return 0;
}

static int
bpf_object__populate_internal_map(struct bpf_object *obj, struct bpf_map *map)
{
  enum libbpf_map_type map_type = map->libbpf_type;
  char *cp, errmsg[STRERR_BUFSIZE];
  int err, zero = 0;

  if (obj->gen_loader) {
    bpf_gen__map_update_elem(obj->gen_loader, map - obj->maps,
           map->mmaped, map->def.value_size);
    if (map_type == LIBBPF_MAP_RODATA || map_type == LIBBPF_MAP_KCONFIG)
      bpf_gen__map_freeze(obj->gen_loader, map - obj->maps);
    return 0;
  }
  err = bpf_map_update_elem(map->fd, &zero, map->mmaped, 0);
  if (err) {
    err = -errno;
    cp = libbpf_strerror_r(err, errmsg, sizeof(errmsg));
    pr_warn("Error setting initial map(%s) contents: %s\n",
      map->name, cp);
    return err;
  }

  /* Freeze .rodata and .kconfig map as read-only from syscall side. */
  if (map_type == LIBBPF_MAP_RODATA || map_type == LIBBPF_MAP_KCONFIG) {
    err = bpf_map_freeze(map->fd);
    if (err) {
      err = -errno;
      cp = libbpf_strerror_r(err, errmsg, sizeof(errmsg));
      pr_warn("Error freezing map(%s) as read-only: %s\n",
        map->name, cp);
      return err;
    }
  }
  return 0;
}

static void bpf_map__destroy(struct bpf_map *map);

static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map, bool is_inner)
{
  LIBBPF_OPTS(bpf_map_create_opts, create_attr);
  struct bpf_map_def *def = &map->def;
  const char *map_name = NULL;
  int err = 0;

  if (kernel_supports(obj, FEAT_PROG_NAME))
    map_name = map->name;
  create_attr.map_ifindex = map->map_ifindex;
  create_attr.map_flags = def->map_flags;
  create_attr.numa_node = map->numa_node;
  create_attr.map_extra = map->map_extra;

  if (bpf_map__is_struct_ops(map))
    create_attr.btf_vmlinux_value_type_id = map->btf_vmlinux_value_type_id;

  if (obj->btf && btf__fd(obj->btf) >= 0) {
    create_attr.btf_fd = btf__fd(obj->btf);
    create_attr.btf_key_type_id = map->btf_key_type_id;
    create_attr.btf_value_type_id = map->btf_value_type_id;
  }

  if (bpf_map_type__is_map_in_map(def->type)) {
    if (map->inner_map) {
      err = bpf_object__create_map(obj, map->inner_map, true);
      if (err) {
        pr_warn("map '%s': failed to create inner map: %d\n",
          map->name, err);
        return err;
      }
      map->inner_map_fd = bpf_map__fd(map->inner_map);
    }
    if (map->inner_map_fd >= 0)
      create_attr.inner_map_fd = map->inner_map_fd;
  }

  switch (def->type) {
  case BPF_MAP_TYPE_PERF_EVENT_ARRAY:
  case BPF_MAP_TYPE_CGROUP_ARRAY:
  case BPF_MAP_TYPE_STACK_TRACE:
  case BPF_MAP_TYPE_ARRAY_OF_MAPS:
  case BPF_MAP_TYPE_HASH_OF_MAPS:
  case BPF_MAP_TYPE_DEVMAP:
  case BPF_MAP_TYPE_DEVMAP_HASH:
  case BPF_MAP_TYPE_CPUMAP:
  case BPF_MAP_TYPE_XSKMAP:
  case BPF_MAP_TYPE_SOCKMAP:
  case BPF_MAP_TYPE_SOCKHASH:
  case BPF_MAP_TYPE_QUEUE:
  case BPF_MAP_TYPE_STACK:
    create_attr.btf_fd = 0;
    create_attr.btf_key_type_id = 0;
    create_attr.btf_value_type_id = 0;
    map->btf_key_type_id = 0;
    map->btf_value_type_id = 0;
  default:
    break;
  }

  if (obj->gen_loader) {
    bpf_gen__map_create(obj->gen_loader, def->type, map_name,
            def->key_size, def->value_size, def->max_entries,
            &create_attr, is_inner ? -1 : map - obj->maps);
    /* Pretend to have valid FD to pass various fd >= 0 checks.
     * This fd == 0 will not be used with any syscall and will be reset to -1 eventually.
     */
    map->fd = 0;
  } else {
    map->fd = bpf_map_create(def->type, map_name,
           def->key_size, def->value_size,
           def->max_entries, &create_attr);
  }
  if (map->fd < 0 && (create_attr.btf_key_type_id ||
          create_attr.btf_value_type_id)) {
    char *cp, errmsg[STRERR_BUFSIZE];

    err = -errno;
    cp = libbpf_strerror_r(err, errmsg, sizeof(errmsg));
    pr_warn("Error in bpf_create_map_xattr(%s):%s(%d). Retrying without BTF.\n",
      map->name, cp, err);
    create_attr.btf_fd = 0;
    create_attr.btf_key_type_id = 0;
    create_attr.btf_value_type_id = 0;
    map->btf_key_type_id = 0;
    map->btf_value_type_id = 0;
    map->fd = bpf_map_create(def->type, map_name,
           def->key_size, def->value_size,
           def->max_entries, &create_attr);
  }

  err = map->fd < 0 ? -errno : 0;

  if (bpf_map_type__is_map_in_map(def->type) && map->inner_map) {
    if (obj->gen_loader)
      map->inner_map->fd = -1;
    bpf_map__destroy(map->inner_map);
    zfree(&map->inner_map);
  }

  return err;
}

static int init_map_in_map_slots(struct bpf_object *obj, struct bpf_map *map)
{
  const struct bpf_map *targ_map;
  unsigned int i;
  int fd, err = 0;

  for (i = 0; i < map->init_slots_sz; i++) {
    if (!map->init_slots[i])
      continue;

    targ_map = map->init_slots[i];
    fd = bpf_map__fd(targ_map);

    if (obj->gen_loader) {
      bpf_gen__populate_outer_map(obj->gen_loader,
                map - obj->maps, i,
                targ_map - obj->maps);
    } else {
      err = bpf_map_update_elem(map->fd, &i, &fd, 0);
    }
    if (err) {
      err = -errno;
      pr_warn("map '%s': failed to initialize slot [%d] to map '%s' fd=%d: %d\n",
        map->name, i, targ_map->name, fd, err);
      return err;
    }
    pr_debug("map '%s': slot [%d] set to map '%s' fd=%d\n",
       map->name, i, targ_map->name, fd);
  }

  zfree(&map->init_slots);
  map->init_slots_sz = 0;

  return 0;
}

static int init_prog_array_slots(struct bpf_object *obj, struct bpf_map *map)
{
  const struct bpf_program *targ_prog;
  unsigned int i;
  int fd, err;

  if (obj->gen_loader)
    return -ENOTSUP;

  for (i = 0; i < map->init_slots_sz; i++) {
    if (!map->init_slots[i])
      continue;

    targ_prog = map->init_slots[i];
    fd = bpf_program__fd(targ_prog);

    err = bpf_map_update_elem(map->fd, &i, &fd, 0);
    if (err) {
      err = -errno;
      pr_warn("map '%s': failed to initialize slot [%d] to prog '%s' fd=%d: %d\n",
        map->name, i, targ_prog->name, fd, err);
      return err;
    }
    pr_debug("map '%s': slot [%d] set to prog '%s' fd=%d\n",
       map->name, i, targ_prog->name, fd);
  }

  zfree(&map->init_slots);
  map->init_slots_sz = 0;

  return 0;
}

static int bpf_object_init_prog_arrays(struct bpf_object *obj)
{
  struct bpf_map *map;
  int i, err;

  for (i = 0; i < obj->nr_maps; i++) {
    map = &obj->maps[i];

    if (!map->init_slots_sz || map->def.type != BPF_MAP_TYPE_PROG_ARRAY)
      continue;

    err = init_prog_array_slots(obj, map);
    if (err < 0) {
      zclose(map->fd);
      return err;
    }
  }
  return 0;
}

static int map_set_def_max_entries(struct bpf_map *map)
{
  if (map->def.type == BPF_MAP_TYPE_PERF_EVENT_ARRAY && !map->def.max_entries) {
    int nr_cpus;

    nr_cpus = libbpf_num_possible_cpus();
    if (nr_cpus < 0) {
      pr_warn("map '%s': failed to determine number of system CPUs: %d\n",
        map->name, nr_cpus);
      return nr_cpus;
    }
    pr_debug("map '%s': setting size to %d\n", map->name, nr_cpus);
    map->def.max_entries = nr_cpus;
  }

  return 0;
}

static int
bpf_object__create_maps(struct bpf_object *obj)
{
  struct bpf_map *map;
  char *cp, errmsg[STRERR_BUFSIZE];
  unsigned int i, j;
  int err;
  bool retried;

  for (i = 0; i < obj->nr_maps; i++) {
    map = &obj->maps[i];

    /* To support old kernels, we skip creating global data maps
     * (.rodata, .data, .kconfig, etc); later on, during program
     * loading, if we detect that at least one of the to-be-loaded
     * programs is referencing any global data map, we'll error
     * out with program name and relocation index logged.
     * This approach allows to accommodate Clang emitting
     * unnecessary .rodata.str1.1 sections for string literals,
     * but also it allows to have CO-RE applications that use
     * global variables in some of BPF programs, but not others.
     * If those global variable-using programs are not loaded at
     * runtime due to bpf_program__set_autoload(prog, false),
     * bpf_object loading will succeed just fine even on old
     * kernels.
     */
    if (bpf_map__is_internal(map) && !kernel_supports(obj, FEAT_GLOBAL_DATA))
      map->autocreate = false;

    if (!map->autocreate) {
      pr_debug("map '%s': skipped auto-creating...\n", map->name);
      continue;
    }

    err = map_set_def_max_entries(map);
    if (err)
      goto err_out;

    retried = false;
retry:
    if (map->pin_path) {
      err = bpf_object__reuse_map(map);
      if (err) {
        pr_warn("map '%s': error reusing pinned map\n",
          map->name);
        goto err_out;
      }
      if (retried && map->fd < 0) {
        pr_warn("map '%s': cannot find pinned map\n",
          map->name);
        err = -ENOENT;
        goto err_out;
      }
    }

    if (map->fd >= 0) {
      pr_debug("map '%s': skipping creation (preset fd=%d)\n",
         map->name, map->fd);
    } else {
      err = bpf_object__create_map(obj, map, false);
      if (err)
        goto err_out;

      pr_debug("map '%s': created successfully, fd=%d\n",
         map->name, map->fd);

      if (bpf_map__is_internal(map)) {
        err = bpf_object__populate_internal_map(obj, map);
        if (err < 0) {
          zclose(map->fd);
          goto err_out;
        }
      }

      if (map->init_slots_sz && map->def.type != BPF_MAP_TYPE_PROG_ARRAY) {
        err = init_map_in_map_slots(obj, map);
        if (err < 0) {
          zclose(map->fd);
          goto err_out;
        }
      }
    }

    if (map->pin_path && !map->pinned) {
      err = bpf_map__pin(map, NULL);
      if (err) {
        zclose(map->fd);
        if (!retried && err == -EEXIST) {
          retried = true;
          goto retry;
        }
        pr_warn("map '%s': failed to auto-pin at '%s': %d\n",
          map->name, map->pin_path, err);
        goto err_out;
      }
    }
  }

  return 0;

err_out:
  cp = libbpf_strerror_r(err, errmsg, sizeof(errmsg));
  pr_warn("map '%s': failed to create: %s(%d)\n", map->name, cp, err);
  pr_perm_msg(err);
  for (j = 0; j < i; j++)
    zclose(obj->maps[j].fd);
  return err;
}

static bool bpf_core_is_flavor_sep(const char *s)
{
  /* check X___Y name pattern, where X and Y are not underscores */
  return s[0] != '_' &&             /* X */
         s[1] == '_' && s[2] == '_' && s[3] == '_' &&   /* ___ */
         s[4] != '_';             /* Y */
}

/* Given 'some_struct_name___with_flavor' return the length of a name prefix
 * before last triple underscore. Struct name part after last triple
 * underscore is ignored by BPF CO-RE relocation during relocation matching.
 */
size_t bpf_core_essential_name_len(const char *name)
{
  size_t n = strlen(name);
  int i;

  for (i = n - 5; i >= 0; i--) {
    if (bpf_core_is_flavor_sep(name + i))
      return i + 1;
  }
  return n;
}

void bpf_core_free_cands(struct bpf_core_cand_list *cands)
{
  if (!cands)
    return;

  free(cands->cands);
  free(cands);
}

int bpf_core_add_cands(struct bpf_core_cand *local_cand,
           size_t local_essent_len,
           const struct btf *targ_btf,
           const char *targ_btf_name,
           int targ_start_id,
           struct bpf_core_cand_list *cands)
{
  struct bpf_core_cand *new_cands, *cand;
  const struct btf_type *t, *local_t;
  const char *targ_name, *local_name;
  size_t targ_essent_len;
  int n, i;

  local_t = btf__type_by_id(local_cand->btf, local_cand->id);
  local_name = btf__str_by_offset(local_cand->btf, local_t->name_off);

  n = btf__type_cnt(targ_btf);
  for (i = targ_start_id; i < n; i++) {
    t = btf__type_by_id(targ_btf, i);
    if (!btf_kind_core_compat(t, local_t))
      continue;

    targ_name = btf__name_by_offset(targ_btf, t->name_off);
    if (str_is_empty(targ_name))
      continue;

    targ_essent_len = bpf_core_essential_name_len(targ_name);
    if (targ_essent_len != local_essent_len)
      continue;

    if (strncmp(local_name, targ_name, local_essent_len) != 0)
      continue;

    pr_debug("CO-RE relocating [%d] %s %s: found target candidate [%d] %s %s in [%s]\n",
       local_cand->id, btf_kind_str(local_t),
       local_name, i, btf_kind_str(t), targ_name,
       targ_btf_name);
    new_cands = libbpf_reallocarray(cands->cands, cands->len + 1,
                sizeof(*cands->cands));
    if (!new_cands)
      return -ENOMEM;

    cand = &new_cands[cands->len];
    cand->btf = targ_btf;
    cand->id = i;

    cands->cands = new_cands;
    cands->len++;
  }
  return 0;
}

static int load_module_btfs(struct bpf_object *obj)
{
  struct bpf_btf_info info;
  struct module_btf *mod_btf;
  struct btf *btf;
  char name[64];
  __u32 id = 0, len;
  int err, fd;

  if (obj->btf_modules_loaded)
    return 0;

  if (obj->gen_loader)
    return 0;

  /* don't do this again, even if we find no module BTFs */
  obj->btf_modules_loaded = true;

  /* kernel too old to support module BTFs */
  if (!kernel_supports(obj, FEAT_MODULE_BTF))
    return 0;

  while (true) {
    err = bpf_btf_get_next_id(id, &id);
    if (err && errno == ENOENT)
      return 0;
    if (err && errno == EPERM) {
      pr_debug("skipping module BTFs loading, missing privileges\n");
      return 0;
    }
    if (err) {
      err = -errno;
      pr_warn("failed to iterate BTF objects: %d\n", err);
      return err;
    }

    fd = bpf_btf_get_fd_by_id(id);
    if (fd < 0) {
      if (errno == ENOENT)
        continue; /* expected race: BTF was unloaded */
      err = -errno;
      pr_warn("failed to get BTF object #%d FD: %d\n", id, err);
      return err;
    }

    len = sizeof(info);
    memset(&info, 0, sizeof(info));
    info.name = ptr_to_u64(name);
    info.name_len = sizeof(name);

    err = bpf_btf_get_info_by_fd(fd, &info, &len);
    if (err) {
      err = -errno;
      pr_warn("failed to get BTF object #%d info: %d\n", id, err);
      goto err_out;
    }

    /* ignore non-module BTFs */
    if (!info.kernel_btf || strcmp(name, "vmlinux") == 0) {
      close(fd);
      continue;
    }

    btf = btf_get_from_fd(fd, obj->btf_vmlinux);
    err = libbpf_get_error(btf);
    if (err) {
      pr_warn("failed to load module [%s]'s BTF object #%d: %d\n",
        name, id, err);
      goto err_out;
    }

    err = libbpf_ensure_mem((void **)&obj->btf_modules, &obj->btf_module_cap,
          sizeof(*obj->btf_modules), obj->btf_module_cnt + 1);
    if (err)
      goto err_out;

    mod_btf = &obj->btf_modules[obj->btf_module_cnt++];

    mod_btf->btf = btf;
    mod_btf->id = id;
    mod_btf->fd = fd;
    mod_btf->name = strdup(name);
    if (!mod_btf->name) {
      err = -ENOMEM;
      goto err_out;
    }
    continue;

err_out:
    close(fd);
    return err;
  }

  return 0;
}

static struct bpf_core_cand_list *
bpf_core_find_cands(struct bpf_object *obj, const struct btf *local_btf, __u32 local_type_id)
{
  struct bpf_core_cand local_cand = {};
  struct bpf_core_cand_list *cands;
  const struct btf *main_btf;
  const struct btf_type *local_t;
  const char *local_name;
  size_t local_essent_len;
  int err, i;

  local_cand.btf = local_btf;
  local_cand.id = local_type_id;
  local_t = btf__type_by_id(local_btf, local_type_id);
  if (!local_t)
    return ERR_PTR(-EINVAL);

  local_name = btf__name_by_offset(local_btf, local_t->name_off);
  if (str_is_empty(local_name))
    return ERR_PTR(-EINVAL);
  local_essent_len = bpf_core_essential_name_len(local_name);

  cands = calloc(1, sizeof(*cands));
  if (!cands)
    return ERR_PTR(-ENOMEM);

  /* Attempt to find target candidates in vmlinux BTF first */
  main_btf = obj->btf_vmlinux_override ?: obj->btf_vmlinux;
  err = bpf_core_add_cands(&local_cand, local_essent_len, main_btf, "vmlinux", 1, cands);
  if (err)
    goto err_out;

  /* if vmlinux BTF has any candidate, don't got for module BTFs */
  if (cands->len)
    return cands;

  /* if vmlinux BTF was overridden, don't attempt to load module BTFs */
  if (obj->btf_vmlinux_override)
    return cands;

  /* now look through module BTFs, trying to still find candidates */
  err = load_module_btfs(obj);
  if (err)
    goto err_out;

  for (i = 0; i < obj->btf_module_cnt; i++) {
    err = bpf_core_add_cands(&local_cand, local_essent_len,
           obj->btf_modules[i].btf,
           obj->btf_modules[i].name,
           btf__type_cnt(obj->btf_vmlinux),
           cands);
    if (err)
      goto err_out;
  }

  return cands;
err_out:
  bpf_core_free_cands(cands);
  return ERR_PTR(err);
}

/* Check local and target types for compatibility. This check is used for
 * type-based CO-RE relocations and follow slightly different rules than
 * field-based relocations. This function assumes that root types were already
 * checked for name match. Beyond that initial root-level name check, names
 * are completely ignored. Compatibility rules are as follows:
 *   - any two STRUCTs/UNIONs/FWDs/ENUMs/INTs are considered compatible, but
 *     kind should match for local and target types (i.e., STRUCT is not
 *     compatible with UNION);
 *   - for ENUMs, the size is ignored;
 *   - for INT, size and signedness are ignored;
 *   - for ARRAY, dimensionality is ignored, element types are checked for
 *     compatibility recursively;
 *   - CONST/VOLATILE/RESTRICT modifiers are ignored;
 *   - TYPEDEFs/PTRs are compatible if types they pointing to are compatible;
 *   - FUNC_PROTOs are compatible if they have compatible signature: same
 *     number of input args and compatible return and argument types.
 * These rules are not set in stone and probably will be adjusted as we get
 * more experience with using BPF CO-RE relocations.
 */
int bpf_core_types_are_compat(const struct btf *local_btf, __u32 local_id,
            const struct btf *targ_btf, __u32 targ_id)
{
  return __bpf_core_types_are_compat(local_btf, local_id, targ_btf, targ_id, 32);
}

int bpf_core_types_match(const struct btf *local_btf, __u32 local_id,
       const struct btf *targ_btf, __u32 targ_id)
{
  return __bpf_core_types_match(local_btf, local_id, targ_btf, targ_id, false, 32);
}

static size_t bpf_core_hash_fn(const long key, void *ctx)
{
  return key;
}

static bool bpf_core_equal_fn(const long k1, const long k2, void *ctx)
{
  return k1 == k2;
}

static int record_relo_core(struct bpf_program *prog,
          const struct bpf_core_relo *core_relo, int insn_idx)
{
  struct reloc_desc *relos, *relo;

  relos = libbpf_reallocarray(prog->reloc_desc,
            prog->nr_reloc + 1, sizeof(*relos));
  if (!relos)
    return -ENOMEM;
  relo = &relos[prog->nr_reloc];
  relo->type = RELO_CORE;
  relo->insn_idx = insn_idx;
  relo->core_relo = core_relo;
  prog->reloc_desc = relos;
  prog->nr_reloc++;
  return 0;
}

static const struct bpf_core_relo *find_relo_core(struct bpf_program *prog, int insn_idx)
{
  struct reloc_desc *relo;
  int i;

  for (i = 0; i < prog->nr_reloc; i++) {
    relo = &prog->reloc_desc[i];
    if (relo->type != RELO_CORE || relo->insn_idx != insn_idx)
      continue;

    return relo->core_relo;
  }

  return NULL;
}

static int bpf_core_resolve_relo(struct bpf_program *prog,
         const struct bpf_core_relo *relo,
         int relo_idx,
         const struct btf *local_btf,
         struct hashmap *cand_cache,
         struct bpf_core_relo_res *targ_res)
{
  struct bpf_core_spec specs_scratch[3] = {};
  struct bpf_core_cand_list *cands = NULL;
  const char *prog_name = prog->name;
  const struct btf_type *local_type;
  const char *local_name;
  __u32 local_id = relo->type_id;
  int err;

  local_type = btf__type_by_id(local_btf, local_id);
  if (!local_type)
    return -EINVAL;

  local_name = btf__name_by_offset(local_btf, local_type->name_off);
  if (!local_name)
    return -EINVAL;

  if (relo->kind != BPF_CORE_TYPE_ID_LOCAL &&
      !hashmap__find(cand_cache, local_id, &cands)) {
    cands = bpf_core_find_cands(prog->obj, local_btf, local_id);
    if (IS_ERR(cands)) {
      pr_warn("prog '%s': relo #%d: target candidate search failed for [%d] %s %s: %ld\n",
        prog_name, relo_idx, local_id, btf_kind_str(local_type),
        local_name, PTR_ERR(cands));
      return PTR_ERR(cands);
    }
    err = hashmap__set(cand_cache, local_id, cands, NULL, NULL);
    if (err) {
      bpf_core_free_cands(cands);
      return err;
    }
  }

  return bpf_core_calc_relo_insn(prog_name, relo, relo_idx, local_btf, cands, specs_scratch,
               targ_res);
}

static int
bpf_object__relocate_core(struct bpf_object *obj, const char *targ_btf_path)
{
  const struct btf_ext_info_sec *sec;
  struct bpf_core_relo_res targ_res;
  const struct bpf_core_relo *rec;
  const struct btf_ext_info *seg;
  struct hashmap_entry *entry;
  struct hashmap *cand_cache = NULL;
  struct bpf_program *prog;
  struct bpf_insn *insn;
  const char *sec_name;
  int i, err = 0, insn_idx, sec_idx, sec_num;

  if (obj->btf_ext->core_relo_info.len == 0)
    return 0;

  if (targ_btf_path) {
    obj->btf_vmlinux_override = btf__parse(targ_btf_path, NULL);
    err = libbpf_get_error(obj->btf_vmlinux_override);
    if (err) {
      pr_warn("failed to parse target BTF: %d\n", err);
      return err;
    }
  }

  cand_cache = hashmap__new(bpf_core_hash_fn, bpf_core_equal_fn, NULL);
  if (IS_ERR(cand_cache)) {
    err = PTR_ERR(cand_cache);
    goto out;
  }

  seg = &obj->btf_ext->core_relo_info;
  sec_num = 0;
  for_each_btf_ext_sec(seg, sec) {
    sec_idx = seg->sec_idxs[sec_num];
    sec_num++;

    sec_name = btf__name_by_offset(obj->btf, sec->sec_name_off);
    if (str_is_empty(sec_name)) {
      err = -EINVAL;
      goto out;
    }

    pr_debug("sec '%s': found %d CO-RE relocations\n", sec_name, sec->num_info);

    for_each_btf_ext_rec(seg, sec, i, rec) {
      if (rec->insn_off % BPF_INSN_SZ)
        return -EINVAL;
      insn_idx = rec->insn_off / BPF_INSN_SZ;
      prog = find_prog_by_sec_insn(obj, sec_idx, insn_idx);
      if (!prog) {
        /* When __weak subprog is "overridden" by another instance
         * of the subprog from a different object file, linker still
         * appends all the .BTF.ext info that used to belong to that
         * eliminated subprogram.
         * This is similar to what x86-64 linker does for relocations.
         * So just ignore such relocations just like we ignore
         * subprog instructions when discovering subprograms.
         */
        pr_debug("sec '%s': skipping CO-RE relocation #%d for insn #%d belonging to eliminated weak subprogram\n",
           sec_name, i, insn_idx);
        continue;
      }
      /* no need to apply CO-RE relocation if the program is
       * not going to be loaded
       */
      if (!prog->autoload)
        continue;

      /* adjust insn_idx from section frame of reference to the local
       * program's frame of reference; (sub-)program code is not yet
       * relocated, so it's enough to just subtract in-section offset
       */
      insn_idx = insn_idx - prog->sec_insn_off;
      if (insn_idx >= prog->insns_cnt)
        return -EINVAL;
      insn = &prog->insns[insn_idx];

      err = record_relo_core(prog, rec, insn_idx);
      if (err) {
        pr_warn("prog '%s': relo #%d: failed to record relocation: %d\n",
          prog->name, i, err);
        goto out;
      }

      if (prog->obj->gen_loader)
        continue;

      err = bpf_core_resolve_relo(prog, rec, i, obj->btf, cand_cache, &targ_res);
      if (err) {
        pr_warn("prog '%s': relo #%d: failed to relocate: %d\n",
          prog->name, i, err);
        goto out;
      }

      err = bpf_core_patch_insn(prog->name, insn, insn_idx, rec, i, &targ_res);
      if (err) {
        pr_warn("prog '%s': relo #%d: failed to patch insn #%u: %d\n",
          prog->name, i, insn_idx, err);
        goto out;
      }
    }
  }

out:
  /* obj->btf_vmlinux and module BTFs are freed after object load */
  btf__free(obj->btf_vmlinux_override);
  obj->btf_vmlinux_override = NULL;

  if (!IS_ERR_OR_NULL(cand_cache)) {
    hashmap__for_each_entry(cand_cache, entry, i) {
      bpf_core_free_cands(entry->pvalue);
    }
    hashmap__free(cand_cache);
  }
  return err;
}

/* base map load ldimm64 special constant, used also for log fixup logic */
#define POISON_LDIMM64_MAP_BASE 2001000000
#define POISON_LDIMM64_MAP_PFX "200100"

static void poison_map_ldimm64(struct bpf_program *prog, int relo_idx,
             int insn_idx, struct bpf_insn *insn,
             int map_idx, const struct bpf_map *map)
{
  int i;

  pr_debug("prog '%s': relo #%d: poisoning insn #%d that loads map #%d '%s'\n",
     prog->name, relo_idx, insn_idx, map_idx, map->name);

  /* we turn single ldimm64 into two identical invalid calls */
  for (i = 0; i < 2; i++) {
    insn->code = BPF_JMP | BPF_CALL;
    insn->dst_reg = 0;
    insn->src_reg = 0;
    insn->off = 0;
    /* if this instruction is reachable (not a dead code),
     * verifier will complain with something like:
     * invalid func unknown#2001000123
     * where lower 123 is map index into obj->maps[] array
     */
    insn->imm = POISON_LDIMM64_MAP_BASE + map_idx;

    insn++;
  }
}

/* unresolved kfunc call special constant, used also for log fixup logic */
#define POISON_CALL_KFUNC_BASE 2002000000
#define POISON_CALL_KFUNC_PFX "2002"

static void poison_kfunc_call(struct bpf_program *prog, int relo_idx,
            int insn_idx, struct bpf_insn *insn,
            int ext_idx, const struct extern_desc *ext)
{
  pr_debug("prog '%s': relo #%d: poisoning insn #%d that calls kfunc '%s'\n",
     prog->name, relo_idx, insn_idx, ext->name);

  /* we turn kfunc call into invalid helper call with identifiable constant */
  insn->code = BPF_JMP | BPF_CALL;
  insn->dst_reg = 0;
  insn->src_reg = 0;
  insn->off = 0;
  /* if this instruction is reachable (not a dead code),
   * verifier will complain with something like:
   * invalid func unknown#2001000123
   * where lower 123 is extern index into obj->externs[] array
   */
  insn->imm = POISON_CALL_KFUNC_BASE + ext_idx;
}

/* Relocate data references within program code:
 *  - map references;
 *  - global variable references;
 *  - extern references.
 */
static int
bpf_object__relocate_data(struct bpf_object *obj, struct bpf_program *prog)
{
  int i;

  for (i = 0; i < prog->nr_reloc; i++) {
    struct reloc_desc *relo = &prog->reloc_desc[i];
    struct bpf_insn *insn = &prog->insns[relo->insn_idx];
    const struct bpf_map *map;
    struct extern_desc *ext;

    switch (relo->type) {
    case RELO_LD64:
      map = &obj->maps[relo->map_idx];
      if (obj->gen_loader) {
        insn[0].src_reg = BPF_PSEUDO_MAP_IDX;
        insn[0].imm = relo->map_idx;
      } else if (map->autocreate) {
        insn[0].src_reg = BPF_PSEUDO_MAP_FD;
        insn[0].imm = map->fd;
      } else {
        poison_map_ldimm64(prog, i, relo->insn_idx, insn,
               relo->map_idx, map);
      }
      break;
    case RELO_DATA:
      map = &obj->maps[relo->map_idx];
      insn[1].imm = insn[0].imm + relo->sym_off;
      if (obj->gen_loader) {
        insn[0].src_reg = BPF_PSEUDO_MAP_IDX_VALUE;
        insn[0].imm = relo->map_idx;
      } else if (map->autocreate) {
        insn[0].src_reg = BPF_PSEUDO_MAP_VALUE;
        insn[0].imm = map->fd;
      } else {
        poison_map_ldimm64(prog, i, relo->insn_idx, insn,
               relo->map_idx, map);
      }
      break;
    case RELO_EXTERN_LD64:
      ext = &obj->externs[relo->ext_idx];
      if (ext->type == EXT_KCFG) {
        if (obj->gen_loader) {
          insn[0].src_reg = BPF_PSEUDO_MAP_IDX_VALUE;
          insn[0].imm = obj->kconfig_map_idx;
        } else {
          insn[0].src_reg = BPF_PSEUDO_MAP_VALUE;
          insn[0].imm = obj->maps[obj->kconfig_map_idx].fd;
        }
        insn[1].imm = ext->kcfg.data_off;
      } else /* EXT_KSYM */ {
        if (ext->ksym.type_id && ext->is_set) { /* typed ksyms */
          insn[0].src_reg = BPF_PSEUDO_BTF_ID;
          insn[0].imm = ext->ksym.kernel_btf_id;
          insn[1].imm = ext->ksym.kernel_btf_obj_fd;
        } else { /* typeless ksyms or unresolved typed ksyms */
          insn[0].imm = (__u32)ext->ksym.addr;
          insn[1].imm = ext->ksym.addr >> 32;
        }
      }
      break;
    case RELO_EXTERN_CALL:
      ext = &obj->externs[relo->ext_idx];
      insn[0].src_reg = BPF_PSEUDO_KFUNC_CALL;
      if (ext->is_set) {
        insn[0].imm = ext->ksym.kernel_btf_id;
        insn[0].off = ext->ksym.btf_fd_idx;
      } else { /* unresolved weak kfunc call */
        poison_kfunc_call(prog, i, relo->insn_idx, insn,
              relo->ext_idx, ext);
      }
      break;
    case RELO_SUBPROG_ADDR:
      if (insn[0].src_reg != BPF_PSEUDO_FUNC) {
        pr_warn("prog '%s': relo #%d: bad insn\n",
          prog->name, i);
        return -EINVAL;
      }
      /* handled already */
      break;
    case RELO_CALL:
      /* handled already */
      break;
    case RELO_CORE:
      /* will be handled by bpf_program_record_relos() */
      break;
    default:
      pr_warn("prog '%s': relo #%d: bad relo type %d\n",
        prog->name, i, relo->type);
      return -EINVAL;
    }
  }

  return 0;
}

static int adjust_prog_btf_ext_info(const struct bpf_object *obj,
            const struct bpf_program *prog,
            const struct btf_ext_info *ext_info,
            void **prog_info, __u32 *prog_rec_cnt,
            __u32 *prog_rec_sz)
{
  void *copy_start = NULL, *copy_end = NULL;
  void *rec, *rec_end, *new_prog_info;
  const struct btf_ext_info_sec *sec;
  size_t old_sz, new_sz;
  int i, sec_num, sec_idx, off_adj;

  sec_num = 0;
  for_each_btf_ext_sec(ext_info, sec) {
    sec_idx = ext_info->sec_idxs[sec_num];
    sec_num++;
    if (prog->sec_idx != sec_idx)
      continue;

    for_each_btf_ext_rec(ext_info, sec, i, rec) {
      __u32 insn_off = *(__u32 *)rec / BPF_INSN_SZ;

      if (insn_off < prog->sec_insn_off)
        continue;
      if (insn_off >= prog->sec_insn_off + prog->sec_insn_cnt)
        break;

      if (!copy_start)
        copy_start = rec;
      copy_end = rec + ext_info->rec_size;
    }

    if (!copy_start)
      return -ENOENT;

    /* append func/line info of a given (sub-)program to the main
     * program func/line info
     */
    old_sz = (size_t)(*prog_rec_cnt) * ext_info->rec_size;
    new_sz = old_sz + (copy_end - copy_start);
    new_prog_info = realloc(*prog_info, new_sz);
    if (!new_prog_info)
      return -ENOMEM;
    *prog_info = new_prog_info;
    *prog_rec_cnt = new_sz / ext_info->rec_size;
    memcpy(new_prog_info + old_sz, copy_start, copy_end - copy_start);

    /* Kernel instruction offsets are in units of 8-byte
     * instructions, while .BTF.ext instruction offsets generated
     * by Clang are in units of bytes. So convert Clang offsets
     * into kernel offsets and adjust offset according to program
     * relocated position.
     */
    off_adj = prog->sub_insn_off - prog->sec_insn_off;
    rec = new_prog_info + old_sz;
    rec_end = new_prog_info + new_sz;
    for (; rec < rec_end; rec += ext_info->rec_size) {
      __u32 *insn_off = rec;

      *insn_off = *insn_off / BPF_INSN_SZ + off_adj;
    }
    *prog_rec_sz = ext_info->rec_size;
    return 0;
  }

  return -ENOENT;
}

static int
reloc_prog_func_and_line_info(const struct bpf_object *obj,
            struct bpf_program *main_prog,
            const struct bpf_program *prog)
{
  int err;

  /* no .BTF.ext relocation if .BTF.ext is missing or kernel doesn't
   * supprot func/line info
   */
  if (!obj->btf_ext || !kernel_supports(obj, FEAT_BTF_FUNC))
    return 0;

  /* only attempt func info relocation if main program's func_info
   * relocation was successful
   */
  if (main_prog != prog && !main_prog->func_info)
    goto line_info;

  err = adjust_prog_btf_ext_info(obj, prog, &obj->btf_ext->func_info,
               &main_prog->func_info,
               &main_prog->func_info_cnt,
               &main_prog->func_info_rec_size);
  if (err) {
    if (err != -ENOENT) {
      pr_warn("prog '%s': error relocating .BTF.ext function info: %d\n",
        prog->name, err);
      return err;
    }
    if (main_prog->func_info) {
      /*
       * Some info has already been found but has problem
       * in the last btf_ext reloc. Must have to error out.
       */
      pr_warn("prog '%s': missing .BTF.ext function info.\n", prog->name);
      return err;
    }
    /* Have problem loading the very first info. Ignore the rest. */
    pr_warn("prog '%s': missing .BTF.ext function info for the main program, skipping all of .BTF.ext func info.\n",
      prog->name);
  }

line_info:
  /* don't relocate line info if main program's relocation failed */
  if (main_prog != prog && !main_prog->line_info)
    return 0;

  err = adjust_prog_btf_ext_info(obj, prog, &obj->btf_ext->line_info,
               &main_prog->line_info,
               &main_prog->line_info_cnt,
               &main_prog->line_info_rec_size);
  if (err) {
    if (err != -ENOENT) {
      pr_warn("prog '%s': error relocating .BTF.ext line info: %d\n",
        prog->name, err);
      return err;
    }
    if (main_prog->line_info) {
      /*
       * Some info has already been found but has problem
       * in the last btf_ext reloc. Must have to error out.
       */
      pr_warn("prog '%s': missing .BTF.ext line info.\n", prog->name);
      return err;
    }
    /* Have problem loading the very first info. Ignore the rest. */
    pr_warn("prog '%s': missing .BTF.ext line info for the main program, skipping all of .BTF.ext line info.\n",
      prog->name);
  }
  return 0;
}

static int cmp_relo_by_insn_idx(const void *key, const void *elem)
{
  size_t insn_idx = *(const size_t *)key;
  const struct reloc_desc *relo = elem;

  if (insn_idx == relo->insn_idx)
    return 0;
  return insn_idx < relo->insn_idx ? -1 : 1;
}

static struct reloc_desc *find_prog_insn_relo(const struct bpf_program *prog, size_t insn_idx)
{
  if (!prog->nr_reloc)
    return NULL;
  return bsearch(&insn_idx, prog->reloc_desc, prog->nr_reloc,
           sizeof(*prog->reloc_desc), cmp_relo_by_insn_idx);
}

static int append_subprog_relos(struct bpf_program *main_prog, struct bpf_program *subprog)
{
  int new_cnt = main_prog->nr_reloc + subprog->nr_reloc;
  struct reloc_desc *relos;
  int i;

  if (main_prog == subprog)
    return 0;
  relos = libbpf_reallocarray(main_prog->reloc_desc, new_cnt, sizeof(*relos));
  /* if new count is zero, reallocarray can return a valid NULL result;
   * in this case the previous pointer will be freed, so we *have to*
   * reassign old pointer to the new value (even if it's NULL)
   */
  if (!relos && new_cnt)
    return -ENOMEM;
  if (subprog->nr_reloc)
    memcpy(relos + main_prog->nr_reloc, subprog->reloc_desc,
           sizeof(*relos) * subprog->nr_reloc);

  for (i = main_prog->nr_reloc; i < new_cnt; i++)
    relos[i].insn_idx += subprog->sub_insn_off;
  /* After insn_idx adjustment the 'relos' array is still sorted
   * by insn_idx and doesn't break bsearch.
   */
  main_prog->reloc_desc = relos;
  main_prog->nr_reloc = new_cnt;
  return 0;
}

static int
bpf_object__append_subprog_code(struct bpf_object *obj, struct bpf_program *main_prog,
        struct bpf_program *subprog)
{
       struct bpf_insn *insns;
       size_t new_cnt;
       int err;

       subprog->sub_insn_off = main_prog->insns_cnt;

       new_cnt = main_prog->insns_cnt + subprog->insns_cnt;
       insns = libbpf_reallocarray(main_prog->insns, new_cnt, sizeof(*insns));
       if (!insns) {
               pr_warn("prog '%s': failed to realloc prog code\n", main_prog->name);
               return -ENOMEM;
       }
       main_prog->insns = insns;
       main_prog->insns_cnt = new_cnt;

       memcpy(main_prog->insns + subprog->sub_insn_off, subprog->insns,
              subprog->insns_cnt * sizeof(*insns));

       pr_debug("prog '%s': added %zu insns from sub-prog '%s'\n",
                main_prog->name, subprog->insns_cnt, subprog->name);

       /* The subprog insns are now appended. Append its relos too. */
       err = append_subprog_relos(main_prog, subprog);
       if (err)
               return err;
       return 0;
}

static int
bpf_object__reloc_code(struct bpf_object *obj, struct bpf_program *main_prog,
           struct bpf_program *prog)
{
  size_t sub_insn_idx, insn_idx;
  struct bpf_program *subprog;
  struct reloc_desc *relo;
  struct bpf_insn *insn;
  int err;

  err = reloc_prog_func_and_line_info(obj, main_prog, prog);
  if (err)
    return err;

  for (insn_idx = 0; insn_idx < prog->sec_insn_cnt; insn_idx++) {
    insn = &main_prog->insns[prog->sub_insn_off + insn_idx];
    if (!insn_is_subprog_call(insn) && !insn_is_pseudo_func(insn))
      continue;

    relo = find_prog_insn_relo(prog, insn_idx);
    if (relo && relo->type == RELO_EXTERN_CALL)
      /* kfunc relocations will be handled later
       * in bpf_object__relocate_data()
       */
      continue;
    if (relo && relo->type != RELO_CALL && relo->type != RELO_SUBPROG_ADDR) {
      pr_warn("prog '%s': unexpected relo for insn #%zu, type %d\n",
        prog->name, insn_idx, relo->type);
      return -LIBBPF_ERRNO__RELOC;
    }
    if (relo) {
      /* sub-program instruction index is a combination of
       * an offset of a symbol pointed to by relocation and
       * call instruction's imm field; for global functions,
       * call always has imm = -1, but for static functions
       * relocation is against STT_SECTION and insn->imm
       * points to a start of a static function
       *
       * for subprog addr relocation, the relo->sym_off + insn->imm is
       * the byte offset in the corresponding section.
       */
      if (relo->type == RELO_CALL)
        sub_insn_idx = relo->sym_off / BPF_INSN_SZ + insn->imm + 1;
      else
        sub_insn_idx = (relo->sym_off + insn->imm) / BPF_INSN_SZ;
    } else if (insn_is_pseudo_func(insn)) {
      /*
       * RELO_SUBPROG_ADDR relo is always emitted even if both
       * functions are in the same section, so it shouldn't reach here.
       */
      pr_warn("prog '%s': missing subprog addr relo for insn #%zu\n",
        prog->name, insn_idx);
      return -LIBBPF_ERRNO__RELOC;
    } else {
      /* if subprogram call is to a static function within
       * the same ELF section, there won't be any relocation
       * emitted, but it also means there is no additional
       * offset necessary, insns->imm is relative to
       * instruction's original position within the section
       */
      sub_insn_idx = prog->sec_insn_off + insn_idx + insn->imm + 1;
    }

    /* we enforce that sub-programs should be in .text section */
    subprog = find_prog_by_sec_insn(obj, obj->efile.text_shndx, sub_insn_idx);
    if (!subprog) {
      pr_warn("prog '%s': no .text section found yet sub-program call exists\n",
        prog->name);
      return -LIBBPF_ERRNO__RELOC;
    }

    /* if it's the first call instruction calling into this
     * subprogram (meaning this subprog hasn't been processed
     * yet) within the context of current main program:
     *   - append it at the end of main program's instructions blog;
     *   - process is recursively, while current program is put on hold;
     *   - if that subprogram calls some other not yet processes
     *   subprogram, same thing will happen recursively until
     *   there are no more unprocesses subprograms left to append
     *   and relocate.
     */
    if (subprog->sub_insn_off == 0) {
      err = bpf_object__append_subprog_code(obj, main_prog, subprog);
      if (err)
        return err;
      err = bpf_object__reloc_code(obj, main_prog, subprog);
      if (err)
        return err;
    }

    /* main_prog->insns memory could have been re-allocated, so
     * calculate pointer again
     */
    insn = &main_prog->insns[prog->sub_insn_off + insn_idx];
    /* calculate correct instruction position within current main
     * prog; each main prog can have a different set of
     * subprograms appended (potentially in different order as
     * well), so position of any subprog can be different for
     * different main programs
     */
    insn->imm = subprog->sub_insn_off - (prog->sub_insn_off + insn_idx) - 1;

    pr_debug("prog '%s': insn #%zu relocated, imm %d points to subprog '%s' (now at %zu offset)\n",
       prog->name, insn_idx, insn->imm, subprog->name, subprog->sub_insn_off);
  }

  return 0;
}

/*
 * Relocate sub-program calls.
 *
 * Algorithm operates as follows. Each entry-point BPF program (referred to as
 * main prog) is processed separately. For each subprog (non-entry functions,
 * that can be called from either entry progs or other subprogs) gets their
 * sub_insn_off reset to zero. This serves as indicator that this subprogram
 * hasn't been yet appended and relocated within current main prog. Once its
 * relocated, sub_insn_off will point at the position within current main prog
 * where given subprog was appended. This will further be used to relocate all
 * the call instructions jumping into this subprog.
 *
 * We start with main program and process all call instructions. If the call
 * is into a subprog that hasn't been processed (i.e., subprog->sub_insn_off
 * is zero), subprog instructions are appended at the end of main program's
 * instruction array. Then main program is "put on hold" while we recursively
 * process newly appended subprogram. If that subprogram calls into another
 * subprogram that hasn't been appended, new subprogram is appended again to
 * the *main* prog's instructions (subprog's instructions are always left
 * untouched, as they need to be in unmodified state for subsequent main progs
 * and subprog instructions are always sent only as part of a main prog) and
 * the process continues recursively. Once all the subprogs called from a main
 * prog or any of its subprogs are appended (and relocated), all their
 * positions within finalized instructions array are known, so it's easy to
 * rewrite call instructions with correct relative offsets, corresponding to
 * desired target subprog.
 *
 * Its important to realize that some subprogs might not be called from some
 * main prog and any of its called/used subprogs. Those will keep their
 * subprog->sub_insn_off as zero at all times and won't be appended to current
 * main prog and won't be relocated within the context of current main prog.
 * They might still be used from other main progs later.
 *
 * Visually this process can be shown as below. Suppose we have two main
 * programs mainA and mainB and BPF object contains three subprogs: subA,
 * subB, and subC. mainA calls only subA, mainB calls only subC, but subA and
 * subC both call subB:
 *
 *        +--------+ +-------+
 *        |        v v       |
 *     +--+---+ +--+-+-+ +---+--+
 *     | subA | | subB | | subC |
 *     +--+---+ +------+ +---+--+
 *        ^                  ^
 *        |                  |
 *    +---+-------+   +------+----+
 *    |   mainA   |   |   mainB   |
 *    +-----------+   +-----------+
 *
 * We'll start relocating mainA, will find subA, append it and start
 * processing sub A recursively:
 *
 *    +-----------+------+
 *    |   mainA   | subA |
 *    +-----------+------+
 *
 * At this point we notice that subB is used from subA, so we append it and
 * relocate (there are no further subcalls from subB):
 *
 *    +-----------+------+------+
 *    |   mainA   | subA | subB |
 *    +-----------+------+------+
 *
 * At this point, we relocate subA calls, then go one level up and finish with
 * relocatin mainA calls. mainA is done.
 *
 * For mainB process is similar but results in different order. We start with
 * mainB and skip subA and subB, as mainB never calls them (at least
 * directly), but we see subC is needed, so we append and start processing it:
 *
 *    +-----------+------+
 *    |   mainB   | subC |
 *    +-----------+------+
 * Now we see subC needs subB, so we go back to it, append and relocate it:
 *
 *    +-----------+------+------+
 *    |   mainB   | subC | subB |
 *    +-----------+------+------+
 *
 * At this point we unwind recursion, relocate calls in subC, then in mainB.
 */
static int
bpf_object__relocate_calls(struct bpf_object *obj, struct bpf_program *prog)
{
  struct bpf_program *subprog;
  int i, err;

  /* mark all subprogs as not relocated (yet) within the context of
   * current main program
   */
  for (i = 0; i < obj->nr_programs; i++) {
    subprog = &obj->programs[i];
    if (!prog_is_subprog(obj, subprog))
      continue;

    subprog->sub_insn_off = 0;
  }

  err = bpf_object__reloc_code(obj, prog, prog);
  if (err)
    return err;

  return 0;
}

static void
bpf_object__free_relocs(struct bpf_object *obj)
{
  struct bpf_program *prog;
  int i;

  /* free up relocation descriptors */
  for (i = 0; i < obj->nr_programs; i++) {
    prog = &obj->programs[i];
    zfree(&prog->reloc_desc);
    prog->nr_reloc = 0;
  }
}

static int cmp_relocs(const void *_a, const void *_b)
{
  const struct reloc_desc *a = _a;
  const struct reloc_desc *b = _b;

  if (a->insn_idx != b->insn_idx)
    return a->insn_idx < b->insn_idx ? -1 : 1;

  /* no two relocations should have the same insn_idx, but ... */
  if (a->type != b->type)
    return a->type < b->type ? -1 : 1;

  return 0;
}

static void bpf_object__sort_relos(struct bpf_object *obj)
{
  int i;

  for (i = 0; i < obj->nr_programs; i++) {
    struct bpf_program *p = &obj->programs[i];

    if (!p->nr_reloc)
      continue;

    qsort(p->reloc_desc, p->nr_reloc, sizeof(*p->reloc_desc), cmp_relocs);
  }
}

static int
bpf_object__relocate(struct bpf_object *obj, const char *targ_btf_path)
{
  struct bpf_program *prog;
  size_t i, j;
  int err;

  if (obj->btf_ext) {
    err = bpf_object__relocate_core(obj, targ_btf_path);
    if (err) {
      pr_warn("failed to perform CO-RE relocations: %d\n",
        err);
      return err;
    }
    bpf_object__sort_relos(obj);
  }

  /* Before relocating calls pre-process relocations and mark
   * few ld_imm64 instructions that points to subprogs.
   * Otherwise bpf_object__reloc_code() later would have to consider
   * all ld_imm64 insns as relocation candidates. That would
   * reduce relocation speed, since amount of find_prog_insn_relo()
   * would increase and most of them will fail to find a relo.
   */
  for (i = 0; i < obj->nr_programs; i++) {
    prog = &obj->programs[i];
    for (j = 0; j < prog->nr_reloc; j++) {
      struct reloc_desc *relo = &prog->reloc_desc[j];
      struct bpf_insn *insn = &prog->insns[relo->insn_idx];

      /* mark the insn, so it's recognized by insn_is_pseudo_func() */
      if (relo->type == RELO_SUBPROG_ADDR)
        insn[0].src_reg = BPF_PSEUDO_FUNC;
    }
  }

  /* relocate subprogram calls and append used subprograms to main
   * programs; each copy of subprogram code needs to be relocated
   * differently for each main program, because its code location might
   * have changed.
   * Append subprog relos to main programs to allow data relos to be
   * processed after text is completely relocated.
   */
  for (i = 0; i < obj->nr_programs; i++) {
    prog = &obj->programs[i];
    /* sub-program's sub-calls are relocated within the context of
     * its main program only
     */
    if (prog_is_subprog(obj, prog))
      continue;
    if (!prog->autoload)
      continue;

    err = bpf_object__relocate_calls(obj, prog);
    if (err) {
      pr_warn("prog '%s': failed to relocate calls: %d\n",
        prog->name, err);
      return err;
    }

    /* Now, also append exception callback if it has not been done already. */
    if (prog->exception_cb_idx >= 0) {
      struct bpf_program *subprog = &obj->programs[prog->exception_cb_idx];

      /* Calling exception callback directly is disallowed, which the
       * verifier will reject later. In case it was processed already,
       * we can skip this step, otherwise for all other valid cases we
       * have to append exception callback now.
       */
      if (subprog->sub_insn_off == 0) {
        err = bpf_object__append_subprog_code(obj, prog, subprog);
        if (err)
          return err;
        err = bpf_object__reloc_code(obj, prog, subprog);
        if (err)
          return err;
      }
    }
  }
  /* Process data relos for main programs */
  for (i = 0; i < obj->nr_programs; i++) {
    prog = &obj->programs[i];
    if (prog_is_subprog(obj, prog))
      continue;
    if (!prog->autoload)
      continue;
    err = bpf_object__relocate_data(obj, prog);
    if (err) {
      pr_warn("prog '%s': failed to relocate data references: %d\n",
        prog->name, err);
      return err;
    }
  }

  return 0;
}

static int bpf_object__collect_st_ops_relos(struct bpf_object *obj,
              Elf64_Shdr *shdr, Elf_Data *data);

static int bpf_object__collect_map_relos(struct bpf_object *obj,
           Elf64_Shdr *shdr, Elf_Data *data)
{
  const int bpf_ptr_sz = 8, host_ptr_sz = sizeof(void *);
  int i, j, nrels, new_sz;
  const struct btf_var_secinfo *vi = NULL;
  const struct btf_type *sec, *var, *def;
  struct bpf_map *map = NULL, *targ_map = NULL;
  struct bpf_program *targ_prog = NULL;
  bool is_prog_array, is_map_in_map;
  const struct btf_member *member;
  const char *name, *mname, *type;
  unsigned int moff;
  Elf64_Sym *sym;
  Elf64_Rel *rel;
  void *tmp;

  if (!obj->efile.btf_maps_sec_btf_id || !obj->btf)
    return -EINVAL;
  sec = btf__type_by_id(obj->btf, obj->efile.btf_maps_sec_btf_id);
  if (!sec)
    return -EINVAL;

  nrels = shdr->sh_size / shdr->sh_entsize;
  for (i = 0; i < nrels; i++) {
    rel = elf_rel_by_idx(data, i);
    if (!rel) {
      pr_warn(".maps relo #%d: failed to get ELF relo\n", i);
      return -LIBBPF_ERRNO__FORMAT;
    }

    sym = elf_sym_by_idx(obj, ELF64_R_SYM(rel->r_info));
    if (!sym) {
      pr_warn(".maps relo #%d: symbol %zx not found\n",
        i, (size_t)ELF64_R_SYM(rel->r_info));
      return -LIBBPF_ERRNO__FORMAT;
    }
    name = elf_sym_str(obj, sym->st_name) ?: "<?>";

    pr_debug(".maps relo #%d: for %zd value %zd rel->r_offset %zu name %d ('%s')\n",
       i, (ssize_t)(rel->r_info >> 32), (size_t)sym->st_value,
       (size_t)rel->r_offset, sym->st_name, name);

    for (j = 0; j < obj->nr_maps; j++) {
      map = &obj->maps[j];
      if (map->sec_idx != obj->efile.btf_maps_shndx)
        continue;

      vi = btf_var_secinfos(sec) + map->btf_var_idx;
      if (vi->offset <= rel->r_offset &&
          rel->r_offset + bpf_ptr_sz <= vi->offset + vi->size)
        break;
    }
    if (j == obj->nr_maps) {
      pr_warn(".maps relo #%d: cannot find map '%s' at rel->r_offset %zu\n",
        i, name, (size_t)rel->r_offset);
      return -EINVAL;
    }

    is_map_in_map = bpf_map_type__is_map_in_map(map->def.type);
    is_prog_array = map->def.type == BPF_MAP_TYPE_PROG_ARRAY;
    type = is_map_in_map ? "map" : "prog";
    if (is_map_in_map) {
      if (sym->st_shndx != obj->efile.btf_maps_shndx) {
        pr_warn(".maps relo #%d: '%s' isn't a BTF-defined map\n",
          i, name);
        return -LIBBPF_ERRNO__RELOC;
      }
      if (map->def.type == BPF_MAP_TYPE_HASH_OF_MAPS &&
          map->def.key_size != sizeof(int)) {
        pr_warn(".maps relo #%d: hash-of-maps '%s' should have key size %zu.\n",
          i, map->name, sizeof(int));
        return -EINVAL;
      }
      targ_map = bpf_object__find_map_by_name(obj, name);
      if (!targ_map) {
        pr_warn(".maps relo #%d: '%s' isn't a valid map reference\n",
          i, name);
        return -ESRCH;
      }
    } else if (is_prog_array) {
      targ_prog = bpf_object__find_program_by_name(obj, name);
      if (!targ_prog) {
        pr_warn(".maps relo #%d: '%s' isn't a valid program reference\n",
          i, name);
        return -ESRCH;
      }
      if (targ_prog->sec_idx != sym->st_shndx ||
          targ_prog->sec_insn_off * 8 != sym->st_value ||
          prog_is_subprog(obj, targ_prog)) {
        pr_warn(".maps relo #%d: '%s' isn't an entry-point program\n",
          i, name);
        return -LIBBPF_ERRNO__RELOC;
      }
    } else {
      return -EINVAL;
    }

    var = btf__type_by_id(obj->btf, vi->type);
    def = skip_mods_and_typedefs(obj->btf, var->type, NULL);
    if (btf_vlen(def) == 0)
      return -EINVAL;
    member = btf_members(def) + btf_vlen(def) - 1;
    mname = btf__name_by_offset(obj->btf, member->name_off);
    if (strcmp(mname, "values"))
      return -EINVAL;

    moff = btf_member_bit_offset(def, btf_vlen(def) - 1) / 8;
    if (rel->r_offset - vi->offset < moff)
      return -EINVAL;

    moff = rel->r_offset - vi->offset - moff;
    /* here we use BPF pointer size, which is always 64 bit, as we
     * are parsing ELF that was built for BPF target
     */
    if (moff % bpf_ptr_sz)
      return -EINVAL;
    moff /= bpf_ptr_sz;
    if (moff >= map->init_slots_sz) {
      new_sz = moff + 1;
      tmp = libbpf_reallocarray(map->init_slots, new_sz, host_ptr_sz);
      if (!tmp)
        return -ENOMEM;
      map->init_slots = tmp;
      memset(map->init_slots + map->init_slots_sz, 0,
             (new_sz - map->init_slots_sz) * host_ptr_sz);
      map->init_slots_sz = new_sz;
    }
    map->init_slots[moff] = is_map_in_map ? (void *)targ_map : (void *)targ_prog;

    pr_debug(".maps relo #%d: map '%s' slot [%d] points to %s '%s'\n",
       i, map->name, moff, type, name);
  }

  return 0;
}

static int bpf_object__collect_relos(struct bpf_object *obj)
{
  int i, err;

  for (i = 0; i < obj->efile.sec_cnt; i++) {
    struct elf_sec_desc *sec_desc = &obj->efile.secs[i];
    Elf64_Shdr *shdr;
    Elf_Data *data;
    int idx;

    if (sec_desc->sec_type != SEC_RELO)
      continue;

    shdr = sec_desc->shdr;
    data = sec_desc->data;
    idx = shdr->sh_info;

    if (shdr->sh_type != SHT_REL) {
      pr_warn("internal error at %d\n", __LINE__);
      return -LIBBPF_ERRNO__INTERNAL;
    }

    if (idx == obj->efile.st_ops_shndx || idx == obj->efile.st_ops_link_shndx)
      err = bpf_object__collect_st_ops_relos(obj, shdr, data);
    else if (idx == obj->efile.btf_maps_shndx)
      err = bpf_object__collect_map_relos(obj, shdr, data);
    else
      err = bpf_object__collect_prog_relos(obj, shdr, data);
    if (err)
      return err;
  }

  bpf_object__sort_relos(obj);
  return 0;
}

static bool insn_is_helper_call(struct bpf_insn *insn, enum bpf_func_id *func_id)
{
  if (BPF_CLASS(insn->code) == BPF_JMP &&
      BPF_OP(insn->code) == BPF_CALL &&
      BPF_SRC(insn->code) == BPF_K &&
      insn->src_reg == 0 &&
      insn->dst_reg == 0) {
        *func_id = insn->imm;
        return true;
  }
  return false;
}

static int bpf_object__sanitize_prog(struct bpf_object *obj, struct bpf_program *prog)
{
  struct bpf_insn *insn = prog->insns;
  enum bpf_func_id func_id;
  int i;

  if (obj->gen_loader)
    return 0;

  for (i = 0; i < prog->insns_cnt; i++, insn++) {
    if (!insn_is_helper_call(insn, &func_id))
      continue;

    /* on kernels that don't yet support
     * bpf_probe_read_{kernel,user}[_str] helpers, fall back
     * to bpf_probe_read() which works well for old kernels
     */
    switch (func_id) {
    case BPF_FUNC_probe_read_kernel:
    case BPF_FUNC_probe_read_user:
      if (!kernel_supports(obj, FEAT_PROBE_READ_KERN))
        insn->imm = BPF_FUNC_probe_read;
      break;
    case BPF_FUNC_probe_read_kernel_str:
    case BPF_FUNC_probe_read_user_str:
      if (!kernel_supports(obj, FEAT_PROBE_READ_KERN))
        insn->imm = BPF_FUNC_probe_read_str;
      break;
    default:
      break;
    }
  }
  return 0;
}

static int libbpf_find_attach_btf_id(struct bpf_program *prog, const char *attach_name,
             int *btf_obj_fd, int *btf_type_id);

/* this is called as prog->sec_def->prog_prepare_load_fn for libbpf-supported sec_defs */
static int libbpf_prepare_prog_load(struct bpf_program *prog,
            struct bpf_prog_load_opts *opts, long cookie)
{
  enum sec_def_flags def = cookie;

  /* old kernels might not support specifying expected_attach_type */
  if ((def & SEC_EXP_ATTACH_OPT) && !kernel_supports(prog->obj, FEAT_EXP_ATTACH_TYPE))
    opts->expected_attach_type = 0;

  if (def & SEC_SLEEPABLE)
    opts->prog_flags |= BPF_F_SLEEPABLE;

  if (prog->type == BPF_PROG_TYPE_XDP && (def & SEC_XDP_FRAGS))
    opts->prog_flags |= BPF_F_XDP_HAS_FRAGS;

  /* special check for usdt to use uprobe_multi link */
  if ((def & SEC_USDT) && kernel_supports(prog->obj, FEAT_UPROBE_MULTI_LINK))
    prog->expected_attach_type = BPF_TRACE_UPROBE_MULTI;

  if ((def & SEC_ATTACH_BTF) && !prog->attach_btf_id) {
    int btf_obj_fd = 0, btf_type_id = 0, err;
    const char *attach_name;

    attach_name = strchr(prog->sec_name, '/');
    if (!attach_name) {
      /* if BPF program is annotated with just SEC("fentry")
       * (or similar) without declaratively specifying
       * target, then it is expected that target will be
       * specified with bpf_program__set_attach_target() at
       * runtime before BPF object load step. If not, then
       * there is nothing to load into the kernel as BPF
       * verifier won't be able to validate BPF program
       * correctness anyways.
       */
      pr_warn("prog '%s': no BTF-based attach target is specified, use bpf_program__set_attach_target()\n",
        prog->name);
      return -EINVAL;
    }
    attach_name++; /* skip over / */

    err = libbpf_find_attach_btf_id(prog, attach_name, &btf_obj_fd, &btf_type_id);
    if (err)
      return err;

    /* cache resolved BTF FD and BTF type ID in the prog */
    prog->attach_btf_obj_fd = btf_obj_fd;
    prog->attach_btf_id = btf_type_id;

    /* but by now libbpf common logic is not utilizing
     * prog->atach_btf_obj_fd/prog->attach_btf_id anymore because
     * this callback is called after opts were populated by
     * libbpf, so this callback has to update opts explicitly here
     */
    opts->attach_btf_obj_fd = btf_obj_fd;
    opts->attach_btf_id = btf_type_id;
  }
  return 0;
}

static void fixup_verifier_log(struct bpf_program *prog, char *buf, size_t buf_sz);

static int bpf_object_load_prog(struct bpf_object *obj, struct bpf_program *prog,
        struct bpf_insn *insns, int insns_cnt,
        const char *license, __u32 kern_version, int *prog_fd)
{
  LIBBPF_OPTS(bpf_prog_load_opts, load_attr);
  const char *prog_name = NULL;
  char *cp, errmsg[STRERR_BUFSIZE];
  size_t log_buf_size = 0;
  char *log_buf = NULL, *tmp;
  int btf_fd, ret, err;
  bool own_log_buf = true;
  __u32 log_level = prog->log_level;

  if (prog->type == BPF_PROG_TYPE_UNSPEC) {
    /*
     * The program type must be set.  Most likely we couldn't find a proper
     * section definition at load time, and thus we didn't infer the type.
     */
    pr_warn("prog '%s': missing BPF prog type, check ELF section name '%s'\n",
      prog->name, prog->sec_name);
    return -EINVAL;
  }

  if (!insns || !insns_cnt)
    return -EINVAL;

  if (kernel_supports(obj, FEAT_PROG_NAME))
    prog_name = prog->name;
  load_attr.attach_prog_fd = prog->attach_prog_fd;
  load_attr.attach_btf_obj_fd = prog->attach_btf_obj_fd;
  load_attr.attach_btf_id = prog->attach_btf_id;
  load_attr.kern_version = kern_version;
  load_attr.prog_ifindex = prog->prog_ifindex;

  /* specify func_info/line_info only if kernel supports them */
  btf_fd = bpf_object__btf_fd(obj);
  if (btf_fd >= 0 && kernel_supports(obj, FEAT_BTF_FUNC)) {
    load_attr.prog_btf_fd = btf_fd;
    load_attr.func_info = prog->func_info;
    load_attr.func_info_rec_size = prog->func_info_rec_size;
    load_attr.func_info_cnt = prog->func_info_cnt;
    load_attr.line_info = prog->line_info;
    load_attr.line_info_rec_size = prog->line_info_rec_size;
    load_attr.line_info_cnt = prog->line_info_cnt;
  }
  load_attr.log_level = log_level;
  load_attr.prog_flags = prog->prog_flags;
  load_attr.fd_array = obj->fd_array;

  /* adjust load_attr if sec_def provides custom preload callback */
  if (prog->sec_def && prog->sec_def->prog_prepare_load_fn) {
    err = prog->sec_def->prog_prepare_load_fn(prog, &load_attr, prog->sec_def->cookie);
    if (err < 0) {
      pr_warn("prog '%s': failed to prepare load attributes: %d\n",
        prog->name, err);
      return err;
    }
    insns = prog->insns;
    insns_cnt = prog->insns_cnt;
  }

  /* allow prog_prepare_load_fn to change expected_attach_type */
  load_attr.expected_attach_type = prog->expected_attach_type;

  if (obj->gen_loader) {
    bpf_gen__prog_load(obj->gen_loader, prog->type, prog->name,
           license, insns, insns_cnt, &load_attr,
           prog - obj->programs);
    *prog_fd = -1;
    return 0;
  }

retry_load:
  /* if log_level is zero, we don't request logs initially even if
   * custom log_buf is specified; if the program load fails, then we'll
   * bump log_level to 1 and use either custom log_buf or we'll allocate
   * our own and retry the load to get details on what failed
   */
  if (log_level) {
    if (prog->log_buf) {
      log_buf = prog->log_buf;
      log_buf_size = prog->log_size;
      own_log_buf = false;
    } else if (obj->log_buf) {
      log_buf = obj->log_buf;
      log_buf_size = obj->log_size;
      own_log_buf = false;
    } else {
      log_buf_size = max((size_t)BPF_LOG_BUF_SIZE, log_buf_size * 2);
      tmp = realloc(log_buf, log_buf_size);
      if (!tmp) {
        ret = -ENOMEM;
        goto out;
      }
      log_buf = tmp;
      log_buf[0] = '\0';
      own_log_buf = true;
    }
  }

  load_attr.log_buf = log_buf;
  load_attr.log_size = log_buf_size;
  load_attr.log_level = log_level;

  ret = bpf_prog_load(prog->type, prog_name, license, insns, insns_cnt, &load_attr);
  if (ret >= 0) {
    if (log_level && own_log_buf) {
      pr_debug("prog '%s': -- BEGIN PROG LOAD LOG --\n%s-- END PROG LOAD LOG --\n",
         prog->name, log_buf);
    }

    if (obj->has_rodata && kernel_supports(obj, FEAT_PROG_BIND_MAP)) {
      struct bpf_map *map;
      int i;

      for (i = 0; i < obj->nr_maps; i++) {
        map = &prog->obj->maps[i];
        if (map->libbpf_type != LIBBPF_MAP_RODATA)
          continue;

        if (bpf_prog_bind_map(ret, bpf_map__fd(map), NULL)) {
          cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
          pr_warn("prog '%s': failed to bind map '%s': %s\n",
            prog->name, map->real_name, cp);
          /* Don't fail hard if can't bind rodata. */
        }
      }
    }

    *prog_fd = ret;
    ret = 0;
    goto out;
  }

  if (log_level == 0) {
    log_level = 1;
    goto retry_load;
  }
  /* On ENOSPC, increase log buffer size and retry, unless custom
   * log_buf is specified.
   * Be careful to not overflow u32, though. Kernel's log buf size limit
   * isn't part of UAPI so it can always be bumped to full 4GB. So don't
   * multiply by 2 unless we are sure we'll fit within 32 bits.
   * Currently, we'll get -EINVAL when we reach (UINT_MAX >> 2).
   */
  if (own_log_buf && errno == ENOSPC && log_buf_size <= UINT_MAX / 2)
    goto retry_load;

  ret = -errno;

  /* post-process verifier log to improve error descriptions */
  fixup_verifier_log(prog, log_buf, log_buf_size);

  cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
  pr_warn("prog '%s': BPF program load failed: %s\n", prog->name, cp);
  pr_perm_msg(ret);

  if (own_log_buf && log_buf && log_buf[0] != '\0') {
    pr_warn("prog '%s': -- BEGIN PROG LOAD LOG --\n%s-- END PROG LOAD LOG --\n",
      prog->name, log_buf);
  }

out:
  if (own_log_buf)
    free(log_buf);
  return ret;
}

static char *find_prev_line(char *buf, char *cur)
{
  char *p;

  if (cur == buf) /* end of a log buf */
    return NULL;

  p = cur - 1;
  while (p - 1 >= buf && *(p - 1) != '\n')
    p--;

  return p;
}

static void patch_log(char *buf, size_t buf_sz, size_t log_sz,
          char *orig, size_t orig_sz, const char *patch)
{
  /* size of the remaining log content to the right from the to-be-replaced part */
  size_t rem_sz = (buf + log_sz) - (orig + orig_sz);
  size_t patch_sz = strlen(patch);

  if (patch_sz != orig_sz) {
    /* If patch line(s) are longer than original piece of verifier log,
     * shift log contents by (patch_sz - orig_sz) bytes to the right
     * starting from after to-be-replaced part of the log.
     *
     * If patch line(s) are shorter than original piece of verifier log,
     * shift log contents by (orig_sz - patch_sz) bytes to the left
     * starting from after to-be-replaced part of the log
     *
     * We need to be careful about not overflowing available
     * buf_sz capacity. If that's the case, we'll truncate the end
     * of the original log, as necessary.
     */
    if (patch_sz > orig_sz) {
      if (orig + patch_sz >= buf + buf_sz) {
        /* patch is big enough to cover remaining space completely */
        patch_sz -= (orig + patch_sz) - (buf + buf_sz) + 1;
        rem_sz = 0;
      } else if (patch_sz - orig_sz > buf_sz - log_sz) {
        /* patch causes part of remaining log to be truncated */
        rem_sz -= (patch_sz - orig_sz) - (buf_sz - log_sz);
      }
    }
    /* shift remaining log to the right by calculated amount */
    memmove(orig + patch_sz, orig + orig_sz, rem_sz);
  }

  memcpy(orig, patch, patch_sz);
}

static void fixup_log_failed_core_relo(struct bpf_program *prog,
               char *buf, size_t buf_sz, size_t log_sz,
               char *line1, char *line2, char *line3)
{
  /* Expected log for failed and not properly guarded CO-RE relocation:
   * line1 -> 123: (85) call unknown#195896080
   * line2 -> invalid func unknown#195896080
   * line3 -> <anything else or end of buffer>
   *
   * "123" is the index of the instruction that was poisoned. We extract
   * instruction index to find corresponding CO-RE relocation and
   * replace this part of the log with more relevant information about
   * failed CO-RE relocation.
   */
  const struct bpf_core_relo *relo;
  struct bpf_core_spec spec;
  char patch[512], spec_buf[256];
  int insn_idx, err, spec_len;

  if (sscanf(line1, "%d: (%*d) call unknown#195896080\n", &insn_idx) != 1)
    return;

  relo = find_relo_core(prog, insn_idx);
  if (!relo)
    return;

  err = bpf_core_parse_spec(prog->name, prog->obj->btf, relo, &spec);
  if (err)
    return;

  spec_len = bpf_core_format_spec(spec_buf, sizeof(spec_buf), &spec);
  snprintf(patch, sizeof(patch),
     "%d: <invalid CO-RE relocation>\n"
     "failed to resolve CO-RE relocation %s%s\n",
     insn_idx, spec_buf, spec_len >= sizeof(spec_buf) ? "..." : "");

  patch_log(buf, buf_sz, log_sz, line1, line3 - line1, patch);
}

static void fixup_log_missing_map_load(struct bpf_program *prog,
               char *buf, size_t buf_sz, size_t log_sz,
               char *line1, char *line2, char *line3)
{
  /* Expected log for failed and not properly guarded map reference:
   * line1 -> 123: (85) call unknown#2001000345
   * line2 -> invalid func unknown#2001000345
   * line3 -> <anything else or end of buffer>
   *
   * "123" is the index of the instruction that was poisoned.
   * "345" in "2001000345" is a map index in obj->maps to fetch map name.
   */
  struct bpf_object *obj = prog->obj;
  const struct bpf_map *map;
  int insn_idx, map_idx;
  char patch[128];

  if (sscanf(line1, "%d: (%*d) call unknown#%d\n", &insn_idx, &map_idx) != 2)
    return;

  map_idx -= POISON_LDIMM64_MAP_BASE;
  if (map_idx < 0 || map_idx >= obj->nr_maps)
    return;
  map = &obj->maps[map_idx];

  snprintf(patch, sizeof(patch),
     "%d: <invalid BPF map reference>\n"
     "BPF map '%s' is referenced but wasn't created\n",
     insn_idx, map->name);

  patch_log(buf, buf_sz, log_sz, line1, line3 - line1, patch);
}

static void fixup_log_missing_kfunc_call(struct bpf_program *prog,
           char *buf, size_t buf_sz, size_t log_sz,
           char *line1, char *line2, char *line3)
{
  /* Expected log for failed and not properly guarded kfunc call:
   * line1 -> 123: (85) call unknown#2002000345
   * line2 -> invalid func unknown#2002000345
   * line3 -> <anything else or end of buffer>
   *
   * "123" is the index of the instruction that was poisoned.
   * "345" in "2002000345" is an extern index in obj->externs to fetch kfunc name.
   */
  struct bpf_object *obj = prog->obj;
  const struct extern_desc *ext;
  int insn_idx, ext_idx;
  char patch[128];

  if (sscanf(line1, "%d: (%*d) call unknown#%d\n", &insn_idx, &ext_idx) != 2)
    return;

  ext_idx -= POISON_CALL_KFUNC_BASE;
  if (ext_idx < 0 || ext_idx >= obj->nr_extern)
    return;
  ext = &obj->externs[ext_idx];

  snprintf(patch, sizeof(patch),
     "%d: <invalid kfunc call>\n"
     "kfunc '%s' is referenced but wasn't resolved\n",
     insn_idx, ext->name);

  patch_log(buf, buf_sz, log_sz, line1, line3 - line1, patch);
}

static void fixup_verifier_log(struct bpf_program *prog, char *buf, size_t buf_sz)
{
  /* look for familiar error patterns in last N lines of the log */
  const size_t max_last_line_cnt = 10;
  char *prev_line, *cur_line, *next_line;
  size_t log_sz;
  int i;

  if (!buf)
    return;

  log_sz = strlen(buf) + 1;
  next_line = buf + log_sz - 1;

  for (i = 0; i < max_last_line_cnt; i++, next_line = cur_line) {
    cur_line = find_prev_line(buf, next_line);
    if (!cur_line)
      return;

    if (str_has_pfx(cur_line, "invalid func unknown#195896080\n")) {
      prev_line = find_prev_line(buf, cur_line);
      if (!prev_line)
        continue;

      /* failed CO-RE relocation case */
      fixup_log_failed_core_relo(prog, buf, buf_sz, log_sz,
               prev_line, cur_line, next_line);
      return;
    } else if (str_has_pfx(cur_line, "invalid func unknown#"POISON_LDIMM64_MAP_PFX)) {
      prev_line = find_prev_line(buf, cur_line);
      if (!prev_line)
        continue;

      /* reference to uncreated BPF map */
      fixup_log_missing_map_load(prog, buf, buf_sz, log_sz,
               prev_line, cur_line, next_line);
      return;
    } else if (str_has_pfx(cur_line, "invalid func unknown#"POISON_CALL_KFUNC_PFX)) {
      prev_line = find_prev_line(buf, cur_line);
      if (!prev_line)
        continue;

      /* reference to unresolved kfunc */
      fixup_log_missing_kfunc_call(prog, buf, buf_sz, log_sz,
                 prev_line, cur_line, next_line);
      return;
    }
  }
}

static int bpf_program_record_relos(struct bpf_program *prog)
{
  struct bpf_object *obj = prog->obj;
  int i;

  for (i = 0; i < prog->nr_reloc; i++) {
    struct reloc_desc *relo = &prog->reloc_desc[i];
    struct extern_desc *ext = &obj->externs[relo->ext_idx];
    int kind;

    switch (relo->type) {
    case RELO_EXTERN_LD64:
      if (ext->type != EXT_KSYM)
        continue;
      kind = btf_is_var(btf__type_by_id(obj->btf, ext->btf_id)) ?
        BTF_KIND_VAR : BTF_KIND_FUNC;
      bpf_gen__record_extern(obj->gen_loader, ext->name,
                 ext->is_weak, !ext->ksym.type_id,
                 true, kind, relo->insn_idx);
      break;
    case RELO_EXTERN_CALL:
      bpf_gen__record_extern(obj->gen_loader, ext->name,
                 ext->is_weak, false, false, BTF_KIND_FUNC,
                 relo->insn_idx);
      break;
    case RELO_CORE: {
      struct bpf_core_relo cr = {
        .insn_off = relo->insn_idx * 8,
        .type_id = relo->core_relo->type_id,
        .access_str_off = relo->core_relo->access_str_off,
        .kind = relo->core_relo->kind,
      };

      bpf_gen__record_relo_core(obj->gen_loader, &cr);
      break;
    }
    default:
      continue;
    }
  }
  return 0;
}

static int
bpf_object__load_progs(struct bpf_object *obj, int log_level)
{
  struct bpf_program *prog;
  size_t i;
  int err;

  for (i = 0; i < obj->nr_programs; i++) {
    prog = &obj->programs[i];
    err = bpf_object__sanitize_prog(obj, prog);
    if (err)
      return err;
  }

  for (i = 0; i < obj->nr_programs; i++) {
    prog = &obj->programs[i];
    if (prog_is_subprog(obj, prog))
      continue;
    if (!prog->autoload) {
      pr_debug("prog '%s': skipped loading\n", prog->name);
      continue;
    }
    prog->log_level |= log_level;

    if (obj->gen_loader)
      bpf_program_record_relos(prog);

    err = bpf_object_load_prog(obj, prog, prog->insns, prog->insns_cnt,
             obj->license, obj->kern_version, &prog->fd);
    if (err) {
      pr_warn("prog '%s': failed to load: %d\n", prog->name, err);
      return err;
    }
  }

  bpf_object__free_relocs(obj);
  return 0;
}

static const struct bpf_sec_def *find_sec_def(const char *sec_name);

static int bpf_object_init_progs(struct bpf_object *obj, const struct bpf_object_open_opts *opts)
{
  struct bpf_program *prog;
  int err;

  bpf_object__for_each_program(prog, obj) {
    prog->sec_def = find_sec_def(prog->sec_name);
    if (!prog->sec_def) {
      /* couldn't guess, but user might manually specify */
      pr_debug("prog '%s': unrecognized ELF section name '%s'\n",
        prog->name, prog->sec_name);
      continue;
    }

    prog->type = prog->sec_def->prog_type;
    prog->expected_attach_type = prog->sec_def->expected_attach_type;

    /* sec_def can have custom callback which should be called
     * after bpf_program is initialized to adjust its properties
     */
    if (prog->sec_def->prog_setup_fn) {
      err = prog->sec_def->prog_setup_fn(prog, prog->sec_def->cookie);
      if (err < 0) {
        pr_warn("prog '%s': failed to initialize: %d\n",
          prog->name, err);
        return err;
      }
    }
  }

  return 0;
}

static struct bpf_object *bpf_object_open(const char *path, const void *obj_buf, size_t obj_buf_sz,
            const struct bpf_object_open_opts *opts)
{
  const char *obj_name, *kconfig, *btf_tmp_path;
  struct bpf_object *obj;
  char tmp_name[64];
  int err;
  char *log_buf;
  size_t log_size;
  __u32 log_level;

  if (elf_version(EV_CURRENT) == EV_NONE) {
    pr_warn("failed to init libelf for %s\n",
      path ? : "(mem buf)");
    return ERR_PTR(-LIBBPF_ERRNO__LIBELF);
  }

  if (!OPTS_VALID(opts, bpf_object_open_opts))
    return ERR_PTR(-EINVAL);

  obj_name = OPTS_GET(opts, object_name, NULL);
  if (obj_buf) {
    if (!obj_name) {
      snprintf(tmp_name, sizeof(tmp_name), "%lx-%lx",
         (unsigned long)obj_buf,
         (unsigned long)obj_buf_sz);
      obj_name = tmp_name;
    }
    path = obj_name;
    pr_debug("loading object '%s' from buffer\n", obj_name);
  }

  log_buf = OPTS_GET(opts, kernel_log_buf, NULL);
  log_size = OPTS_GET(opts, kernel_log_size, 0);
  log_level = OPTS_GET(opts, kernel_log_level, 0);
  if (log_size > UINT_MAX)
    return ERR_PTR(-EINVAL);
  if (log_size && !log_buf)
    return ERR_PTR(-EINVAL);

  obj = bpf_object__new(path, obj_buf, obj_buf_sz, obj_name);
  if (IS_ERR(obj))
    return obj;

  obj->log_buf = log_buf;
  obj->log_size = log_size;
  obj->log_level = log_level;

  btf_tmp_path = OPTS_GET(opts, btf_custom_path, NULL);
  if (btf_tmp_path) {
    if (strlen(btf_tmp_path) >= PATH_MAX) {
      err = -ENAMETOOLONG;
      goto out;
    }
    obj->btf_custom_path = strdup(btf_tmp_path);
    if (!obj->btf_custom_path) {
      err = -ENOMEM;
      goto out;
    }
  }

  kconfig = OPTS_GET(opts, kconfig, NULL);
  if (kconfig) {
    obj->kconfig = strdup(kconfig);
    if (!obj->kconfig) {
      err = -ENOMEM;
      goto out;
    }
  }

  err = bpf_object__elf_init(obj);
  err = err ? : bpf_object__check_endianness(obj);
  err = err ? : bpf_object__elf_collect(obj);
  err = err ? : bpf_object__collect_externs(obj);
  err = err ? : bpf_object_fixup_btf(obj);
  err = err ? : bpf_object__init_maps(obj, opts);
  err = err ? : bpf_object_init_progs(obj, opts);
  err = err ? : bpf_object__collect_relos(obj);
  if (err)
    goto out;

  bpf_object__elf_finish(obj);

  return obj;
out:
  bpf_object__close(obj);
  return ERR_PTR(err);
}

struct bpf_object *
bpf_object__open_file(const char *path, const struct bpf_object_open_opts *opts)
{
  if (!path)
    return libbpf_err_ptr(-EINVAL);

  pr_debug("loading %s\n", path);

  return libbpf_ptr(bpf_object_open(path, NULL, 0, opts));
}

struct bpf_object *bpf_object__open(const char *path)
{
  return bpf_object__open_file(path, NULL);
}

struct bpf_object *
bpf_object__open_mem(const void *obj_buf, size_t obj_buf_sz,
         const struct bpf_object_open_opts *opts)
{
  if (!obj_buf || obj_buf_sz == 0)
    return libbpf_err_ptr(-EINVAL);

  return libbpf_ptr(bpf_object_open(NULL, obj_buf, obj_buf_sz, opts));
}

static int bpf_object_unload(struct bpf_object *obj)
{
  size_t i;

  if (!obj)
    return libbpf_err(-EINVAL);

  for (i = 0; i < obj->nr_maps; i++) {
    zclose(obj->maps[i].fd);
    if (obj->maps[i].st_ops)
      zfree(&obj->maps[i].st_ops->kern_vdata);
  }

  for (i = 0; i < obj->nr_programs; i++)
    bpf_program__unload(&obj->programs[i]);

  return 0;
}

static int bpf_object__sanitize_maps(struct bpf_object *obj)
{
  struct bpf_map *m;

  bpf_object__for_each_map(m, obj) {
    if (!bpf_map__is_internal(m))
      continue;
    if (!kernel_supports(obj, FEAT_ARRAY_MMAP))
      m->def.map_flags &= ~BPF_F_MMAPABLE;
  }

  return 0;
}

int libbpf_kallsyms_parse(kallsyms_cb_t cb, void *ctx)
{
  char sym_type, sym_name[500];
  unsigned long long sym_addr;
  int ret, err = 0;
  FILE *f;

  f = fopen("/proc/kallsyms", "re");
  if (!f) {
    err = -errno;
    pr_warn("failed to open /proc/kallsyms: %d\n", err);
    return err;
  }

  while (true) {
    ret = fscanf(f, "%llx %c %499s%*[^\n]\n",
           &sym_addr, &sym_type, sym_name);
    if (ret == EOF && feof(f))
      break;
    if (ret != 3) {
      pr_warn("failed to read kallsyms entry: %d\n", ret);
      err = -EINVAL;
      break;
    }

    err = cb(sym_addr, sym_type, sym_name, ctx);
    if (err)
      break;
  }

  fclose(f);
  return err;
}

static int kallsyms_cb(unsigned long long sym_addr, char sym_type,
           const char *sym_name, void *ctx)
{
  struct bpf_object *obj = ctx;
  const struct btf_type *t;
  struct extern_desc *ext;

  ext = find_extern_by_name(obj, sym_name);
  if (!ext || ext->type != EXT_KSYM)
    return 0;

  t = btf__type_by_id(obj->btf, ext->btf_id);
  if (!btf_is_var(t))
    return 0;

  if (ext->is_set && ext->ksym.addr != sym_addr) {
    pr_warn("extern (ksym) '%s': resolution is ambiguous: 0x%llx or 0x%llx\n",
      sym_name, ext->ksym.addr, sym_addr);
    return -EINVAL;
  }
  if (!ext->is_set) {
    ext->is_set = true;
    ext->ksym.addr = sym_addr;
    pr_debug("extern (ksym) '%s': set to 0x%llx\n", sym_name, sym_addr);
  }
  return 0;
}

static int bpf_object__read_kallsyms_file(struct bpf_object *obj)
{
  return libbpf_kallsyms_parse(kallsyms_cb, obj);
}

static int find_ksym_btf_id(struct bpf_object *obj, const char *ksym_name,
          __u16 kind, struct btf **res_btf,
          struct module_btf **res_mod_btf)
{
  struct module_btf *mod_btf;
  struct btf *btf;
  int i, id, err;

  btf = obj->btf_vmlinux;
  mod_btf = NULL;
  id = btf__find_by_name_kind(btf, ksym_name, kind);

  if (id == -ENOENT) {
    err = load_module_btfs(obj);
    if (err)
      return err;

    for (i = 0; i < obj->btf_module_cnt; i++) {
      /* we assume module_btf's BTF FD is always >0 */
      mod_btf = &obj->btf_modules[i];
      btf = mod_btf->btf;
      id = btf__find_by_name_kind_own(btf, ksym_name, kind);
      if (id != -ENOENT)
        break;
    }
  }
  if (id <= 0)
    return -ESRCH;

  *res_btf = btf;
  *res_mod_btf = mod_btf;
  return id;
}

static int bpf_object__resolve_ksym_var_btf_id(struct bpf_object *obj,
                 struct extern_desc *ext)
{
  const struct btf_type *targ_var, *targ_type;
  __u32 targ_type_id, local_type_id;
  struct module_btf *mod_btf = NULL;
  const char *targ_var_name;
  struct btf *btf = NULL;
  int id, err;

  id = find_ksym_btf_id(obj, ext->name, BTF_KIND_VAR, &btf, &mod_btf);
  if (id < 0) {
    if (id == -ESRCH && ext->is_weak)
      return 0;
    pr_warn("extern (var ksym) '%s': not found in kernel BTF\n",
      ext->name);
    return id;
  }

  /* find local type_id */
  local_type_id = ext->ksym.type_id;

  /* find target type_id */
  targ_var = btf__type_by_id(btf, id);
  targ_var_name = btf__name_by_offset(btf, targ_var->name_off);
  targ_type = skip_mods_and_typedefs(btf, targ_var->type, &targ_type_id);

  err = bpf_core_types_are_compat(obj->btf, local_type_id,
          btf, targ_type_id);
  if (err <= 0) {
    const struct btf_type *local_type;
    const char *targ_name, *local_name;

    local_type = btf__type_by_id(obj->btf, local_type_id);
    local_name = btf__name_by_offset(obj->btf, local_type->name_off);
    targ_name = btf__name_by_offset(btf, targ_type->name_off);

    pr_warn("extern (var ksym) '%s': incompatible types, expected [%d] %s %s, but kernel has [%d] %s %s\n",
      ext->name, local_type_id,
      btf_kind_str(local_type), local_name, targ_type_id,
      btf_kind_str(targ_type), targ_name);
    return -EINVAL;
  }

  ext->is_set = true;
  ext->ksym.kernel_btf_obj_fd = mod_btf ? mod_btf->fd : 0;
  ext->ksym.kernel_btf_id = id;
  pr_debug("extern (var ksym) '%s': resolved to [%d] %s %s\n",
     ext->name, id, btf_kind_str(targ_var), targ_var_name);

  return 0;
}

static int bpf_object__resolve_ksym_func_btf_id(struct bpf_object *obj,
            struct extern_desc *ext)
{
  int local_func_proto_id, kfunc_proto_id, kfunc_id;
  struct module_btf *mod_btf = NULL;
  const struct btf_type *kern_func;
  struct btf *kern_btf = NULL;
  int ret;

  local_func_proto_id = ext->ksym.type_id;

  kfunc_id = find_ksym_btf_id(obj, ext->essent_name ?: ext->name, BTF_KIND_FUNC, &kern_btf,
            &mod_btf);
  if (kfunc_id < 0) {
    if (kfunc_id == -ESRCH && ext->is_weak)
      return 0;
    pr_warn("extern (func ksym) '%s': not found in kernel or module BTFs\n",
      ext->name);
    return kfunc_id;
  }

  kern_func = btf__type_by_id(kern_btf, kfunc_id);
  kfunc_proto_id = kern_func->type;

  ret = bpf_core_types_are_compat(obj->btf, local_func_proto_id,
          kern_btf, kfunc_proto_id);
  if (ret <= 0) {
    if (ext->is_weak)
      return 0;

    pr_warn("extern (func ksym) '%s': func_proto [%d] incompatible with %s [%d]\n",
      ext->name, local_func_proto_id,
      mod_btf ? mod_btf->name : "vmlinux", kfunc_proto_id);
    return -EINVAL;
  }

  /* set index for module BTF fd in fd_array, if unset */
  if (mod_btf && !mod_btf->fd_array_idx) {
    /* insn->off is s16 */
    if (obj->fd_array_cnt == INT16_MAX) {
      pr_warn("extern (func ksym) '%s': module BTF fd index %d too big to fit in bpf_insn offset\n",
        ext->name, mod_btf->fd_array_idx);
      return -E2BIG;
    }
    /* Cannot use index 0 for module BTF fd */
    if (!obj->fd_array_cnt)
      obj->fd_array_cnt = 1;

    ret = libbpf_ensure_mem((void **)&obj->fd_array, &obj->fd_array_cap, sizeof(int),
          obj->fd_array_cnt + 1);
    if (ret)
      return ret;
    mod_btf->fd_array_idx = obj->fd_array_cnt;
    /* we assume module BTF FD is always >0 */
    obj->fd_array[obj->fd_array_cnt++] = mod_btf->fd;
  }

  ext->is_set = true;
  ext->ksym.kernel_btf_id = kfunc_id;
  ext->ksym.btf_fd_idx = mod_btf ? mod_btf->fd_array_idx : 0;
  /* Also set kernel_btf_obj_fd to make sure that bpf_object__relocate_data()
   * populates FD into ld_imm64 insn when it's used to point to kfunc.
   * {kernel_btf_id, btf_fd_idx} -> fixup bpf_call.
   * {kernel_btf_id, kernel_btf_obj_fd} -> fixup ld_imm64.
   */
  ext->ksym.kernel_btf_obj_fd = mod_btf ? mod_btf->fd : 0;
  pr_debug("extern (func ksym) '%s': resolved to %s [%d]\n",
     ext->name, mod_btf ? mod_btf->name : "vmlinux", kfunc_id);

  return 0;
}

static int bpf_object__resolve_ksyms_btf_id(struct bpf_object *obj)
{
  const struct btf_type *t;
  struct extern_desc *ext;
  int i, err;

  for (i = 0; i < obj->nr_extern; i++) {
    ext = &obj->externs[i];
    if (ext->type != EXT_KSYM || !ext->ksym.type_id)
      continue;

    if (obj->gen_loader) {
      ext->is_set = true;
      ext->ksym.kernel_btf_obj_fd = 0;
      ext->ksym.kernel_btf_id = 0;
      continue;
    }
    t = btf__type_by_id(obj->btf, ext->btf_id);
    if (btf_is_var(t))
      err = bpf_object__resolve_ksym_var_btf_id(obj, ext);
    else
      err = bpf_object__resolve_ksym_func_btf_id(obj, ext);
    if (err)
      return err;
  }
  return 0;
}

static int bpf_object__resolve_externs(struct bpf_object *obj,
               const char *extra_kconfig)
{
  bool need_config = false, need_kallsyms = false;
  bool need_vmlinux_btf = false;
  struct extern_desc *ext;
  void *kcfg_data = NULL;
  int err, i;

  if (obj->nr_extern == 0)
    return 0;

  if (obj->kconfig_map_idx >= 0)
    kcfg_data = obj->maps[obj->kconfig_map_idx].mmaped;

  for (i = 0; i < obj->nr_extern; i++) {
    ext = &obj->externs[i];

    if (ext->type == EXT_KSYM) {
      if (ext->ksym.type_id)
        need_vmlinux_btf = true;
      else
        need_kallsyms = true;
      continue;
    } else if (ext->type == EXT_KCFG) {
      void *ext_ptr = kcfg_data + ext->kcfg.data_off;
      __u64 value = 0;

      /* Kconfig externs need actual /proc/config.gz */
      if (str_has_pfx(ext->name, "CONFIG_")) {
        need_config = true;
        continue;
      }

      /* Virtual kcfg externs are customly handled by libbpf */
      if (strcmp(ext->name, "LINUX_KERNEL_VERSION") == 0) {
        value = get_kernel_version();
        if (!value) {
          pr_warn("extern (kcfg) '%s': failed to get kernel version\n", ext->name);
          return -EINVAL;
        }
      } else if (strcmp(ext->name, "LINUX_HAS_BPF_COOKIE") == 0) {
        value = kernel_supports(obj, FEAT_BPF_COOKIE);
      } else if (strcmp(ext->name, "LINUX_HAS_SYSCALL_WRAPPER") == 0) {
        value = kernel_supports(obj, FEAT_SYSCALL_WRAPPER);
      } else if (!str_has_pfx(ext->name, "LINUX_") || !ext->is_weak) {
        /* Currently libbpf supports only CONFIG_ and LINUX_ prefixed
         * __kconfig externs, where LINUX_ ones are virtual and filled out
         * customly by libbpf (their values don't come from Kconfig).
         * If LINUX_xxx variable is not recognized by libbpf, but is marked
         * __weak, it defaults to zero value, just like for CONFIG_xxx
         * externs.
         */
        pr_warn("extern (kcfg) '%s': unrecognized virtual extern\n", ext->name);
        return -EINVAL;
      }

      err = set_kcfg_value_num(ext, ext_ptr, value);
      if (err)
        return err;
      pr_debug("extern (kcfg) '%s': set to 0x%llx\n",
         ext->name, (long long)value);
    } else {
      pr_warn("extern '%s': unrecognized extern kind\n", ext->name);
      return -EINVAL;
    }
  }
  if (need_config && extra_kconfig) {
    err = bpf_object__read_kconfig_mem(obj, extra_kconfig, kcfg_data);
    if (err)
      return -EINVAL;
    need_config = false;
    for (i = 0; i < obj->nr_extern; i++) {
      ext = &obj->externs[i];
      if (ext->type == EXT_KCFG && !ext->is_set) {
        need_config = true;
        break;
      }
    }
  }
  if (need_config) {
    err = bpf_object__read_kconfig_file(obj, kcfg_data);
    if (err)
      return -EINVAL;
  }
  if (need_kallsyms) {
    err = bpf_object__read_kallsyms_file(obj);
    if (err)
      return -EINVAL;
  }
  if (need_vmlinux_btf) {
    err = bpf_object__resolve_ksyms_btf_id(obj);
    if (err)
      return -EINVAL;
  }
  for (i = 0; i < obj->nr_extern; i++) {
    ext = &obj->externs[i];

    if (!ext->is_set && !ext->is_weak) {
      pr_warn("extern '%s' (strong): not resolved\n", ext->name);
      return -ESRCH;
    } else if (!ext->is_set) {
      pr_debug("extern '%s' (weak): not resolved, defaulting to zero\n",
         ext->name);
    }
  }

  return 0;
}

static void bpf_map_prepare_vdata(const struct bpf_map *map)
{
  struct bpf_struct_ops *st_ops;
  __u32 i;

  st_ops = map->st_ops;
  for (i = 0; i < btf_vlen(st_ops->type); i++) {
    struct bpf_program *prog = st_ops->progs[i];
    void *kern_data;
    int prog_fd;

    if (!prog)
      continue;

    prog_fd = bpf_program__fd(prog);
    kern_data = st_ops->kern_vdata + st_ops->kern_func_off[i];
    *(unsigned long *)kern_data = prog_fd;
  }
}

static int bpf_object_prepare_struct_ops(struct bpf_object *obj)
{
  int i;

  for (i = 0; i < obj->nr_maps; i++)
    if (bpf_map__is_struct_ops(&obj->maps[i]))
      bpf_map_prepare_vdata(&obj->maps[i]);

  return 0;
}

static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const char *target_btf_path)
{
  int err, i;

  if (!obj)
    return libbpf_err(-EINVAL);

  if (obj->loaded) {
    pr_warn("object '%s': load can't be attempted twice\n", obj->name);
    return libbpf_err(-EINVAL);
  }

  if (obj->gen_loader)
    bpf_gen__init(obj->gen_loader, extra_log_level, obj->nr_programs, obj->nr_maps);

  err = bpf_object__probe_loading(obj);
  err = err ? : bpf_object__load_vmlinux_btf(obj, false);
  err = err ? : bpf_object__resolve_externs(obj, obj->kconfig);
  err = err ? : bpf_object__sanitize_and_load_btf(obj);
  err = err ? : bpf_object__sanitize_maps(obj);
  err = err ? : bpf_object__init_kern_struct_ops_maps(obj);
  err = err ? : bpf_object__create_maps(obj);
  err = err ? : bpf_object__relocate(obj, obj->btf_custom_path ? : target_btf_path);
  err = err ? : bpf_object__load_progs(obj, extra_log_level);
  err = err ? : bpf_object_init_prog_arrays(obj);
  err = err ? : bpf_object_prepare_struct_ops(obj);

  if (obj->gen_loader) {
    /* reset FDs */
    if (obj->btf)
      btf__set_fd(obj->btf, -1);
    for (i = 0; i < obj->nr_maps; i++)
      obj->maps[i].fd = -1;
    if (!err)
      err = bpf_gen__finish(obj->gen_loader, obj->nr_programs, obj->nr_maps);
  }

  /* clean up fd_array */
  zfree(&obj->fd_array);

  /* clean up module BTFs */
  for (i = 0; i < obj->btf_module_cnt; i++) {
    close(obj->btf_modules[i].fd);
    btf__free(obj->btf_modules[i].btf);
    free(obj->btf_modules[i].name);
  }
  free(obj->btf_modules);

  /* clean up vmlinux BTF */
  btf__free(obj->btf_vmlinux);
  obj->btf_vmlinux = NULL;

  obj->loaded = true; /* doesn't matter if successfully or not */

  if (err)
    goto out;

  return 0;
out:
  /* unpin any maps that were auto-pinned during load */
  for (i = 0; i < obj->nr_maps; i++)
    if (obj->maps[i].pinned && !obj->maps[i].reused)
      bpf_map__unpin(&obj->maps[i], NULL);

  bpf_object_unload(obj);
  pr_warn("failed to load object '%s'\n", obj->path);
  return libbpf_err(err);
}

int bpf_object__load(struct bpf_object *obj)
{
  return bpf_object_load(obj, 0, NULL);
}

static int make_parent_dir(const char *path)
{
  char *cp, errmsg[STRERR_BUFSIZE];
  char *dname, *dir;
  int err = 0;

  dname = strdup(path);
  if (dname == NULL)
    return -ENOMEM;

  dir = dirname(dname);
  if (mkdir(dir, 0700) && errno != EEXIST)
    err = -errno;

  free(dname);
  if (err) {
    cp = libbpf_strerror_r(-err, errmsg, sizeof(errmsg));
    pr_warn("failed to mkdir %s: %s\n", path, cp);
  }
  return err;
}

static int check_path(const char *path)
{
  char *cp, errmsg[STRERR_BUFSIZE];
  struct statfs st_fs;
  char *dname, *dir;
  int err = 0;

  if (path == NULL)
    return -EINVAL;

  dname = strdup(path);
  if (dname == NULL)
    return -ENOMEM;

  dir = dirname(dname);
  if (statfs(dir, &st_fs)) {
    cp = libbpf_strerror_r(errno, errmsg, sizeof(errmsg));
    pr_warn("failed to statfs %s: %s\n", dir, cp);
    err = -errno;
  }
  free(dname);

  if (!err && st_fs.f_type != BPF_FS_MAGIC) {
    pr_warn("specified path %s is not on BPF FS\n", path);
    err = -EINVAL;
  }

  return err;
}

int bpf_program__pin(struct bpf_program *prog, const char *path)
{
  char *cp, errmsg[STRERR_BUFSIZE];
  int err;

  if (prog->fd < 0) {
    pr_warn("prog '%s': can't pin program that wasn't loaded\n", prog->name);
    return libbpf_err(-EINVAL);
  }

  err = make_parent_dir(path);
  if (err)
    return libbpf_err(err);

  err = check_path(path);
  if (err)
    return libbpf_err(err);

  if (bpf_obj_pin(prog->fd, path)) {
    err = -errno;
    cp = libbpf_strerror_r(err, errmsg, sizeof(errmsg));
    pr_warn("prog '%s': failed to pin at '%s': %s\n", prog->name, path, cp);
    return libbpf_err(err);
  }

  pr_debug("prog '%s': pinned at '%s'\n", prog->name, path);
  return 0;
}

int bpf_program__unpin(struct bpf_program *prog, const char *path)
{
  int err;

  if (prog->fd < 0) {
    pr_warn("prog '%s': can't unpin program that wasn't loaded\n", prog->name);
    return libbpf_err(-EINVAL);
  }

  err = check_path(path);
  if (err)
    return libbpf_err(err);

  err = unlink(path);
  if (err)
    return libbpf_err(-errno);

  pr_debug("prog '%s': unpinned from '%s'\n", prog->name, path);
  return 0;
}

int bpf_map__pin(struct bpf_map *map, const char *path)
{
  char *cp, errmsg[STRERR_BUFSIZE];
  int err;

  if (map == NULL) {
    pr_warn("invalid map pointer\n");
    return libbpf_err(-EINVAL);
  }

  if (map->pin_path) {
    if (path && strcmp(path, map->pin_path)) {
      pr_warn("map '%s' already has pin path '%s' different from '%s'\n",
        bpf_map__name(map), map->pin_path, path);
      return libbpf_err(-EINVAL);
    } else if (map->pinned) {
      pr_debug("map '%s' already pinned at '%s'; not re-pinning\n",
         bpf_map__name(map), map->pin_path);
      return 0;
    }
  } else {
    if (!path) {
      pr_warn("missing a path to pin map '%s' at\n",
        bpf_map__name(map));
      return libbpf_err(-EINVAL);
    } else if (map->pinned) {
      pr_warn("map '%s' already pinned\n", bpf_map__name(map));
      return libbpf_err(-EEXIST);
    }

    map->pin_path = strdup(path);
    if (!map->pin_path) {
      err = -errno;
      goto out_err;
    }
  }

  err = make_parent_dir(map->pin_path);
  if (err)
    return libbpf_err(err);

  err = check_path(map->pin_path);
  if (err)
    return libbpf_err(err);

  if (bpf_obj_pin(map->fd, map->pin_path)) {
    err = -errno;
    goto out_err;
  }

  map->pinned = true;
  pr_debug("pinned map '%s'\n", map->pin_path);

  return 0;

out_err:
  cp = libbpf_strerror_r(-err, errmsg, sizeof(errmsg));
  pr_warn("failed to pin map: %s\n", cp);
  return libbpf_err(err);
}

int bpf_map__unpin(struct bpf_map *map, const char *path)
{
  int err;

  if (map == NULL) {
    pr_warn("invalid map pointer\n");
    return libbpf_err(-EINVAL);
  }

  if (map->pin_path) {
    if (path && strcmp(path, map->pin_path)) {
      pr_warn("map '%s' already has pin path '%s' different from '%s'\n",
        bpf_map__name(map), map->pin_path, path);
      return libbpf_err(-EINVAL);
    }
    path = map->pin_path;
  } else if (!path) {
    pr_warn("no path to unpin map '%s' from\n",
      bpf_map__name(map));
    return libbpf_err(-EINVAL);
  }

  err = check_path(path);
  if (err)
    return libbpf_err(err);

  err = unlink(path);
  if (err != 0)
    return libbpf_err(-errno);

  map->pinned = false;
  pr_debug("unpinned map '%s' from '%s'\n", bpf_map__name(map), path);

  return 0;
}

int bpf_map__set_pin_path(struct bpf_map *map, const char *path)
{
  char *new = NULL;

  if (path) {
    new = strdup(path);
    if (!new)
      return libbpf_err(-errno);
  }

  free(map->pin_path);
  map->pin_path = new;
  return 0;
}

__alias(bpf_map__pin_path)
const char *bpf_map__get_pin_path(const struct bpf_map *map);

const char *bpf_map__pin_path(const struct bpf_map *map)
{
  return map->pin_path;
}

bool bpf_map__is_pinned(const struct bpf_map *map)
{
  return map->pinned;
}

static void sanitize_pin_path(char *s)
{
  /* bpffs disallows periods in path names */
  while (*s) {
    if (*s == '.')
      *s = '_';
    s++;
  }
}

int bpf_object__pin_maps(struct bpf_object *obj, const char *path)
{
  struct bpf_map *map;
  int err;

  if (!obj)
    return libbpf_err(-ENOENT);

  if (!obj->loaded) {
    pr_warn("object not yet loaded; load it first\n");
    return libbpf_err(-ENOENT);
  }

  bpf_object__for_each_map(map, obj) {
    char *pin_path = NULL;
    char buf[PATH_MAX];

    if (!map->autocreate)
      continue;

    if (path) {
      err = pathname_concat(buf, sizeof(buf), path, bpf_map__name(map));
      if (err)
        goto err_unpin_maps;
      sanitize_pin_path(buf);
      pin_path = buf;
    } else if (!map->pin_path) {
      continue;
    }

    err = bpf_map__pin(map, pin_path);
    if (err)
      goto err_unpin_maps;
  }

  return 0;

err_unpin_maps:
  while ((map = bpf_object__prev_map(obj, map))) {
    if (!map->pin_path)
      continue;

    bpf_map__unpin(map, NULL);
  }

  return libbpf_err(err);
}

int bpf_object__unpin_maps(struct bpf_object *obj, const char *path)
{
  struct bpf_map *map;
  int err;

  if (!obj)
    return libbpf_err(-ENOENT);

  bpf_object__for_each_map(map, obj) {
    char *pin_path = NULL;
    char buf[PATH_MAX];

    if (path) {
      err = pathname_concat(buf, sizeof(buf), path, bpf_map__name(map));
      if (err)
        return libbpf_err(err);
      sanitize_pin_path(buf);
      pin_path = buf;
    } else if (!map->pin_path) {
      continue;
    }

    err = bpf_map__unpin(map, pin_path);
    if (err)
      return libbpf_err(err);
  }

  return 0;
}

int bpf_object__pin_programs(struct bpf_object *obj, const char *path)
{
  struct bpf_program *prog;
  char buf[PATH_MAX];
  int err;

  if (!obj)
    return libbpf_err(-ENOENT);

  if (!obj->loaded) {
    pr_warn("object not yet loaded; load it first\n");
    return libbpf_err(-ENOENT);
  }

  bpf_object__for_each_program(prog, obj) {
    err = pathname_concat(buf, sizeof(buf), path, prog->name);
    if (err)
      goto err_unpin_programs;

    err = bpf_program__pin(prog, buf);
    if (err)
      goto err_unpin_programs;
  }

  return 0;

err_unpin_programs:
  while ((prog = bpf_object__prev_program(obj, prog))) {
    if (pathname_concat(buf, sizeof(buf), path, prog->name))
      continue;

    bpf_program__unpin(prog, buf);
  }

  return libbpf_err(err);
}

int bpf_object__unpin_programs(struct bpf_object *obj, const char *path)
{
  struct bpf_program *prog;
  int err;

  if (!obj)
    return libbpf_err(-ENOENT);

  bpf_object__for_each_program(prog, obj) {
    char buf[PATH_MAX];

    err = pathname_concat(buf, sizeof(buf), path, prog->name);
    if (err)
      return libbpf_err(err);

    err = bpf_program__unpin(prog, buf);
    if (err)
      return libbpf_err(err);
  }

  return 0;
}

int bpf_object__pin(struct bpf_object *obj, const char *path)
{
  int err;

  err = bpf_object__pin_maps(obj, path);
  if (err)
    return libbpf_err(err);

  err = bpf_object__pin_programs(obj, path);
  if (err) {
    bpf_object__unpin_maps(obj, path);
    return libbpf_err(err);
  }

  return 0;
}

int bpf_object__unpin(struct bpf_object *obj, const char *path)
{
  int err;

  err = bpf_object__unpin_programs(obj, path);
  if (err)
    return libbpf_err(err);

  err = bpf_object__unpin_maps(obj, path);
  if (err)
    return libbpf_err(err);

  return 0;
}

static void bpf_map__destroy(struct bpf_map *map)
{
  if (map->inner_map) {
    bpf_map__destroy(map->inner_map);
    zfree(&map->inner_map);
  }

  zfree(&map->init_slots);
  map->init_slots_sz = 0;

  if (map->mmaped) {
    size_t mmap_sz;

    mmap_sz = bpf_map_mmap_sz(map->def.value_size, map->def.max_entries);
    munmap(map->mmaped, mmap_sz);
    map->mmaped = NULL;
  }

  if (map->st_ops) {
    zfree(&map->st_ops->data);
    zfree(&map->st_ops->progs);
    zfree(&map->st_ops->kern_func_off);
    zfree(&map->st_ops);
  }

  zfree(&map->name);
  zfree(&map->real_name);
  zfree(&map->pin_path);

  if (map->fd >= 0)
    zclose(map->fd);
}

void bpf_object__close(struct bpf_object *obj)
{
  size_t i;

  if (IS_ERR_OR_NULL(obj))
    return;

  usdt_manager_free(obj->usdt_man);
  obj->usdt_man = NULL;

  bpf_gen__free(obj->gen_loader);
  bpf_object__elf_finish(obj);
  bpf_object_unload(obj);
  btf__free(obj->btf);
  btf__free(obj->btf_vmlinux);
  btf_ext__free(obj->btf_ext);

  for (i = 0; i < obj->nr_maps; i++)
    bpf_map__destroy(&obj->maps[i]);

  zfree(&obj->btf_custom_path);
  zfree(&obj->kconfig);

  for (i = 0; i < obj->nr_extern; i++)
    zfree(&obj->externs[i].essent_name);

  zfree(&obj->externs);
  obj->nr_extern = 0;

  zfree(&obj->maps);
  obj->nr_maps = 0;

  if (obj->programs && obj->nr_programs) {
    for (i = 0; i < obj->nr_programs; i++)
      bpf_program__exit(&obj->programs[i]);
  }
  zfree(&obj->programs);

  free(obj);
}

const char *bpf_object__name(const struct bpf_object *obj)
{
  return obj ? obj->name : libbpf_err_ptr(-EINVAL);
}

unsigned int bpf_object__kversion(const struct bpf_object *obj)
{
  return obj ? obj->kern_version : 0;
}

struct btf *bpf_object__btf(const struct bpf_object *obj)
{
  return obj ? obj->btf : NULL;
}

int bpf_object__btf_fd(const struct bpf_object *obj)
{
  return obj->btf ? btf__fd(obj->btf) : -1;
}

int bpf_object__set_kversion(struct bpf_object *obj, __u32 kern_version)
{
  if (obj->loaded)
    return libbpf_err(-EINVAL);

  obj->kern_version = kern_version;

  return 0;
}

int bpf_object__gen_loader(struct bpf_object *obj, struct gen_loader_opts *opts)
{
  struct bpf_gen *gen;

  if (!opts)
    return -EFAULT;
  if (!OPTS_VALID(opts, gen_loader_opts))
    return -EINVAL;
  gen = calloc(sizeof(*gen), 1);
  if (!gen)
    return -ENOMEM;
  gen->opts = opts;
  obj->gen_loader = gen;
  return 0;
}

static struct bpf_program *
__bpf_program__iter(const struct bpf_program *p, const struct bpf_object *obj,
        bool forward)
{
  size_t nr_programs = obj->nr_programs;
  ssize_t idx;

  if (!nr_programs)
    return NULL;

  if (!p)
    /* Iter from the beginning */
    return forward ? &obj->programs[0] :
      &obj->programs[nr_programs - 1];

  if (p->obj != obj) {
    pr_warn("error: program handler doesn't match object\n");
    return errno = EINVAL, NULL;
  }

  idx = (p - obj->programs) + (forward ? 1 : -1);
  if (idx >= obj->nr_programs || idx < 0)
    return NULL;
  return &obj->programs[idx];
}

struct bpf_program *
bpf_object__next_program(const struct bpf_object *obj, struct bpf_program *prev)
{
  struct bpf_program *prog = prev;

  do {
    prog = __bpf_program__iter(prog, obj, true);
  } while (prog && prog_is_subprog(obj, prog));

  return prog;
}

struct bpf_program *
bpf_object__prev_program(const struct bpf_object *obj, struct bpf_program *next)
{
  struct bpf_program *prog = next;

  do {
    prog = __bpf_program__iter(prog, obj, false);
  } while (prog && prog_is_subprog(obj, prog));

  return prog;
}

void bpf_program__set_ifindex(struct bpf_program *prog, __u32 ifindex)
{
  prog->prog_ifindex = ifindex;
}

const char *bpf_program__name(const struct bpf_program *prog)
{
  return prog->name;
}

const char *bpf_program__section_name(const struct bpf_program *prog)
{
  return prog->sec_name;
}

bool bpf_program__autoload(const struct bpf_program *prog)
{
  return prog->autoload;
}

int bpf_program__set_autoload(struct bpf_program *prog, bool autoload)
{
  if (prog->obj->loaded)
    return libbpf_err(-EINVAL);

  prog->autoload = autoload;
  return 0;
}

bool bpf_program__autoattach(const struct bpf_program *prog)
{
  return prog->autoattach;
}

void bpf_program__set_autoattach(struct bpf_program *prog, bool autoattach)
{
  prog->autoattach = autoattach;
}

const struct bpf_insn *bpf_program__insns(const struct bpf_program *prog)
{
  return prog->insns;
}

size_t bpf_program__insn_cnt(const struct bpf_program *prog)
{
  return prog->insns_cnt;
}

int bpf_program__set_insns(struct bpf_program *prog,
         struct bpf_insn *new_insns, size_t new_insn_cnt)
{
  struct bpf_insn *insns;

  if (prog->obj->loaded)
    return -EBUSY;

  insns = libbpf_reallocarray(prog->insns, new_insn_cnt, sizeof(*insns));
  /* NULL is a valid return from reallocarray if the new count is zero */
  if (!insns && new_insn_cnt) {
    pr_warn("prog '%s': failed to realloc prog code\n", prog->name);
    return -ENOMEM;
  }
  memcpy(insns, new_insns, new_insn_cnt * sizeof(*insns));

  prog->insns = insns;
  prog->insns_cnt = new_insn_cnt;
  return 0;
}

int bpf_program__fd(const struct bpf_program *prog)
{
  if (!prog)
    return libbpf_err(-EINVAL);

  if (prog->fd < 0)
    return libbpf_err(-ENOENT);

  return prog->fd;
}

__alias(bpf_program__type)
enum bpf_prog_type bpf_program__get_type(const struct bpf_program *prog);

enum bpf_prog_type bpf_program__type(const struct bpf_program *prog)
{
  return prog->type;
}

static size_t custom_sec_def_cnt;
static struct bpf_sec_def *custom_sec_defs;
static struct bpf_sec_def custom_fallback_def;
static bool has_custom_fallback_def;
static int last_custom_sec_def_handler_id;

int bpf_program__set_type(struct bpf_program *prog, enum bpf_prog_type type)
{
  if (prog->obj->loaded)
    return libbpf_err(-EBUSY);

  /* if type is not changed, do nothing */
  if (prog->type == type)
    return 0;

  prog->type = type;

  /* If a program type was changed, we need to reset associated SEC()
   * handler, as it will be invalid now. The only exception is a generic
   * fallback handler, which by definition is program type-agnostic and
   * is a catch-all custom handler, optionally set by the application,
   * so should be able to handle any type of BPF program.
   */
  if (prog->sec_def != &custom_fallback_def)
    prog->sec_def = NULL;
  return 0;
}

__alias(bpf_program__expected_attach_type)
enum bpf_attach_type bpf_program__get_expected_attach_type(const struct bpf_program *prog);

enum bpf_attach_type bpf_program__expected_attach_type(const struct bpf_program *prog)
{
  return prog->expected_attach_type;
}

int bpf_program__set_expected_attach_type(struct bpf_program *prog,
             enum bpf_attach_type type)
{
  if (prog->obj->loaded)
    return libbpf_err(-EBUSY);

  prog->expected_attach_type = type;
  return 0;
}

__u32 bpf_program__flags(const struct bpf_program *prog)
{
  return prog->prog_flags;
}

int bpf_program__set_flags(struct bpf_program *prog, __u32 flags)
{
  if (prog->obj->loaded)
    return libbpf_err(-EBUSY);

  prog->prog_flags = flags;
  return 0;
}

__u32 bpf_program__log_level(const struct bpf_program *prog)
{
  return prog->log_level;
}

int bpf_program__set_log_level(struct bpf_program *prog, __u32 log_level)
{
  if (prog->obj->loaded)
    return libbpf_err(-EBUSY);

  prog->log_level = log_level;
  return 0;
}

const char *bpf_program__log_buf(const struct bpf_program *prog, size_t *log_size)
{
  *log_size = prog->log_size;
  return prog->log_buf;
}

int bpf_program__set_log_buf(struct bpf_program *prog, char *log_buf, size_t log_size)
{
  if (log_size && !log_buf)
    return -EINVAL;
  if (prog->log_size > UINT_MAX)
    return -EINVAL;
  if (prog->obj->loaded)
    return -EBUSY;

  prog->log_buf = log_buf;
  prog->log_size = log_size;
  return 0;
}

#define SEC_DEF(sec_pfx, ptype, atype, flags, ...) {          \
  .sec = (char *)sec_pfx,               \
  .prog_type = BPF_PROG_TYPE_##ptype,           \
  .expected_attach_type = atype,              \
  .cookie = (long)(flags),              \
  .prog_prepare_load_fn = libbpf_prepare_prog_load,       \
  __VA_ARGS__                 \
}

static int attach_kprobe(const struct bpf_program *prog, long cookie, struct bpf_link **link);
static int attach_uprobe(const struct bpf_program *prog, long cookie, struct bpf_link **link);
static int attach_ksyscall(const struct bpf_program *prog, long cookie, struct bpf_link **link);
static int attach_usdt(const struct bpf_program *prog, long cookie, struct bpf_link **link);
static int attach_tp(const struct bpf_program *prog, long cookie, struct bpf_link **link);
static int attach_raw_tp(const struct bpf_program *prog, long cookie, struct bpf_link **link);
static int attach_trace(const struct bpf_program *prog, long cookie, struct bpf_link **link);
static int attach_kprobe_multi(const struct bpf_program *prog, long cookie, struct bpf_link **link);
static int attach_uprobe_multi(const struct bpf_program *prog, long cookie, struct bpf_link **link);
static int attach_lsm(const struct bpf_program *prog, long cookie, struct bpf_link **link);
static int attach_iter(const struct bpf_program *prog, long cookie, struct bpf_link **link);

static const struct bpf_sec_def section_defs[] = {
  SEC_DEF("socket",   SOCKET_FILTER, 0, SEC_NONE),
  SEC_DEF("sk_reuseport/migrate", SK_REUSEPORT, BPF_SK_REUSEPORT_SELECT_OR_MIGRATE, SEC_ATTACHABLE),
  SEC_DEF("sk_reuseport",   SK_REUSEPORT, BPF_SK_REUSEPORT_SELECT, SEC_ATTACHABLE),
  SEC_DEF("kprobe+",    KPROBE, 0, SEC_NONE, attach_kprobe),
  SEC_DEF("uprobe+",    KPROBE, 0, SEC_NONE, attach_uprobe),
  SEC_DEF("uprobe.s+",    KPROBE, 0, SEC_SLEEPABLE, attach_uprobe),
  SEC_DEF("kretprobe+",   KPROBE, 0, SEC_NONE, attach_kprobe),
  SEC_DEF("uretprobe+",   KPROBE, 0, SEC_NONE, attach_uprobe),
  SEC_DEF("uretprobe.s+",   KPROBE, 0, SEC_SLEEPABLE, attach_uprobe),
  SEC_DEF("kprobe.multi+",  KPROBE, BPF_TRACE_KPROBE_MULTI, SEC_NONE, attach_kprobe_multi),
  SEC_DEF("kretprobe.multi+", KPROBE, BPF_TRACE_KPROBE_MULTI, SEC_NONE, attach_kprobe_multi),
  SEC_DEF("uprobe.multi+",  KPROBE, BPF_TRACE_UPROBE_MULTI, SEC_NONE, attach_uprobe_multi),
  SEC_DEF("uretprobe.multi+", KPROBE, BPF_TRACE_UPROBE_MULTI, SEC_NONE, attach_uprobe_multi),
  SEC_DEF("uprobe.multi.s+",  KPROBE, BPF_TRACE_UPROBE_MULTI, SEC_SLEEPABLE, attach_uprobe_multi),
  SEC_DEF("uretprobe.multi.s+", KPROBE, BPF_TRACE_UPROBE_MULTI, SEC_SLEEPABLE, attach_uprobe_multi),
  SEC_DEF("ksyscall+",    KPROBE, 0, SEC_NONE, attach_ksyscall),
  SEC_DEF("kretsyscall+",   KPROBE, 0, SEC_NONE, attach_ksyscall),
  SEC_DEF("usdt+",    KPROBE, 0, SEC_USDT, attach_usdt),
  SEC_DEF("usdt.s+",    KPROBE, 0, SEC_USDT | SEC_SLEEPABLE, attach_usdt),
  SEC_DEF("tc/ingress",   SCHED_CLS, BPF_TCX_INGRESS, SEC_NONE), /* alias for tcx */
  SEC_DEF("tc/egress",    SCHED_CLS, BPF_TCX_EGRESS, SEC_NONE),  /* alias for tcx */
  SEC_DEF("tcx/ingress",    SCHED_CLS, BPF_TCX_INGRESS, SEC_NONE),
  SEC_DEF("tcx/egress",   SCHED_CLS, BPF_TCX_EGRESS, SEC_NONE),
  SEC_DEF("tc",     SCHED_CLS, 0, SEC_NONE), /* deprecated / legacy, use tcx */
  SEC_DEF("classifier",   SCHED_CLS, 0, SEC_NONE), /* deprecated / legacy, use tcx */
  SEC_DEF("action",   SCHED_ACT, 0, SEC_NONE), /* deprecated / legacy, use tcx */
  SEC_DEF("netkit/primary", SCHED_CLS, BPF_NETKIT_PRIMARY, SEC_NONE),
  SEC_DEF("netkit/peer",    SCHED_CLS, BPF_NETKIT_PEER, SEC_NONE),
  SEC_DEF("tracepoint+",    TRACEPOINT, 0, SEC_NONE, attach_tp),
  SEC_DEF("tp+",      TRACEPOINT, 0, SEC_NONE, attach_tp),
  SEC_DEF("raw_tracepoint+",  RAW_TRACEPOINT, 0, SEC_NONE, attach_raw_tp),
  SEC_DEF("raw_tp+",    RAW_TRACEPOINT, 0, SEC_NONE, attach_raw_tp),
  SEC_DEF("raw_tracepoint.w+",  RAW_TRACEPOINT_WRITABLE, 0, SEC_NONE, attach_raw_tp),
  SEC_DEF("raw_tp.w+",    RAW_TRACEPOINT_WRITABLE, 0, SEC_NONE, attach_raw_tp),
  SEC_DEF("tp_btf+",    TRACING, BPF_TRACE_RAW_TP, SEC_ATTACH_BTF, attach_trace),
  SEC_DEF("fentry+",    TRACING, BPF_TRACE_FENTRY, SEC_ATTACH_BTF, attach_trace),
  SEC_DEF("fmod_ret+",    TRACING, BPF_MODIFY_RETURN, SEC_ATTACH_BTF, attach_trace),
  SEC_DEF("fexit+",   TRACING, BPF_TRACE_FEXIT, SEC_ATTACH_BTF, attach_trace),
  SEC_DEF("fentry.s+",    TRACING, BPF_TRACE_FENTRY, SEC_ATTACH_BTF | SEC_SLEEPABLE, attach_trace),
  SEC_DEF("fmod_ret.s+",    TRACING, BPF_MODIFY_RETURN, SEC_ATTACH_BTF | SEC_SLEEPABLE, attach_trace),
  SEC_DEF("fexit.s+",   TRACING, BPF_TRACE_FEXIT, SEC_ATTACH_BTF | SEC_SLEEPABLE, attach_trace),
  SEC_DEF("freplace+",    EXT, 0, SEC_ATTACH_BTF, attach_trace),
  SEC_DEF("lsm+",     LSM, BPF_LSM_MAC, SEC_ATTACH_BTF, attach_lsm),
  SEC_DEF("lsm.s+",   LSM, BPF_LSM_MAC, SEC_ATTACH_BTF | SEC_SLEEPABLE, attach_lsm),
  SEC_DEF("lsm_cgroup+",    LSM, BPF_LSM_CGROUP, SEC_ATTACH_BTF),
  SEC_DEF("iter+",    TRACING, BPF_TRACE_ITER, SEC_ATTACH_BTF, attach_iter),
  SEC_DEF("iter.s+",    TRACING, BPF_TRACE_ITER, SEC_ATTACH_BTF | SEC_SLEEPABLE, attach_iter),
  SEC_DEF("syscall",    SYSCALL, 0, SEC_SLEEPABLE),
  SEC_DEF("xdp.frags/devmap", XDP, BPF_XDP_DEVMAP, SEC_XDP_FRAGS),
  SEC_DEF("xdp/devmap",   XDP, BPF_XDP_DEVMAP, SEC_ATTACHABLE),
  SEC_DEF("xdp.frags/cpumap", XDP, BPF_XDP_CPUMAP, SEC_XDP_FRAGS),
  SEC_DEF("xdp/cpumap",   XDP, BPF_XDP_CPUMAP, SEC_ATTACHABLE),
  SEC_DEF("xdp.frags",    XDP, BPF_XDP, SEC_XDP_FRAGS),
  SEC_DEF("xdp",      XDP, BPF_XDP, SEC_ATTACHABLE_OPT),
  SEC_DEF("perf_event",   PERF_EVENT, 0, SEC_NONE),
  SEC_DEF("lwt_in",   LWT_IN, 0, SEC_NONE),
  SEC_DEF("lwt_out",    LWT_OUT, 0, SEC_NONE),
  SEC_DEF("lwt_xmit",   LWT_XMIT, 0, SEC_NONE),
  SEC_DEF("lwt_seg6local",  LWT_SEG6LOCAL, 0, SEC_NONE),
  SEC_DEF("sockops",    SOCK_OPS, BPF_CGROUP_SOCK_OPS, SEC_ATTACHABLE_OPT),
  SEC_DEF("sk_skb/stream_parser", SK_SKB, BPF_SK_SKB_STREAM_PARSER, SEC_ATTACHABLE_OPT),
  SEC_DEF("sk_skb/stream_verdict",SK_SKB, BPF_SK_SKB_STREAM_VERDICT, SEC_ATTACHABLE_OPT),
  SEC_DEF("sk_skb",   SK_SKB, 0, SEC_NONE),
  SEC_DEF("sk_msg",   SK_MSG, BPF_SK_MSG_VERDICT, SEC_ATTACHABLE_OPT),
  SEC_DEF("lirc_mode2",   LIRC_MODE2, BPF_LIRC_MODE2, SEC_ATTACHABLE_OPT),
  SEC_DEF("flow_dissector", FLOW_DISSECTOR, BPF_FLOW_DISSECTOR, SEC_ATTACHABLE_OPT),
  SEC_DEF("cgroup_skb/ingress", CGROUP_SKB, BPF_CGROUP_INET_INGRESS, SEC_ATTACHABLE_OPT),
  SEC_DEF("cgroup_skb/egress",  CGROUP_SKB, BPF_CGROUP_INET_EGRESS, SEC_ATTACHABLE_OPT),
  SEC_DEF("cgroup/skb",   CGROUP_SKB, 0, SEC_NONE),
  SEC_DEF("cgroup/sock_create", CGROUP_SOCK, BPF_CGROUP_INET_SOCK_CREATE, SEC_ATTACHABLE),
  SEC_DEF("cgroup/sock_release",  CGROUP_SOCK, BPF_CGROUP_INET_SOCK_RELEASE, SEC_ATTACHABLE),
  SEC_DEF("cgroup/sock",    CGROUP_SOCK, BPF_CGROUP_INET_SOCK_CREATE, SEC_ATTACHABLE_OPT),
  SEC_DEF("cgroup/post_bind4",  CGROUP_SOCK, BPF_CGROUP_INET4_POST_BIND, SEC_ATTACHABLE),
  SEC_DEF("cgroup/post_bind6",  CGROUP_SOCK, BPF_CGROUP_INET6_POST_BIND, SEC_ATTACHABLE),
  SEC_DEF("cgroup/bind4",   CGROUP_SOCK_ADDR, BPF_CGROUP_INET4_BIND, SEC_ATTACHABLE),
  SEC_DEF("cgroup/bind6",   CGROUP_SOCK_ADDR, BPF_CGROUP_INET6_BIND, SEC_ATTACHABLE),
  SEC_DEF("cgroup/connect4",  CGROUP_SOCK_ADDR, BPF_CGROUP_INET4_CONNECT, SEC_ATTACHABLE),
  SEC_DEF("cgroup/connect6",  CGROUP_SOCK_ADDR, BPF_CGROUP_INET6_CONNECT, SEC_ATTACHABLE),
  SEC_DEF("cgroup/connect_unix",  CGROUP_SOCK_ADDR, BPF_CGROUP_UNIX_CONNECT, SEC_ATTACHABLE),
  SEC_DEF("cgroup/sendmsg4",  CGROUP_SOCK_ADDR, BPF_CGROUP_UDP4_SENDMSG, SEC_ATTACHABLE),
  SEC_DEF("cgroup/sendmsg6",  CGROUP_SOCK_ADDR, BPF_CGROUP_UDP6_SENDMSG, SEC_ATTACHABLE),
  SEC_DEF("cgroup/sendmsg_unix",  CGROUP_SOCK_ADDR, BPF_CGROUP_UNIX_SENDMSG, SEC_ATTACHABLE),
  SEC_DEF("cgroup/recvmsg4",  CGROUP_SOCK_ADDR, BPF_CGROUP_UDP4_RECVMSG, SEC_ATTACHABLE),
  SEC_DEF("cgroup/recvmsg6",  CGROUP_SOCK_ADDR, BPF_CGROUP_UDP6_RECVMSG, SEC_ATTACHABLE),
  SEC_DEF("cgroup/recvmsg_unix",  CGROUP_SOCK_ADDR, BPF_CGROUP_UNIX_RECVMSG, SEC_ATTACHABLE),
  SEC_DEF("cgroup/getpeername4",  CGROUP_SOCK_ADDR, BPF_CGROUP_INET4_GETPEERNAME, SEC_ATTACHABLE),
  SEC_DEF("cgroup/getpeername6",  CGROUP_SOCK_ADDR, BPF_CGROUP_INET6_GETPEERNAME, SEC_ATTACHABLE),
  SEC_DEF("cgroup/getpeername_unix", CGROUP_SOCK_ADDR, BPF_CGROUP_UNIX_GETPEERNAME, SEC_ATTACHABLE),
  SEC_DEF("cgroup/getsockname4",  CGROUP_SOCK_ADDR, BPF_CGROUP_INET4_GETSOCKNAME, SEC_ATTACHABLE),
  SEC_DEF("cgroup/getsockname6",  CGROUP_SOCK_ADDR, BPF_CGROUP_INET6_GETSOCKNAME, SEC_ATTACHABLE),
  SEC_DEF("cgroup/getsockname_unix", CGROUP_SOCK_ADDR, BPF_CGROUP_UNIX_GETSOCKNAME, SEC_ATTACHABLE),
  SEC_DEF("cgroup/sysctl",  CGROUP_SYSCTL, BPF_CGROUP_SYSCTL, SEC_ATTACHABLE),
  SEC_DEF("cgroup/getsockopt",  CGROUP_SOCKOPT, BPF_CGROUP_GETSOCKOPT, SEC_ATTACHABLE),
  SEC_DEF("cgroup/setsockopt",  CGROUP_SOCKOPT, BPF_CGROUP_SETSOCKOPT, SEC_ATTACHABLE),
  SEC_DEF("cgroup/dev",   CGROUP_DEVICE, BPF_CGROUP_DEVICE, SEC_ATTACHABLE_OPT),
  SEC_DEF("struct_ops+",    STRUCT_OPS, 0, SEC_NONE),
  SEC_DEF("struct_ops.s+",  STRUCT_OPS, 0, SEC_SLEEPABLE),
  SEC_DEF("sk_lookup",    SK_LOOKUP, BPF_SK_LOOKUP, SEC_ATTACHABLE),
  SEC_DEF("netfilter",    NETFILTER, BPF_NETFILTER, SEC_NONE),
};

int libbpf_register_prog_handler(const char *sec,
         enum bpf_prog_type prog_type,
         enum bpf_attach_type exp_attach_type,
         const struct libbpf_prog_handler_opts *opts)
{
  struct bpf_sec_def *sec_def;

  if (!OPTS_VALID(opts, libbpf_prog_handler_opts))
    return libbpf_err(-EINVAL);

  if (last_custom_sec_def_handler_id == INT_MAX) /* prevent overflow */
    return libbpf_err(-E2BIG);

  if (sec) {
    sec_def = libbpf_reallocarray(custom_sec_defs, custom_sec_def_cnt + 1,
                sizeof(*sec_def));
    if (!sec_def)
      return libbpf_err(-ENOMEM);

    custom_sec_defs = sec_def;
    sec_def = &custom_sec_defs[custom_sec_def_cnt];
  } else {
    if (has_custom_fallback_def)
      return libbpf_err(-EBUSY);

    sec_def = &custom_fallback_def;
  }

  sec_def->sec = sec ? strdup(sec) : NULL;
  if (sec && !sec_def->sec)
    return libbpf_err(-ENOMEM);

  sec_def->prog_type = prog_type;
  sec_def->expected_attach_type = exp_attach_type;
  sec_def->cookie = OPTS_GET(opts, cookie, 0);

  sec_def->prog_setup_fn = OPTS_GET(opts, prog_setup_fn, NULL);
  sec_def->prog_prepare_load_fn = OPTS_GET(opts, prog_prepare_load_fn, NULL);
  sec_def->prog_attach_fn = OPTS_GET(opts, prog_attach_fn, NULL);

  sec_def->handler_id = ++last_custom_sec_def_handler_id;

  if (sec)
    custom_sec_def_cnt++;
  else
    has_custom_fallback_def = true;

  return sec_def->handler_id;
}

int libbpf_unregister_prog_handler(int handler_id)
{
  struct bpf_sec_def *sec_defs;
  int i;

  if (handler_id <= 0)
    return libbpf_err(-EINVAL);

  if (has_custom_fallback_def && custom_fallback_def.handler_id == handler_id) {
    memset(&custom_fallback_def, 0, sizeof(custom_fallback_def));
    has_custom_fallback_def = false;
    return 0;
  }

  for (i = 0; i < custom_sec_def_cnt; i++) {
    if (custom_sec_defs[i].handler_id == handler_id)
      break;
  }

  if (i == custom_sec_def_cnt)
    return libbpf_err(-ENOENT);

  free(custom_sec_defs[i].sec);
  for (i = i + 1; i < custom_sec_def_cnt; i++)
    custom_sec_defs[i - 1] = custom_sec_defs[i];
  custom_sec_def_cnt--;

  /* try to shrink the array, but it's ok if we couldn't */
  sec_defs = libbpf_reallocarray(custom_sec_defs, custom_sec_def_cnt, sizeof(*sec_defs));
  /* if new count is zero, reallocarray can return a valid NULL result;
   * in this case the previous pointer will be freed, so we *have to*
   * reassign old pointer to the new value (even if it's NULL)
   */
  if (sec_defs || custom_sec_def_cnt == 0)
    custom_sec_defs = sec_defs;

  return 0;
}

static bool sec_def_matches(const struct bpf_sec_def *sec_def, const char *sec_name)
{
  size_t len = strlen(sec_def->sec);

  /* "type/" always has to have proper SEC("type/extras") form */
  if (sec_def->sec[len - 1] == '/') {
    if (str_has_pfx(sec_name, sec_def->sec))
      return true;
    return false;
  }

  /* "type+" means it can be either exact SEC("type") or
   * well-formed SEC("type/extras") with proper '/' separator
   */
  if (sec_def->sec[len - 1] == '+') {
    len--;
    /* not even a prefix */
    if (strncmp(sec_name, sec_def->sec, len) != 0)
      return false;
    /* exact match or has '/' separator */
    if (sec_name[len] == '\0' || sec_name[len] == '/')
      return true;
    return false;
  }

  return strcmp(sec_name, sec_def->sec) == 0;
}

static const struct bpf_sec_def *find_sec_def(const char *sec_name)
{
  const struct bpf_sec_def *sec_def;
  int i, n;

  n = custom_sec_def_cnt;
  for (i = 0; i < n; i++) {
    sec_def = &custom_sec_defs[i];
    if (sec_def_matches(sec_def, sec_name))
      return sec_def;
  }

  n = ARRAY_SIZE(section_defs);
  for (i = 0; i < n; i++) {
    sec_def = &section_defs[i];
    if (sec_def_matches(sec_def, sec_name))
      return sec_def;
  }

  if (has_custom_fallback_def)
    return &custom_fallback_def;

  return NULL;
}

#define MAX_TYPE_NAME_SIZE 32

static char *libbpf_get_type_names(bool attach_type)
{
  int i, len = ARRAY_SIZE(section_defs) * MAX_TYPE_NAME_SIZE;
  char *buf;

  buf = malloc(len);
  if (!buf)
    return NULL;

  buf[0] = '\0';
  /* Forge string buf with all available names */
  for (i = 0; i < ARRAY_SIZE(section_defs); i++) {
    const struct bpf_sec_def *sec_def = &section_defs[i];

    if (attach_type) {
      if (sec_def->prog_prepare_load_fn != libbpf_prepare_prog_load)
        continue;

      if (!(sec_def->cookie & SEC_ATTACHABLE))
        continue;
    }

    if (strlen(buf) + strlen(section_defs[i].sec) + 2 > len) {
      free(buf);
      return NULL;
    }
    strcat(buf, " ");
    strcat(buf, section_defs[i].sec);
  }

  return buf;
}

int libbpf_prog_type_by_name(const char *name, enum bpf_prog_type *prog_type,
           enum bpf_attach_type *expected_attach_type)
{
  const struct bpf_sec_def *sec_def;
  char *type_names;

  if (!name)
    return libbpf_err(-EINVAL);

  sec_def = find_sec_def(name);
  if (sec_def) {
    *prog_type = sec_def->prog_type;
    *expected_attach_type = sec_def->expected_attach_type;
    return 0;
  }

  pr_debug("failed to guess program type from ELF section '%s'\n", name);
  type_names = libbpf_get_type_names(false);
  if (type_names != NULL) {
    pr_debug("supported section(type) names are:%s\n", type_names);
    free(type_names);
  }

  return libbpf_err(-ESRCH);
}

const char *libbpf_bpf_attach_type_str(enum bpf_attach_type t)
{
  if (t < 0 || t >= ARRAY_SIZE(attach_type_name))
    return NULL;

  return attach_type_name[t];
}

const char *libbpf_bpf_link_type_str(enum bpf_link_type t)
{
  if (t < 0 || t >= ARRAY_SIZE(link_type_name))
    return NULL;

  return link_type_name[t];
}

const char *libbpf_bpf_map_type_str(enum bpf_map_type t)
{
  if (t < 0 || t >= ARRAY_SIZE(map_type_name))
    return NULL;

  return map_type_name[t];
}

const char *libbpf_bpf_prog_type_str(enum bpf_prog_type t)
{
  if (t < 0 || t >= ARRAY_SIZE(prog_type_name))
    return NULL;

  return prog_type_name[t];
}

static struct bpf_map *find_struct_ops_map_by_offset(struct bpf_object *obj,
                 int sec_idx,
                 size_t offset)
{
  struct bpf_map *map;
  size_t i;

  for (i = 0; i < obj->nr_maps; i++) {
    map = &obj->maps[i];
    if (!bpf_map__is_struct_ops(map))
      continue;
    if (map->sec_idx == sec_idx &&
        map->sec_offset <= offset &&
        offset - map->sec_offset < map->def.value_size)
      return map;
  }

  return NULL;
}

/* Collect the reloc from ELF and populate the st_ops->progs[] */
static int bpf_object__collect_st_ops_relos(struct bpf_object *obj,
              Elf64_Shdr *shdr, Elf_Data *data)
{
  const struct btf_member *member;
  struct bpf_struct_ops *st_ops;
  struct bpf_program *prog;
  unsigned int shdr_idx;
  const struct btf *btf;
  struct bpf_map *map;
  unsigned int moff, insn_idx;
  const char *name;
  __u32 member_idx;
  Elf64_Sym *sym;
  Elf64_Rel *rel;
  int i, nrels;

  btf = obj->btf;
  nrels = shdr->sh_size / shdr->sh_entsize;
  for (i = 0; i < nrels; i++) {
    rel = elf_rel_by_idx(data, i);
    if (!rel) {
      pr_warn("struct_ops reloc: failed to get %d reloc\n", i);
      return -LIBBPF_ERRNO__FORMAT;
    }

    sym = elf_sym_by_idx(obj, ELF64_R_SYM(rel->r_info));
    if (!sym) {
      pr_warn("struct_ops reloc: symbol %zx not found\n",
        (size_t)ELF64_R_SYM(rel->r_info));
      return -LIBBPF_ERRNO__FORMAT;
    }

    name = elf_sym_str(obj, sym->st_name) ?: "<?>";
    map = find_struct_ops_map_by_offset(obj, shdr->sh_info, rel->r_offset);
    if (!map) {
      pr_warn("struct_ops reloc: cannot find map at rel->r_offset %zu\n",
        (size_t)rel->r_offset);
      return -EINVAL;
    }

    moff = rel->r_offset - map->sec_offset;
    shdr_idx = sym->st_shndx;
    st_ops = map->st_ops;
    pr_debug("struct_ops reloc %s: for %lld value %lld shdr_idx %u rel->r_offset %zu map->sec_offset %zu name %d (\'%s\')\n",
       map->name,
       (long long)(rel->r_info >> 32),
       (long long)sym->st_value,
       shdr_idx, (size_t)rel->r_offset,
       map->sec_offset, sym->st_name, name);

    if (shdr_idx >= SHN_LORESERVE) {
      pr_warn("struct_ops reloc %s: rel->r_offset %zu shdr_idx %u unsupported non-static function\n",
        map->name, (size_t)rel->r_offset, shdr_idx);
      return -LIBBPF_ERRNO__RELOC;
    }
    if (sym->st_value % BPF_INSN_SZ) {
      pr_warn("struct_ops reloc %s: invalid target program offset %llu\n",
        map->name, (unsigned long long)sym->st_value);
      return -LIBBPF_ERRNO__FORMAT;
    }
    insn_idx = sym->st_value / BPF_INSN_SZ;

    member = find_member_by_offset(st_ops->type, moff * 8);
    if (!member) {
      pr_warn("struct_ops reloc %s: cannot find member at moff %u\n",
        map->name, moff);
      return -EINVAL;
    }
    member_idx = member - btf_members(st_ops->type);
    name = btf__name_by_offset(btf, member->name_off);

    if (!resolve_func_ptr(btf, member->type, NULL)) {
      pr_warn("struct_ops reloc %s: cannot relocate non func ptr %s\n",
        map->name, name);
      return -EINVAL;
    }

    prog = find_prog_by_sec_insn(obj, shdr_idx, insn_idx);
    if (!prog) {
      pr_warn("struct_ops reloc %s: cannot find prog at shdr_idx %u to relocate func ptr %s\n",
        map->name, shdr_idx, name);
      return -EINVAL;
    }

    /* prevent the use of BPF prog with invalid type */
    if (prog->type != BPF_PROG_TYPE_STRUCT_OPS) {
      pr_warn("struct_ops reloc %s: prog %s is not struct_ops BPF program\n",
        map->name, prog->name);
      return -EINVAL;
    }

    /* if we haven't yet processed this BPF program, record proper
     * attach_btf_id and member_idx
     */
    if (!prog->attach_btf_id) {
      prog->attach_btf_id = st_ops->type_id;
      prog->expected_attach_type = member_idx;
    }

    /* struct_ops BPF prog can be re-used between multiple
     * .struct_ops & .struct_ops.link as long as it's the
     * same struct_ops struct definition and the same
     * function pointer field
     */
    if (prog->attach_btf_id != st_ops->type_id ||
        prog->expected_attach_type != member_idx) {
      pr_warn("struct_ops reloc %s: cannot use prog %s in sec %s with type %u attach_btf_id %u expected_attach_type %u for func ptr %s\n",
        map->name, prog->name, prog->sec_name, prog->type,
        prog->attach_btf_id, prog->expected_attach_type, name);
      return -EINVAL;
    }

    st_ops->progs[member_idx] = prog;
  }

  return 0;
}

#define BTF_TRACE_PREFIX "btf_trace_"
#define BTF_LSM_PREFIX "bpf_lsm_"
#define BTF_ITER_PREFIX "bpf_iter_"
#define BTF_MAX_NAME_SIZE 128

void btf_get_kernel_prefix_kind(enum bpf_attach_type attach_type,
        const char **prefix, int *kind)
{
  switch (attach_type) {
  case BPF_TRACE_RAW_TP:
    *prefix = BTF_TRACE_PREFIX;
    *kind = BTF_KIND_TYPEDEF;
    break;
  case BPF_LSM_MAC:
  case BPF_LSM_CGROUP:
    *prefix = BTF_LSM_PREFIX;
    *kind = BTF_KIND_FUNC;
    break;
  case BPF_TRACE_ITER:
    *prefix = BTF_ITER_PREFIX;
    *kind = BTF_KIND_FUNC;
    break;
  default:
    *prefix = "";
    *kind = BTF_KIND_FUNC;
  }
}

static int find_btf_by_prefix_kind(const struct btf *btf, const char *prefix,
           const char *name, __u32 kind)
{
  char btf_type_name[BTF_MAX_NAME_SIZE];
  int ret;

  ret = snprintf(btf_type_name, sizeof(btf_type_name),
           "%s%s", prefix, name);
  /* snprintf returns the number of characters written excluding the
   * terminating null. So, if >= BTF_MAX_NAME_SIZE are written, it
   * indicates truncation.
   */
  if (ret < 0 || ret >= sizeof(btf_type_name))
    return -ENAMETOOLONG;
  return btf__find_by_name_kind(btf, btf_type_name, kind);
}

static inline int find_attach_btf_id(struct btf *btf, const char *name,
             enum bpf_attach_type attach_type)
{
  const char *prefix;
  int kind;

  btf_get_kernel_prefix_kind(attach_type, &prefix, &kind);
  return find_btf_by_prefix_kind(btf, prefix, name, kind);
}

int libbpf_find_vmlinux_btf_id(const char *name,
             enum bpf_attach_type attach_type)
{
  struct btf *btf;
  int err;

  btf = btf__load_vmlinux_btf();
  err = libbpf_get_error(btf);
  if (err) {
    pr_warn("vmlinux BTF is not found\n");
    return libbpf_err(err);
  }

  err = find_attach_btf_id(btf, name, attach_type);
  if (err <= 0)
    pr_warn("%s is not found in vmlinux BTF\n", name);

  btf__free(btf);
  return libbpf_err(err);
}

static int libbpf_find_prog_btf_id(const char *name, __u32 attach_prog_fd)
{
  struct bpf_prog_info info;
  __u32 info_len = sizeof(info);
  struct btf *btf;
  int err;

  memset(&info, 0, info_len);
  err = bpf_prog_get_info_by_fd(attach_prog_fd, &info, &info_len);
  if (err) {
    pr_warn("failed bpf_prog_get_info_by_fd for FD %d: %d\n",
      attach_prog_fd, err);
    return err;
  }

  err = -EINVAL;
  if (!info.btf_id) {
    pr_warn("The target program doesn't have BTF\n");
    goto out;
  }
  btf = btf__load_from_kernel_by_id(info.btf_id);
  err = libbpf_get_error(btf);
  if (err) {
    pr_warn("Failed to get BTF %d of the program: %d\n", info.btf_id, err);
    goto out;
  }
  err = btf__find_by_name_kind(btf, name, BTF_KIND_FUNC);
  btf__free(btf);
  if (err <= 0) {
    pr_warn("%s is not found in prog's BTF\n", name);
    goto out;
  }
out:
  return err;
}

static int find_kernel_btf_id(struct bpf_object *obj, const char *attach_name,
            enum bpf_attach_type attach_type,
            int *btf_obj_fd, int *btf_type_id)
{
  int ret, i;

  ret = find_attach_btf_id(obj->btf_vmlinux, attach_name, attach_type);
  if (ret > 0) {
    *btf_obj_fd = 0; /* vmlinux BTF */
    *btf_type_id = ret;
    return 0;
  }
  if (ret != -ENOENT)
    return ret;

  ret = load_module_btfs(obj);
  if (ret)
    return ret;

  for (i = 0; i < obj->btf_module_cnt; i++) {
    const struct module_btf *mod = &obj->btf_modules[i];

    ret = find_attach_btf_id(mod->btf, attach_name, attach_type);
    if (ret > 0) {
      *btf_obj_fd = mod->fd;
      *btf_type_id = ret;
      return 0;
    }
    if (ret == -ENOENT)
      continue;

    return ret;
  }

  return -ESRCH;
}

static int libbpf_find_attach_btf_id(struct bpf_program *prog, const char *attach_name,
             int *btf_obj_fd, int *btf_type_id)
{
  enum bpf_attach_type attach_type = prog->expected_attach_type;
  __u32 attach_prog_fd = prog->attach_prog_fd;
  int err = 0;

  /* BPF program's BTF ID */
  if (prog->type == BPF_PROG_TYPE_EXT || attach_prog_fd) {
    if (!attach_prog_fd) {
      pr_warn("prog '%s': attach program FD is not set\n", prog->name);
      return -EINVAL;
    }
    err = libbpf_find_prog_btf_id(attach_name, attach_prog_fd);
    if (err < 0) {
      pr_warn("prog '%s': failed to find BPF program (FD %d) BTF ID for '%s': %d\n",
         prog->name, attach_prog_fd, attach_name, err);
      return err;
    }
    *btf_obj_fd = 0;
    *btf_type_id = err;
    return 0;
  }

  /* kernel/module BTF ID */
  if (prog->obj->gen_loader) {
    bpf_gen__record_attach_target(prog->obj->gen_loader, attach_name, attach_type);
    *btf_obj_fd = 0;
    *btf_type_id = 1;
  } else {
    err = find_kernel_btf_id(prog->obj, attach_name, attach_type, btf_obj_fd, btf_type_id);
  }
  if (err) {
    pr_warn("prog '%s': failed to find kernel BTF type ID of '%s': %d\n",
      prog->name, attach_name, err);
    return err;
  }
  return 0;
}

int libbpf_attach_type_by_name(const char *name,
             enum bpf_attach_type *attach_type)
{
  char *type_names;
  const struct bpf_sec_def *sec_def;

  if (!name)
    return libbpf_err(-EINVAL);

  sec_def = find_sec_def(name);
  if (!sec_def) {
    pr_debug("failed to guess attach type based on ELF section name '%s'\n", name);
    type_names = libbpf_get_type_names(true);
    if (type_names != NULL) {
      pr_debug("attachable section(type) names are:%s\n", type_names);
      free(type_names);
    }

    return libbpf_err(-EINVAL);
  }

  if (sec_def->prog_prepare_load_fn != libbpf_prepare_prog_load)
    return libbpf_err(-EINVAL);
  if (!(sec_def->cookie & SEC_ATTACHABLE))
    return libbpf_err(-EINVAL);

  *attach_type = sec_def->expected_attach_type;
  return 0;
}

int bpf_map__fd(const struct bpf_map *map)
{
  return map ? map->fd : libbpf_err(-EINVAL);
}

static bool map_uses_real_name(const struct bpf_map *map)
{
  /* Since libbpf started to support custom .data.* and .rodata.* maps,
   * their user-visible name differs from kernel-visible name. Users see
   * such map's corresponding ELF section name as a map name.
   * This check distinguishes .data/.rodata from .data.* and .rodata.*
   * maps to know which name has to be returned to the user.
   */
  if (map->libbpf_type == LIBBPF_MAP_DATA && strcmp(map->real_name, DATA_SEC) != 0)
    return true;
  if (map->libbpf_type == LIBBPF_MAP_RODATA && strcmp(map->real_name, RODATA_SEC) != 0)
    return true;
  return false;
}

const char *bpf_map__name(const struct bpf_map *map)
{
  if (!map)
    return NULL;

  if (map_uses_real_name(map))
    return map->real_name;

  return map->name;
}

enum bpf_map_type bpf_map__type(const struct bpf_map *map)
{
  return map->def.type;
}

int bpf_map__set_type(struct bpf_map *map, enum bpf_map_type type)
{
  if (map->fd >= 0)
    return libbpf_err(-EBUSY);
  map->def.type = type;
  return 0;
}

__u32 bpf_map__map_flags(const struct bpf_map *map)
{
  return map->def.map_flags;
}

int bpf_map__set_map_flags(struct bpf_map *map, __u32 flags)
{
  if (map->fd >= 0)
    return libbpf_err(-EBUSY);
  map->def.map_flags = flags;
  return 0;
}

__u64 bpf_map__map_extra(const struct bpf_map *map)
{
  return map->map_extra;
}

int bpf_map__set_map_extra(struct bpf_map *map, __u64 map_extra)
{
  if (map->fd >= 0)
    return libbpf_err(-EBUSY);
  map->map_extra = map_extra;
  return 0;
}

__u32 bpf_map__numa_node(const struct bpf_map *map)
{
  return map->numa_node;
}

int bpf_map__set_numa_node(struct bpf_map *map, __u32 numa_node)
{
  if (map->fd >= 0)
    return libbpf_err(-EBUSY);
  map->numa_node = numa_node;
  return 0;
}

__u32 bpf_map__key_size(const struct bpf_map *map)
{
  return map->def.key_size;
}

int bpf_map__set_key_size(struct bpf_map *map, __u32 size)
{
  if (map->fd >= 0)
    return libbpf_err(-EBUSY);
  map->def.key_size = size;
  return 0;
}

__u32 bpf_map__value_size(const struct bpf_map *map)
{
  return map->def.value_size;
}

static int map_btf_datasec_resize(struct bpf_map *map, __u32 size)
{
  struct btf *btf;
  struct btf_type *datasec_type, *var_type;
  struct btf_var_secinfo *var;
  const struct btf_type *array_type;
  const struct btf_array *array;
  int vlen, element_sz, new_array_id;
  __u32 nr_elements;

  /* check btf existence */
  btf = bpf_object__btf(map->obj);
  if (!btf)
    return -ENOENT;

  /* verify map is datasec */
  datasec_type = btf_type_by_id(btf, bpf_map__btf_value_type_id(map));
  if (!btf_is_datasec(datasec_type)) {
    pr_warn("map '%s': cannot be resized, map value type is not a datasec\n",
      bpf_map__name(map));
    return -EINVAL;
  }

  /* verify datasec has at least one var */
  vlen = btf_vlen(datasec_type);
  if (vlen == 0) {
    pr_warn("map '%s': cannot be resized, map value datasec is empty\n",
      bpf_map__name(map));
    return -EINVAL;
  }

  /* verify last var in the datasec is an array */
  var = &btf_var_secinfos(datasec_type)[vlen - 1];
  var_type = btf_type_by_id(btf, var->type);
  array_type = skip_mods_and_typedefs(btf, var_type->type, NULL);
  if (!btf_is_array(array_type)) {
    pr_warn("map '%s': cannot be resized, last var must be an array\n",
      bpf_map__name(map));
    return -EINVAL;
  }

  /* verify request size aligns with array */
  array = btf_array(array_type);
  element_sz = btf__resolve_size(btf, array->type);
  if (element_sz <= 0 || (size - var->offset) % element_sz != 0) {
    pr_warn("map '%s': cannot be resized, element size (%d) doesn't align with new total size (%u)\n",
      bpf_map__name(map), element_sz, size);
    return -EINVAL;
  }

  /* create a new array based on the existing array, but with new length */
  nr_elements = (size - var->offset) / element_sz;
  new_array_id = btf__add_array(btf, array->index_type, array->type, nr_elements);
  if (new_array_id < 0)
    return new_array_id;

  /* adding a new btf type invalidates existing pointers to btf objects,
   * so refresh pointers before proceeding
   */
  datasec_type = btf_type_by_id(btf, map->btf_value_type_id);
  var = &btf_var_secinfos(datasec_type)[vlen - 1];
  var_type = btf_type_by_id(btf, var->type);

  /* finally update btf info */
  datasec_type->size = size;
  var->size = size - var->offset;
  var_type->type = new_array_id;

  return 0;
}

int bpf_map__set_value_size(struct bpf_map *map, __u32 size)
{
  if (map->fd >= 0)
    return libbpf_err(-EBUSY);

  if (map->mmaped) {
    int err;
    size_t mmap_old_sz, mmap_new_sz;

    mmap_old_sz = bpf_map_mmap_sz(map->def.value_size, map->def.max_entries);
    mmap_new_sz = bpf_map_mmap_sz(size, map->def.max_entries);
    err = bpf_map_mmap_resize(map, mmap_old_sz, mmap_new_sz);
    if (err) {
      pr_warn("map '%s': failed to resize memory-mapped region: %d\n",
        bpf_map__name(map), err);
      return err;
    }
    err = map_btf_datasec_resize(map, size);
    if (err && err != -ENOENT) {
      pr_warn("map '%s': failed to adjust resized BTF, clearing BTF key/value info: %d\n",
        bpf_map__name(map), err);
      map->btf_value_type_id = 0;
      map->btf_key_type_id = 0;
    }
  }

  map->def.value_size = size;
  return 0;
}

__u32 bpf_map__btf_key_type_id(const struct bpf_map *map)
{
  return map ? map->btf_key_type_id : 0;
}

__u32 bpf_map__btf_value_type_id(const struct bpf_map *map)
{
  return map ? map->btf_value_type_id : 0;
}

int bpf_map__set_initial_value(struct bpf_map *map,
             const void *data, size_t size)
{
  if (!map->mmaped || map->libbpf_type == LIBBPF_MAP_KCONFIG ||
      size != map->def.value_size || map->fd >= 0)
    return libbpf_err(-EINVAL);

  memcpy(map->mmaped, data, size);
  return 0;
}

void *bpf_map__initial_value(struct bpf_map *map, size_t *psize)
{
  if (!map->mmaped)
    return NULL;
  *psize = map->def.value_size;
  return map->mmaped;
}

bool bpf_map__is_internal(const struct bpf_map *map)
{
  return map->libbpf_type != LIBBPF_MAP_UNSPEC;
}

__u32 bpf_map__ifindex(const struct bpf_map *map)
{
  return map->map_ifindex;
}

int bpf_map__set_ifindex(struct bpf_map *map, __u32 ifindex)
{
  if (map->fd >= 0)
    return libbpf_err(-EBUSY);
  map->map_ifindex = ifindex;
  return 0;
}

int bpf_map__set_inner_map_fd(struct bpf_map *map, int fd)
{
  if (!bpf_map_type__is_map_in_map(map->def.type)) {
    pr_warn("error: unsupported map type\n");
    return libbpf_err(-EINVAL);
  }
  if (map->inner_map_fd != -1) {
    pr_warn("error: inner_map_fd already specified\n");
    return libbpf_err(-EINVAL);
  }
  if (map->inner_map) {
    bpf_map__destroy(map->inner_map);
    zfree(&map->inner_map);
  }
  map->inner_map_fd = fd;
  return 0;
}

static struct bpf_map *
__bpf_map__iter(const struct bpf_map *m, const struct bpf_object *obj, int i)
{
  ssize_t idx;
  struct bpf_map *s, *e;

  if (!obj || !obj->maps)
    return errno = EINVAL, NULL;

  s = obj->maps;
  e = obj->maps + obj->nr_maps;

  if ((m < s) || (m >= e)) {
    pr_warn("error in %s: map handler doesn't belong to object\n",
       __func__);
    return errno = EINVAL, NULL;
  }

  idx = (m - obj->maps) + i;
  if (idx >= obj->nr_maps || idx < 0)
    return NULL;
  return &obj->maps[idx];
}

struct bpf_map *
bpf_object__next_map(const struct bpf_object *obj, const struct bpf_map *prev)
{
  if (prev == NULL)
    return obj->maps;

  return __bpf_map__iter(prev, obj, 1);
}

struct bpf_map *
bpf_object__prev_map(const struct bpf_object *obj, const struct bpf_map *next)
{
  if (next == NULL) {
    if (!obj->nr_maps)
      return NULL;
    return obj->maps + obj->nr_maps - 1;
  }

  return __bpf_map__iter(next, obj, -1);
}

struct bpf_map *
bpf_object__find_map_by_name(const struct bpf_object *obj, const char *name)
{
  struct bpf_map *pos;

  bpf_object__for_each_map(pos, obj) {
    /* if it's a special internal map name (which always starts
     * with dot) then check if that special name matches the
     * real map name (ELF section name)
     */
    if (name[0] == '.') {
      if (pos->real_name && strcmp(pos->real_name, name) == 0)
        return pos;
      continue;
    }
    /* otherwise map name has to be an exact match */
    if (map_uses_real_name(pos)) {
      if (strcmp(pos->real_name, name) == 0)
        return pos;
      continue;
    }
    if (strcmp(pos->name, name) == 0)
      return pos;
  }
  return errno = ENOENT, NULL;
}

int
bpf_object__find_map_fd_by_name(const struct bpf_object *obj, const char *name)
{
  return bpf_map__fd(bpf_object__find_map_by_name(obj, name));
}

static int validate_map_op(const struct bpf_map *map, size_t key_sz,
         size_t value_sz, bool check_value_sz)
{
  if (map->fd <= 0)
    return -ENOENT;

  if (map->def.key_size != key_sz) {
    pr_warn("map '%s': unexpected key size %zu provided, expected %u\n",
      map->name, key_sz, map->def.key_size);
    return -EINVAL;
  }

  if (!check_value_sz)
    return 0;

  switch (map->def.type) {
  case BPF_MAP_TYPE_PERCPU_ARRAY:
  case BPF_MAP_TYPE_PERCPU_HASH:
  case BPF_MAP_TYPE_LRU_PERCPU_HASH:
  case BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE: {
    int num_cpu = libbpf_num_possible_cpus();
    size_t elem_sz = roundup(map->def.value_size, 8);

    if (value_sz != num_cpu * elem_sz) {
      pr_warn("map '%s': unexpected value size %zu provided for per-CPU map, expected %d * %zu = %zd\n",
        map->name, value_sz, num_cpu, elem_sz, num_cpu * elem_sz);
      return -EINVAL;
    }
    break;
  }
  default:
    if (map->def.value_size != value_sz) {
      pr_warn("map '%s': unexpected value size %zu provided, expected %u\n",
        map->name, value_sz, map->def.value_size);
      return -EINVAL;
    }
    break;
  }
  return 0;
}

int bpf_map__lookup_elem(const struct bpf_map *map,
       const void *key, size_t key_sz,
       void *value, size_t value_sz, __u64 flags)
{
  int err;

  err = validate_map_op(map, key_sz, value_sz, true);
  if (err)
    return libbpf_err(err);

  return bpf_map_lookup_elem_flags(map->fd, key, value, flags);
}

int bpf_map__update_elem(const struct bpf_map *map,
       const void *key, size_t key_sz,
       const void *value, size_t value_sz, __u64 flags)
{
  int err;

  err = validate_map_op(map, key_sz, value_sz, true);
  if (err)
    return libbpf_err(err);

  return bpf_map_update_elem(map->fd, key, value, flags);
}

int bpf_map__delete_elem(const struct bpf_map *map,
       const void *key, size_t key_sz, __u64 flags)
{
  int err;

  err = validate_map_op(map, key_sz, 0, false /* check_value_sz */);
  if (err)
    return libbpf_err(err);

  return bpf_map_delete_elem_flags(map->fd, key, flags);
}

int bpf_map__lookup_and_delete_elem(const struct bpf_map *map,
            const void *key, size_t key_sz,
            void *value, size_t value_sz, __u64 flags)
{
  int err;

  err = validate_map_op(map, key_sz, value_sz, true);
  if (err)
    return libbpf_err(err);

  return bpf_map_lookup_and_delete_elem_flags(map->fd, key, value, flags);
}

int bpf_map__get_next_key(const struct bpf_map *map,
        const void *cur_key, void *next_key, size_t key_sz)
{
  int err;

  err = validate_map_op(map, key_sz, 0, false /* check_value_sz */);
  if (err)
    return libbpf_err(err);

  return bpf_map_get_next_key(map->fd, cur_key, next_key);
}

long libbpf_get_error(const void *ptr)
{
  if (!IS_ERR_OR_NULL(ptr))
    return 0;

  if (IS_ERR(ptr))
    errno = -PTR_ERR(ptr);

  /* If ptr == NULL, then errno should be already set by the failing
   * API, because libbpf never returns NULL on success and it now always
   * sets errno on error. So no extra errno handling for ptr == NULL
   * case.
   */
  return -errno;
}

/* Replace link's underlying BPF program with the new one */
int bpf_link__update_program(struct bpf_link *link, struct bpf_program *prog)
{
  int ret;

  ret = bpf_link_update(bpf_link__fd(link), bpf_program__fd(prog), NULL);
  return libbpf_err_errno(ret);
}

/* Release "ownership" of underlying BPF resource (typically, BPF program
 * attached to some BPF hook, e.g., tracepoint, kprobe, etc). Disconnected
 * link, when destructed through bpf_link__destroy() call won't attempt to
 * detach/unregisted that BPF resource. This is useful in situations where,
 * say, attached BPF program has to outlive userspace program that attached it
 * in the system. Depending on type of BPF program, though, there might be
 * additional steps (like pinning BPF program in BPF FS) necessary to ensure
 * exit of userspace program doesn't trigger automatic detachment and clean up
 * inside the kernel.
 */
void bpf_link__disconnect(struct bpf_link *link)
{
  link->disconnected = true;
}

int bpf_link__destroy(struct bpf_link *link)
{
  int err = 0;

  if (IS_ERR_OR_NULL(link))
    return 0;

  if (!link->disconnected && link->detach)
    err = link->detach(link);
  if (link->pin_path)
    free(link->pin_path);
  if (link->dealloc)
    link->dealloc(link);
  else
    free(link);

  return libbpf_err(err);
}

int bpf_link__fd(const struct bpf_link *link)
{
  return link->fd;
}

const char *bpf_link__pin_path(const struct bpf_link *link)
{
  return link->pin_path;
}

static int bpf_link__detach_fd(struct bpf_link *link)
{
  return libbpf_err_errno(close(link->fd));
}

struct bpf_link *bpf_link__open(const char *path)
{
  struct bpf_link *link;
  int fd;

  fd = bpf_obj_get(path);
  if (fd < 0) {
    fd = -errno;
    pr_warn("failed to open link at %s: %d\n", path, fd);
    return libbpf_err_ptr(fd);
  }

  link = calloc(1, sizeof(*link));
  if (!link) {
    close(fd);
    return libbpf_err_ptr(-ENOMEM);
  }
  link->detach = &bpf_link__detach_fd;
  link->fd = fd;

  link->pin_path = strdup(path);
  if (!link->pin_path) {
    bpf_link__destroy(link);
    return libbpf_err_ptr(-ENOMEM);
  }

  return link;
}

int bpf_link__detach(struct bpf_link *link)
{
  return bpf_link_detach(link->fd) ? -errno : 0;
}

int bpf_link__pin(struct bpf_link *link, const char *path)
{
  int err;

  if (link->pin_path)
    return libbpf_err(-EBUSY);
  err = make_parent_dir(path);
  if (err)
    return libbpf_err(err);
  err = check_path(path);
  if (err)
    return libbpf_err(err);

  link->pin_path = strdup(path);
  if (!link->pin_path)
    return libbpf_err(-ENOMEM);

  if (bpf_obj_pin(link->fd, link->pin_path)) {
    err = -errno;
    zfree(&link->pin_path);
    return libbpf_err(err);
  }

  pr_debug("link fd=%d: pinned at %s\n", link->fd, link->pin_path);
  return 0;
}

int bpf_link__unpin(struct bpf_link *link)
{
  int err;

  if (!link->pin_path)
    return libbpf_err(-EINVAL);

  err = unlink(link->pin_path);
  if (err != 0)
    return -errno;

  pr_debug("link fd=%d: unpinned from %s\n", link->fd, link->pin_path);
  zfree(&link->pin_path);
  return 0;
}

struct bpf_link_perf {
  struct bpf_link link;
  int perf_event_fd;
  /* legacy kprobe support: keep track of probe identifier and type */
  char *legacy_probe_name;
  bool legacy_is_kprobe;
  bool legacy_is_retprobe;
};

static int remove_kprobe_event_legacy(const char *probe_name, bool retprobe);
static int remove_uprobe_event_legacy(const char *probe_name, bool retprobe);

static int bpf_link_perf_detach(struct bpf_link *link)
{
  struct bpf_link_perf *perf_link = container_of(link, struct bpf_link_perf, link);
  int err = 0;

  if (ioctl(perf_link->perf_event_fd, PERF_EVENT_IOC_DISABLE, 0) < 0)
    err = -errno;

  if (perf_link->perf_event_fd != link->fd)
    close(perf_link->perf_event_fd);
  close(link->fd);

  /* legacy uprobe/kprobe needs to be removed after perf event fd closure */
  if (perf_link->legacy_probe_name) {
    if (perf_link->legacy_is_kprobe) {
      err = remove_kprobe_event_legacy(perf_link->legacy_probe_name,
               perf_link->legacy_is_retprobe);
    } else {
      err = remove_uprobe_event_legacy(perf_link->legacy_probe_name,
               perf_link->legacy_is_retprobe);
    }
  }

  return err;
}

static void bpf_link_perf_dealloc(struct bpf_link *link)
{
  struct bpf_link_perf *perf_link = container_of(link, struct bpf_link_perf, link);

  free(perf_link->legacy_probe_name);
  free(perf_link);
}

struct bpf_link *bpf_program__attach_perf_event_opts(const struct bpf_program *prog, int pfd,
                 const struct bpf_perf_event_opts *opts)
{
  char errmsg[STRERR_BUFSIZE];
  struct bpf_link_perf *link;
  int prog_fd, link_fd = -1, err;
  bool force_ioctl_attach;

  if (!OPTS_VALID(opts, bpf_perf_event_opts))
    return libbpf_err_ptr(-EINVAL);

  if (pfd < 0) {
    pr_warn("prog '%s': invalid perf event FD %d\n",
      prog->name, pfd);
    return libbpf_err_ptr(-EINVAL);
  }
  prog_fd = bpf_program__fd(prog);
  if (prog_fd < 0) {
    pr_warn("prog '%s': can't attach BPF program w/o FD (did you load it?)\n",
      prog->name);
    return libbpf_err_ptr(-EINVAL);
  }

  link = calloc(1, sizeof(*link));
  if (!link)
    return libbpf_err_ptr(-ENOMEM);
  link->link.detach = &bpf_link_perf_detach;
  link->link.dealloc = &bpf_link_perf_dealloc;
  link->perf_event_fd = pfd;

  force_ioctl_attach = OPTS_GET(opts, force_ioctl_attach, false);
  if (kernel_supports(prog->obj, FEAT_PERF_LINK) && !force_ioctl_attach) {
    DECLARE_LIBBPF_OPTS(bpf_link_create_opts, link_opts,
      .perf_event.bpf_cookie = OPTS_GET(opts, bpf_cookie, 0));

    link_fd = bpf_link_create(prog_fd, pfd, BPF_PERF_EVENT, &link_opts);
    if (link_fd < 0) {
      err = -errno;
      pr_warn("prog '%s': failed to create BPF link for perf_event FD %d: %d (%s)\n",
        prog->name, pfd,
        err, libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
      goto err_out;
    }
    link->link.fd = link_fd;
  } else {
    if (OPTS_GET(opts, bpf_cookie, 0)) {
      pr_warn("prog '%s': user context value is not supported\n", prog->name);
      err = -EOPNOTSUPP;
      goto err_out;
    }

    if (ioctl(pfd, PERF_EVENT_IOC_SET_BPF, prog_fd) < 0) {
      err = -errno;
      pr_warn("prog '%s': failed to attach to perf_event FD %d: %s\n",
        prog->name, pfd, libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
      if (err == -EPROTO)
        pr_warn("prog '%s': try add PERF_SAMPLE_CALLCHAIN to or remove exclude_callchain_[kernel|user] from pfd %d\n",
          prog->name, pfd);
      goto err_out;
    }
    link->link.fd = pfd;
  }
  if (ioctl(pfd, PERF_EVENT_IOC_ENABLE, 0) < 0) {
    err = -errno;
    pr_warn("prog '%s': failed to enable perf_event FD %d: %s\n",
      prog->name, pfd, libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
    goto err_out;
  }

  return &link->link;
err_out:
  if (link_fd >= 0)
    close(link_fd);
  free(link);
  return libbpf_err_ptr(err);
}

struct bpf_link *bpf_program__attach_perf_event(const struct bpf_program *prog, int pfd)
{
  return bpf_program__attach_perf_event_opts(prog, pfd, NULL);
}

/*
 * this function is expected to parse integer in the range of [0, 2^31-1] from
 * given file using scanf format string fmt. If actual parsed value is
 * negative, the result might be indistinguishable from error
 */
static int parse_uint_from_file(const char *file, const char *fmt)
{
  char buf[STRERR_BUFSIZE];
  int err, ret;
  FILE *f;

  f = fopen(file, "re");
  if (!f) {
    err = -errno;
    pr_debug("failed to open '%s': %s\n", file,
       libbpf_strerror_r(err, buf, sizeof(buf)));
    return err;
  }
  err = fscanf(f, fmt, &ret);
  if (err != 1) {
    err = err == EOF ? -EIO : -errno;
    pr_debug("failed to parse '%s': %s\n", file,
      libbpf_strerror_r(err, buf, sizeof(buf)));
    fclose(f);
    return err;
  }
  fclose(f);
  return ret;
}

static int determine_kprobe_perf_type(void)
{
  const char *file = "/sys/bus/event_source/devices/kprobe/type";

  return parse_uint_from_file(file, "%d\n");
}

static int determine_uprobe_perf_type(void)
{
  const char *file = "/sys/bus/event_source/devices/uprobe/type";

  return parse_uint_from_file(file, "%d\n");
}

static int determine_kprobe_retprobe_bit(void)
{
  const char *file = "/sys/bus/event_source/devices/kprobe/format/retprobe";

  return parse_uint_from_file(file, "config:%d\n");
}

static int determine_uprobe_retprobe_bit(void)
{
  const char *file = "/sys/bus/event_source/devices/uprobe/format/retprobe";

  return parse_uint_from_file(file, "config:%d\n");
}

#define PERF_UPROBE_REF_CTR_OFFSET_BITS 32
#define PERF_UPROBE_REF_CTR_OFFSET_SHIFT 32

static int perf_event_open_probe(bool uprobe, bool retprobe, const char *name,
         uint64_t offset, int pid, size_t ref_ctr_off)
{
  const size_t attr_sz = sizeof(struct perf_event_attr);
  struct perf_event_attr attr;
  char errmsg[STRERR_BUFSIZE];
  int type, pfd;

  if ((__u64)ref_ctr_off >= (1ULL << PERF_UPROBE_REF_CTR_OFFSET_BITS))
    return -EINVAL;

  memset(&attr, 0, attr_sz);

  type = uprobe ? determine_uprobe_perf_type()
          : determine_kprobe_perf_type();
  if (type < 0) {
    pr_warn("failed to determine %s perf type: %s\n",
      uprobe ? "uprobe" : "kprobe",
      libbpf_strerror_r(type, errmsg, sizeof(errmsg)));
    return type;
  }
  if (retprobe) {
    int bit = uprobe ? determine_uprobe_retprobe_bit()
         : determine_kprobe_retprobe_bit();

    if (bit < 0) {
      pr_warn("failed to determine %s retprobe bit: %s\n",
        uprobe ? "uprobe" : "kprobe",
        libbpf_strerror_r(bit, errmsg, sizeof(errmsg)));
      return bit;
    }
    attr.config |= 1 << bit;
  }
  attr.size = attr_sz;
  attr.type = type;
  attr.config |= (__u64)ref_ctr_off << PERF_UPROBE_REF_CTR_OFFSET_SHIFT;
  attr.config1 = ptr_to_u64(name); /* kprobe_func or uprobe_path */
  attr.config2 = offset;     /* kprobe_addr or probe_offset */

  /* pid filter is meaningful only for uprobes */
  pfd = syscall(__NR_perf_event_open, &attr,
          pid < 0 ? -1 : pid /* pid */,
          pid == -1 ? 0 : -1 /* cpu */,
          -1 /* group_fd */, PERF_FLAG_FD_CLOEXEC);
  return pfd >= 0 ? pfd : -errno;
}

static int append_to_file(const char *file, const char *fmt, ...)
{
  int fd, n, err = 0;
  va_list ap;
  char buf[1024];

  va_start(ap, fmt);
  n = vsnprintf(buf, sizeof(buf), fmt, ap);
  va_end(ap);

  if (n < 0 || n >= sizeof(buf))
    return -EINVAL;

  fd = open(file, O_WRONLY | O_APPEND | O_CLOEXEC, 0);
  if (fd < 0)
    return -errno;

  if (write(fd, buf, n) < 0)
    err = -errno;

  close(fd);
  return err;
}

#define DEBUGFS "/sys/kernel/debug/tracing"
#define TRACEFS "/sys/kernel/tracing"

static bool use_debugfs(void)
{
  static int has_debugfs = -1;

  if (has_debugfs < 0)
    has_debugfs = faccessat(AT_FDCWD, DEBUGFS, F_OK, AT_EACCESS) == 0;

  return has_debugfs == 1;
}

static const char *tracefs_path(void)
{
  return use_debugfs() ? DEBUGFS : TRACEFS;
}

static const char *tracefs_kprobe_events(void)
{
  return use_debugfs() ? DEBUGFS"/kprobe_events" : TRACEFS"/kprobe_events";
}

static const char *tracefs_uprobe_events(void)
{
  return use_debugfs() ? DEBUGFS"/uprobe_events" : TRACEFS"/uprobe_events";
}

static const char *tracefs_available_filter_functions(void)
{
  return use_debugfs() ? DEBUGFS"/available_filter_functions"
           : TRACEFS"/available_filter_functions";
}

static const char *tracefs_available_filter_functions_addrs(void)
{
  return use_debugfs() ? DEBUGFS"/available_filter_functions_addrs"
           : TRACEFS"/available_filter_functions_addrs";
}

static void gen_kprobe_legacy_event_name(char *buf, size_t buf_sz,
           const char *kfunc_name, size_t offset)
{
  static int index = 0;
  int i;

  snprintf(buf, buf_sz, "libbpf_%u_%s_0x%zx_%d", getpid(), kfunc_name, offset,
     __sync_fetch_and_add(&index, 1));

  /* sanitize binary_path in the probe name */
  for (i = 0; buf[i]; i++) {
    if (!isalnum(buf[i]))
      buf[i] = '_';
  }
}

static int add_kprobe_event_legacy(const char *probe_name, bool retprobe,
           const char *kfunc_name, size_t offset)
{
  return append_to_file(tracefs_kprobe_events(), "%c:%s/%s %s+0x%zx",
            retprobe ? 'r' : 'p',
            retprobe ? "kretprobes" : "kprobes",
            probe_name, kfunc_name, offset);
}

static int remove_kprobe_event_legacy(const char *probe_name, bool retprobe)
{
  return append_to_file(tracefs_kprobe_events(), "-:%s/%s",
            retprobe ? "kretprobes" : "kprobes", probe_name);
}

static int determine_kprobe_perf_type_legacy(const char *probe_name, bool retprobe)
{
  char file[256];

  snprintf(file, sizeof(file), "%s/events/%s/%s/id",
     tracefs_path(), retprobe ? "kretprobes" : "kprobes", probe_name);

  return parse_uint_from_file(file, "%d\n");
}

static int perf_event_kprobe_open_legacy(const char *probe_name, bool retprobe,
           const char *kfunc_name, size_t offset, int pid)
{
  const size_t attr_sz = sizeof(struct perf_event_attr);
  struct perf_event_attr attr;
  char errmsg[STRERR_BUFSIZE];
  int type, pfd, err;

  err = add_kprobe_event_legacy(probe_name, retprobe, kfunc_name, offset);
  if (err < 0) {
    pr_warn("failed to add legacy kprobe event for '%s+0x%zx': %s\n",
      kfunc_name, offset,
      libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
    return err;
  }
  type = determine_kprobe_perf_type_legacy(probe_name, retprobe);
  if (type < 0) {
    err = type;
    pr_warn("failed to determine legacy kprobe event id for '%s+0x%zx': %s\n",
      kfunc_name, offset,
      libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
    goto err_clean_legacy;
  }

  memset(&attr, 0, attr_sz);
  attr.size = attr_sz;
  attr.config = type;
  attr.type = PERF_TYPE_TRACEPOINT;

  pfd = syscall(__NR_perf_event_open, &attr,
          pid < 0 ? -1 : pid, /* pid */
          pid == -1 ? 0 : -1, /* cpu */
          -1 /* group_fd */,  PERF_FLAG_FD_CLOEXEC);
  if (pfd < 0) {
    err = -errno;
    pr_warn("legacy kprobe perf_event_open() failed: %s\n",
      libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
    goto err_clean_legacy;
  }
  return pfd;

err_clean_legacy:
  /* Clear the newly added legacy kprobe_event */
  remove_kprobe_event_legacy(probe_name, retprobe);
  return err;
}

static const char *arch_specific_syscall_pfx(void)
{
#if defined(__x86_64__)
  return "x64";
#elif defined(__i386__)
  return "ia32";
#elif defined(__s390x__)
  return "s390x";
#elif defined(__s390__)
  return "s390";
#elif defined(__arm__)
  return "arm";
#elif defined(__aarch64__)
  return "arm64";
#elif defined(__mips__)
  return "mips";
#elif defined(__riscv)
  return "riscv";
#elif defined(__powerpc__)
  return "powerpc";
#elif defined(__powerpc64__)
  return "powerpc64";
#else
  return NULL;
#endif
}

static int probe_kern_syscall_wrapper(void)
{
  char syscall_name[64];
  const char *ksys_pfx;

  ksys_pfx = arch_specific_syscall_pfx();
  if (!ksys_pfx)
    return 0;

  snprintf(syscall_name, sizeof(syscall_name), "__%s_sys_bpf", ksys_pfx);

  if (determine_kprobe_perf_type() >= 0) {
    int pfd;

    pfd = perf_event_open_probe(false, false, syscall_name, 0, getpid(), 0);
    if (pfd >= 0)
      close(pfd);

    return pfd >= 0 ? 1 : 0;
  } else { /* legacy mode */
    char probe_name[128];

    gen_kprobe_legacy_event_name(probe_name, sizeof(probe_name), syscall_name, 0);
    if (add_kprobe_event_legacy(probe_name, false, syscall_name, 0) < 0)
      return 0;

    (void)remove_kprobe_event_legacy(probe_name, false);
    return 1;
  }
}

struct bpf_link *
bpf_program__attach_kprobe_opts(const struct bpf_program *prog,
        const char *func_name,
        const struct bpf_kprobe_opts *opts)
{
  DECLARE_LIBBPF_OPTS(bpf_perf_event_opts, pe_opts);
  enum probe_attach_mode attach_mode;
  char errmsg[STRERR_BUFSIZE];
  char *legacy_probe = NULL;
  struct bpf_link *link;
  size_t offset;
  bool retprobe, legacy;
  int pfd, err;

  if (!OPTS_VALID(opts, bpf_kprobe_opts))
    return libbpf_err_ptr(-EINVAL);

  attach_mode = OPTS_GET(opts, attach_mode, PROBE_ATTACH_MODE_DEFAULT);
  retprobe = OPTS_GET(opts, retprobe, false);
  offset = OPTS_GET(opts, offset, 0);
  pe_opts.bpf_cookie = OPTS_GET(opts, bpf_cookie, 0);

  legacy = determine_kprobe_perf_type() < 0;
  switch (attach_mode) {
  case PROBE_ATTACH_MODE_LEGACY:
    legacy = true;
    pe_opts.force_ioctl_attach = true;
    break;
  case PROBE_ATTACH_MODE_PERF:
    if (legacy)
      return libbpf_err_ptr(-ENOTSUP);
    pe_opts.force_ioctl_attach = true;
    break;
  case PROBE_ATTACH_MODE_LINK:
    if (legacy || !kernel_supports(prog->obj, FEAT_PERF_LINK))
      return libbpf_err_ptr(-ENOTSUP);
    break;
  case PROBE_ATTACH_MODE_DEFAULT:
    break;
  default:
    return libbpf_err_ptr(-EINVAL);
  }

  if (!legacy) {
    pfd = perf_event_open_probe(false /* uprobe */, retprobe,
              func_name, offset,
              -1 /* pid */, 0 /* ref_ctr_off */);
  } else {
    char probe_name[256];

    gen_kprobe_legacy_event_name(probe_name, sizeof(probe_name),
               func_name, offset);

    legacy_probe = strdup(probe_name);
    if (!legacy_probe)
      return libbpf_err_ptr(-ENOMEM);

    pfd = perf_event_kprobe_open_legacy(legacy_probe, retprobe, func_name,
                offset, -1 /* pid */);
  }
  if (pfd < 0) {
    err = -errno;
    pr_warn("prog '%s': failed to create %s '%s+0x%zx' perf event: %s\n",
      prog->name, retprobe ? "kretprobe" : "kprobe",
      func_name, offset,
      libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
    goto err_out;
  }
  link = bpf_program__attach_perf_event_opts(prog, pfd, &pe_opts);
  err = libbpf_get_error(link);
  if (err) {
    close(pfd);
    pr_warn("prog '%s': failed to attach to %s '%s+0x%zx': %s\n",
      prog->name, retprobe ? "kretprobe" : "kprobe",
      func_name, offset,
      libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
    goto err_clean_legacy;
  }
  if (legacy) {
    struct bpf_link_perf *perf_link = container_of(link, struct bpf_link_perf, link);

    perf_link->legacy_probe_name = legacy_probe;
    perf_link->legacy_is_kprobe = true;
    perf_link->legacy_is_retprobe = retprobe;
  }

  return link;

err_clean_legacy:
  if (legacy)
    remove_kprobe_event_legacy(legacy_probe, retprobe);
err_out:
  free(legacy_probe);
  return libbpf_err_ptr(err);
}

struct bpf_link *bpf_program__attach_kprobe(const struct bpf_program *prog,
              bool retprobe,
              const char *func_name)
{
  DECLARE_LIBBPF_OPTS(bpf_kprobe_opts, opts,
    .retprobe = retprobe,
  );

  return bpf_program__attach_kprobe_opts(prog, func_name, &opts);
}

struct bpf_link *bpf_program__attach_ksyscall(const struct bpf_program *prog,
                const char *syscall_name,
                const struct bpf_ksyscall_opts *opts)
{
  LIBBPF_OPTS(bpf_kprobe_opts, kprobe_opts);
  char func_name[128];

  if (!OPTS_VALID(opts, bpf_ksyscall_opts))
    return libbpf_err_ptr(-EINVAL);

  if (kernel_supports(prog->obj, FEAT_SYSCALL_WRAPPER)) {
    /* arch_specific_syscall_pfx() should never return NULL here
     * because it is guarded by kernel_supports(). However, since
     * compiler does not know that we have an explicit conditional
     * as well.
     */
    snprintf(func_name, sizeof(func_name), "__%s_sys_%s",
       arch_specific_syscall_pfx() ? : "", syscall_name);
  } else {
    snprintf(func_name, sizeof(func_name), "__se_sys_%s", syscall_name);
  }

  kprobe_opts.retprobe = OPTS_GET(opts, retprobe, false);
  kprobe_opts.bpf_cookie = OPTS_GET(opts, bpf_cookie, 0);

  return bpf_program__attach_kprobe_opts(prog, func_name, &kprobe_opts);
}

/* Adapted from perf/util/string.c */
bool glob_match(const char *str, const char *pat)
{
  while (*str && *pat && *pat != '*') {
    if (*pat == '?') {      /* Matches any single character */
      str++;
      pat++;
      continue;
    }
    if (*str != *pat)
      return false;
    str++;
    pat++;
  }
  /* Check wild card */
  if (*pat == '*') {
    while (*pat == '*')
      pat++;
    if (!*pat) /* Tail wild card matches all */
      return true;
    while (*str)
      if (glob_match(str++, pat))
        return true;
  }
  return !*str && !*pat;
}

struct kprobe_multi_resolve {
  const char *pattern;
  unsigned long *addrs;
  size_t cap;
  size_t cnt;
};

struct avail_kallsyms_data {
  char **syms;
  size_t cnt;
  struct kprobe_multi_resolve *res;
};

static int avail_func_cmp(const void *a, const void *b)
{
  return strcmp(*(const char **)a, *(const char **)b);
}

static int avail_kallsyms_cb(unsigned long long sym_addr, char sym_type,
           const char *sym_name, void *ctx)
{
  struct avail_kallsyms_data *data = ctx;
  struct kprobe_multi_resolve *res = data->res;
  int err;

  if (!bsearch(&sym_name, data->syms, data->cnt, sizeof(*data->syms), avail_func_cmp))
    return 0;

  err = libbpf_ensure_mem((void **)&res->addrs, &res->cap, sizeof(*res->addrs), res->cnt + 1);
  if (err)
    return err;

  res->addrs[res->cnt++] = (unsigned long)sym_addr;
  return 0;
}

static int libbpf_available_kallsyms_parse(struct kprobe_multi_resolve *res)
{
  const char *available_functions_file = tracefs_available_filter_functions();
  struct avail_kallsyms_data data;
  char sym_name[500];
  FILE *f;
  int err = 0, ret, i;
  char **syms = NULL;
  size_t cap = 0, cnt = 0;

  f = fopen(available_functions_file, "re");
  if (!f) {
    err = -errno;
    pr_warn("failed to open %s: %d\n", available_functions_file, err);
    return err;
  }

  while (true) {
    char *name;

    ret = fscanf(f, "%499s%*[^\n]\n", sym_name);
    if (ret == EOF && feof(f))
      break;

    if (ret != 1) {
      pr_warn("failed to parse available_filter_functions entry: %d\n", ret);
      err = -EINVAL;
      goto cleanup;
    }

    if (!glob_match(sym_name, res->pattern))
      continue;

    err = libbpf_ensure_mem((void **)&syms, &cap, sizeof(*syms), cnt + 1);
    if (err)
      goto cleanup;

    name = strdup(sym_name);
    if (!name) {
      err = -errno;
      goto cleanup;
    }

    syms[cnt++] = name;
  }

  /* no entries found, bail out */
  if (cnt == 0) {
    err = -ENOENT;
    goto cleanup;
  }

  /* sort available functions */
  qsort(syms, cnt, sizeof(*syms), avail_func_cmp);

  data.syms = syms;
  data.res = res;
  data.cnt = cnt;
  libbpf_kallsyms_parse(avail_kallsyms_cb, &data);

  if (res->cnt == 0)
    err = -ENOENT;

cleanup:
  for (i = 0; i < cnt; i++)
    free((char *)syms[i]);
  free(syms);

  fclose(f);
  return err;
}

static bool has_available_filter_functions_addrs(void)
{
  return access(tracefs_available_filter_functions_addrs(), R_OK) != -1;
}

static int libbpf_available_kprobes_parse(struct kprobe_multi_resolve *res)
{
  const char *available_path = tracefs_available_filter_functions_addrs();
  char sym_name[500];
  FILE *f;
  int ret, err = 0;
  unsigned long long sym_addr;

  f = fopen(available_path, "re");
  if (!f) {
    err = -errno;
    pr_warn("failed to open %s: %d\n", available_path, err);
    return err;
  }

  while (true) {
    ret = fscanf(f, "%llx %499s%*[^\n]\n", &sym_addr, sym_name);
    if (ret == EOF && feof(f))
      break;

    if (ret != 2) {
      pr_warn("failed to parse available_filter_functions_addrs entry: %d\n",
        ret);
      err = -EINVAL;
      goto cleanup;
    }

    if (!glob_match(sym_name, res->pattern))
      continue;

    err = libbpf_ensure_mem((void **)&res->addrs, &res->cap,
          sizeof(*res->addrs), res->cnt + 1);
    if (err)
      goto cleanup;

    res->addrs[res->cnt++] = (unsigned long)sym_addr;
  }

  if (res->cnt == 0)
    err = -ENOENT;

cleanup:
  fclose(f);
  return err;
}

struct bpf_link *
bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog,
              const char *pattern,
              const struct bpf_kprobe_multi_opts *opts)
{
  LIBBPF_OPTS(bpf_link_create_opts, lopts);
  struct kprobe_multi_resolve res = {
    .pattern = pattern,
  };
  struct bpf_link *link = NULL;
  char errmsg[STRERR_BUFSIZE];
  const unsigned long *addrs;
  int err, link_fd, prog_fd;
  const __u64 *cookies;
  const char **syms;
  bool retprobe;
  size_t cnt;

  if (!OPTS_VALID(opts, bpf_kprobe_multi_opts))
    return libbpf_err_ptr(-EINVAL);

  syms    = OPTS_GET(opts, syms, false);
  addrs   = OPTS_GET(opts, addrs, false);
  cnt     = OPTS_GET(opts, cnt, false);
  cookies = OPTS_GET(opts, cookies, false);

  if (!pattern && !addrs && !syms)
    return libbpf_err_ptr(-EINVAL);
  if (pattern && (addrs || syms || cookies || cnt))
    return libbpf_err_ptr(-EINVAL);
  if (!pattern && !cnt)
    return libbpf_err_ptr(-EINVAL);
  if (addrs && syms)
    return libbpf_err_ptr(-EINVAL);

  if (pattern) {
    if (has_available_filter_functions_addrs())
      err = libbpf_available_kprobes_parse(&res);
    else
      err = libbpf_available_kallsyms_parse(&res);
    if (err)
      goto error;
    addrs = res.addrs;
    cnt = res.cnt;
  }

  retprobe = OPTS_GET(opts, retprobe, false);

  lopts.kprobe_multi.syms = syms;
  lopts.kprobe_multi.addrs = addrs;
  lopts.kprobe_multi.cookies = cookies;
  lopts.kprobe_multi.cnt = cnt;
  lopts.kprobe_multi.flags = retprobe ? BPF_F_KPROBE_MULTI_RETURN : 0;

  link = calloc(1, sizeof(*link));
  if (!link) {
    err = -ENOMEM;
    goto error;
  }
  link->detach = &bpf_link__detach_fd;

  prog_fd = bpf_program__fd(prog);
  link_fd = bpf_link_create(prog_fd, 0, BPF_TRACE_KPROBE_MULTI, &lopts);
  if (link_fd < 0) {
    err = -errno;
    pr_warn("prog '%s': failed to attach: %s\n",
      prog->name, libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
    goto error;
  }
  link->fd = link_fd;
  free(res.addrs);
  return link;

error:
  free(link);
  free(res.addrs);
  return libbpf_err_ptr(err);
}

static int attach_kprobe(const struct bpf_program *prog, long cookie, struct bpf_link **link)
{
  DECLARE_LIBBPF_OPTS(bpf_kprobe_opts, opts);
  unsigned long offset = 0;
  const char *func_name;
  char *func;
  int n;

  *link = NULL;

  /* no auto-attach for SEC("kprobe") and SEC("kretprobe") */
  if (strcmp(prog->sec_name, "kprobe") == 0 || strcmp(prog->sec_name, "kretprobe") == 0)
    return 0;

  opts.retprobe = str_has_pfx(prog->sec_name, "kretprobe/");
  if (opts.retprobe)
    func_name = prog->sec_name + sizeof("kretprobe/") - 1;
  else
    func_name = prog->sec_name + sizeof("kprobe/") - 1;

  n = sscanf(func_name, "%m[a-zA-Z0-9_.]+%li", &func, &offset);
  if (n < 1) {
    pr_warn("kprobe name is invalid: %s\n", func_name);
    return -EINVAL;
  }
  if (opts.retprobe && offset != 0) {
    free(func);
    pr_warn("kretprobes do not support offset specification\n");
    return -EINVAL;
  }

  opts.offset = offset;
  *link = bpf_program__attach_kprobe_opts(prog, func, &opts);
  free(func);
  return libbpf_get_error(*link);
}

static int attach_ksyscall(const struct bpf_program *prog, long cookie, struct bpf_link **link)
{
  LIBBPF_OPTS(bpf_ksyscall_opts, opts);
  const char *syscall_name;

  *link = NULL;

  /* no auto-attach for SEC("ksyscall") and SEC("kretsyscall") */
  if (strcmp(prog->sec_name, "ksyscall") == 0 || strcmp(prog->sec_name, "kretsyscall") == 0)
    return 0;

  opts.retprobe = str_has_pfx(prog->sec_name, "kretsyscall/");
  if (opts.retprobe)
    syscall_name = prog->sec_name + sizeof("kretsyscall/") - 1;
  else
    syscall_name = prog->sec_name + sizeof("ksyscall/") - 1;

  *link = bpf_program__attach_ksyscall(prog, syscall_name, &opts);
  return *link ? 0 : -errno;
}

static int attach_kprobe_multi(const struct bpf_program *prog, long cookie, struct bpf_link **link)
{
  LIBBPF_OPTS(bpf_kprobe_multi_opts, opts);
  const char *spec;
  char *pattern;
  int n;

  *link = NULL;

  /* no auto-attach for SEC("kprobe.multi") and SEC("kretprobe.multi") */
  if (strcmp(prog->sec_name, "kprobe.multi") == 0 ||
      strcmp(prog->sec_name, "kretprobe.multi") == 0)
    return 0;

  opts.retprobe = str_has_pfx(prog->sec_name, "kretprobe.multi/");
  if (opts.retprobe)
    spec = prog->sec_name + sizeof("kretprobe.multi/") - 1;
  else
    spec = prog->sec_name + sizeof("kprobe.multi/") - 1;

  n = sscanf(spec, "%m[a-zA-Z0-9_.*?]", &pattern);
  if (n < 1) {
    pr_warn("kprobe multi pattern is invalid: %s\n", pattern);
    return -EINVAL;
  }

  *link = bpf_program__attach_kprobe_multi_opts(prog, pattern, &opts);
  free(pattern);
  return libbpf_get_error(*link);
}

static int attach_uprobe_multi(const struct bpf_program *prog, long cookie, struct bpf_link **link)
{
  char *probe_type = NULL, *binary_path = NULL, *func_name = NULL;
  LIBBPF_OPTS(bpf_uprobe_multi_opts, opts);
  int n, ret = -EINVAL;

  *link = NULL;

  n = sscanf(prog->sec_name, "%m[^/]/%m[^:]:%m[^\n]",
       &probe_type, &binary_path, &func_name);
  switch (n) {
  case 1:
    /* handle SEC("u[ret]probe") - format is valid, but auto-attach is impossible. */
    ret = 0;
    break;
  case 3:
    opts.retprobe = strcmp(probe_type, "uretprobe.multi") == 0;
    *link = bpf_program__attach_uprobe_multi(prog, -1, binary_path, func_name, &opts);
    ret = libbpf_get_error(*link);
    break;
  default:
    pr_warn("prog '%s': invalid format of section definition '%s'\n", prog->name,
      prog->sec_name);
    break;
  }
  free(probe_type);
  free(binary_path);
  free(func_name);
  return ret;
}

static void gen_uprobe_legacy_event_name(char *buf, size_t buf_sz,
           const char *binary_path, uint64_t offset)
{
  int i;

  snprintf(buf, buf_sz, "libbpf_%u_%s_0x%zx", getpid(), binary_path, (size_t)offset);

  /* sanitize binary_path in the probe name */
  for (i = 0; buf[i]; i++) {
    if (!isalnum(buf[i]))
      buf[i] = '_';
  }
}

static inline int add_uprobe_event_legacy(const char *probe_name, bool retprobe,
            const char *binary_path, size_t offset)
{
  return append_to_file(tracefs_uprobe_events(), "%c:%s/%s %s:0x%zx",
            retprobe ? 'r' : 'p',
            retprobe ? "uretprobes" : "uprobes",
            probe_name, binary_path, offset);
}

static inline int remove_uprobe_event_legacy(const char *probe_name, bool retprobe)
{
  return append_to_file(tracefs_uprobe_events(), "-:%s/%s",
            retprobe ? "uretprobes" : "uprobes", probe_name);
}

static int determine_uprobe_perf_type_legacy(const char *probe_name, bool retprobe)
{
  char file[512];

  snprintf(file, sizeof(file), "%s/events/%s/%s/id",
     tracefs_path(), retprobe ? "uretprobes" : "uprobes", probe_name);

  return parse_uint_from_file(file, "%d\n");
}

static int perf_event_uprobe_open_legacy(const char *probe_name, bool retprobe,
           const char *binary_path, size_t offset, int pid)
{
  const size_t attr_sz = sizeof(struct perf_event_attr);
  struct perf_event_attr attr;
  int type, pfd, err;

  err = add_uprobe_event_legacy(probe_name, retprobe, binary_path, offset);
  if (err < 0) {
    pr_warn("failed to add legacy uprobe event for %s:0x%zx: %d\n",
      binary_path, (size_t)offset, err);
    return err;
  }
  type = determine_uprobe_perf_type_legacy(probe_name, retprobe);
  if (type < 0) {
    err = type;
    pr_warn("failed to determine legacy uprobe event id for %s:0x%zx: %d\n",
      binary_path, offset, err);
    goto err_clean_legacy;
  }

  memset(&attr, 0, attr_sz);
  attr.size = attr_sz;
  attr.config = type;
  attr.type = PERF_TYPE_TRACEPOINT;

  pfd = syscall(__NR_perf_event_open, &attr,
          pid < 0 ? -1 : pid, /* pid */
          pid == -1 ? 0 : -1, /* cpu */
          -1 /* group_fd */,  PERF_FLAG_FD_CLOEXEC);
  if (pfd < 0) {
    err = -errno;
    pr_warn("legacy uprobe perf_event_open() failed: %d\n", err);
    goto err_clean_legacy;
  }
  return pfd;

err_clean_legacy:
  /* Clear the newly added legacy uprobe_event */
  remove_uprobe_event_legacy(probe_name, retprobe);
  return err;
}

/* Find offset of function name in archive specified by path. Currently
 * supported are .zip files that do not compress their contents, as used on
 * Android in the form of APKs, for example. "file_name" is the name of the ELF
 * file inside the archive. "func_name" matches symbol name or name@@LIB for
 * library functions.
 *
 * An overview of the APK format specifically provided here:
 * https://en.wikipedia.org/w/index.php?title=Apk_(file_format)&oldid=1139099120#Package_contents
 */
static long elf_find_func_offset_from_archive(const char *archive_path, const char *file_name,
                const char *func_name)
{
  struct zip_archive *archive;
  struct zip_entry entry;
  long ret;
  Elf *elf;

  archive = zip_archive_open(archive_path);
  if (IS_ERR(archive)) {
    ret = PTR_ERR(archive);
    pr_warn("zip: failed to open %s: %ld\n", archive_path, ret);
    return ret;
  }

  ret = zip_archive_find_entry(archive, file_name, &entry);
  if (ret) {
    pr_warn("zip: could not find archive member %s in %s: %ld\n", file_name,
      archive_path, ret);
    goto out;
  }
  pr_debug("zip: found entry for %s in %s at 0x%lx\n", file_name, archive_path,
     (unsigned long)entry.data_offset);

  if (entry.compression) {
    pr_warn("zip: entry %s of %s is compressed and cannot be handled\n", file_name,
      archive_path);
    ret = -LIBBPF_ERRNO__FORMAT;
    goto out;
  }

  elf = elf_memory((void *)entry.data, entry.data_length);
  if (!elf) {
    pr_warn("elf: could not read elf file %s from %s: %s\n", file_name, archive_path,
      elf_errmsg(-1));
    ret = -LIBBPF_ERRNO__LIBELF;
    goto out;
  }

  ret = elf_find_func_offset(elf, file_name, func_name);
  if (ret > 0) {
    pr_debug("elf: symbol address match for %s of %s in %s: 0x%x + 0x%lx = 0x%lx\n",
       func_name, file_name, archive_path, entry.data_offset, ret,
       ret + entry.data_offset);
    ret += entry.data_offset;
  }
  elf_end(elf);

out:
  zip_archive_close(archive);
  return ret;
}

static const char *arch_specific_lib_paths(void)
{
  /*
   * Based on https://packages.debian.org/sid/libc6.
   *
   * Assume that the traced program is built for the same architecture
   * as libbpf, which should cover the vast majority of cases.
   */
#if defined(__x86_64__)
  return "/lib/x86_64-linux-gnu";
#elif defined(__i386__)
  return "/lib/i386-linux-gnu";
#elif defined(__s390x__)
  return "/lib/s390x-linux-gnu";
#elif defined(__s390__)
  return "/lib/s390-linux-gnu";
#elif defined(__arm__) && defined(__SOFTFP__)
  return "/lib/arm-linux-gnueabi";
#elif defined(__arm__) && !defined(__SOFTFP__)
  return "/lib/arm-linux-gnueabihf";
#elif defined(__aarch64__)
  return "/lib/aarch64-linux-gnu";
#elif defined(__mips__) && defined(__MIPSEL__) && _MIPS_SZLONG == 64
  return "/lib/mips64el-linux-gnuabi64";
#elif defined(__mips__) && defined(__MIPSEL__) && _MIPS_SZLONG == 32
  return "/lib/mipsel-linux-gnu";
#elif defined(__powerpc64__) && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
  return "/lib/powerpc64le-linux-gnu";
#elif defined(__sparc__) && defined(__arch64__)
  return "/lib/sparc64-linux-gnu";
#elif defined(__riscv) && __riscv_xlen == 64
  return "/lib/riscv64-linux-gnu";
#else
  return NULL;
#endif
}

/* Get full path to program/shared library. */
static int resolve_full_path(const char *file, char *result, size_t result_sz)
{
  const char *search_paths[3] = {};
  int i, perm;

  if (str_has_sfx(file, ".so") || strstr(file, ".so.")) {
    search_paths[0] = getenv("LD_LIBRARY_PATH");
    search_paths[1] = "/usr/lib64:/usr/lib";
    search_paths[2] = arch_specific_lib_paths();
    perm = R_OK;
  } else {
    search_paths[0] = getenv("PATH");
    search_paths[1] = "/usr/bin:/usr/sbin";
    perm = R_OK | X_OK;
  }

  for (i = 0; i < ARRAY_SIZE(search_paths); i++) {
    const char *s;

    if (!search_paths[i])
      continue;
    for (s = search_paths[i]; s != NULL; s = strchr(s, ':')) {
      char *next_path;
      int seg_len;

      if (s[0] == ':')
        s++;
      next_path = strchr(s, ':');
      seg_len = next_path ? next_path - s : strlen(s);
      if (!seg_len)
        continue;
      snprintf(result, result_sz, "%.*s/%s", seg_len, s, file);
      /* ensure it has required permissions */
      if (faccessat(AT_FDCWD, result, perm, AT_EACCESS) < 0)
        continue;
      pr_debug("resolved '%s' to '%s'\n", file, result);
      return 0;
    }
  }
  return -ENOENT;
}

struct bpf_link *
bpf_program__attach_uprobe_multi(const struct bpf_program *prog,
         pid_t pid,
         const char *path,
         const char *func_pattern,
         const struct bpf_uprobe_multi_opts *opts)
{
  const unsigned long *ref_ctr_offsets = NULL, *offsets = NULL;
  LIBBPF_OPTS(bpf_link_create_opts, lopts);
  unsigned long *resolved_offsets = NULL;
  int err = 0, link_fd, prog_fd;
  struct bpf_link *link = NULL;
  char errmsg[STRERR_BUFSIZE];
  char full_path[PATH_MAX];
  const __u64 *cookies;
  const char **syms;
  size_t cnt;

  if (!OPTS_VALID(opts, bpf_uprobe_multi_opts))
    return libbpf_err_ptr(-EINVAL);

  syms = OPTS_GET(opts, syms, NULL);
  offsets = OPTS_GET(opts, offsets, NULL);
  ref_ctr_offsets = OPTS_GET(opts, ref_ctr_offsets, NULL);
  cookies = OPTS_GET(opts, cookies, NULL);
  cnt = OPTS_GET(opts, cnt, 0);

  /*
   * User can specify 2 mutually exclusive set of inputs:
   *
   * 1) use only path/func_pattern/pid arguments
   *
   * 2) use path/pid with allowed combinations of:
   *    syms/offsets/ref_ctr_offsets/cookies/cnt
   *
   *    - syms and offsets are mutually exclusive
   *    - ref_ctr_offsets and cookies are optional
   *
   * Any other usage results in error.
   */

  if (!path)
    return libbpf_err_ptr(-EINVAL);
  if (!func_pattern && cnt == 0)
    return libbpf_err_ptr(-EINVAL);

  if (func_pattern) {
    if (syms || offsets || ref_ctr_offsets || cookies || cnt)
      return libbpf_err_ptr(-EINVAL);
  } else {
    if (!!syms == !!offsets)
      return libbpf_err_ptr(-EINVAL);
  }

  if (func_pattern) {
    if (!strchr(path, '/')) {
      err = resolve_full_path(path, full_path, sizeof(full_path));
      if (err) {
        pr_warn("prog '%s': failed to resolve full path for '%s': %d\n",
          prog->name, path, err);
        return libbpf_err_ptr(err);
      }
      path = full_path;
    }

    err = elf_resolve_pattern_offsets(path, func_pattern,
              &resolved_offsets, &cnt);
    if (err < 0)
      return libbpf_err_ptr(err);
    offsets = resolved_offsets;
  } else if (syms) {
    err = elf_resolve_syms_offsets(path, cnt, syms, &resolved_offsets);
    if (err < 0)
      return libbpf_err_ptr(err);
    offsets = resolved_offsets;
  }

  lopts.uprobe_multi.path = path;
  lopts.uprobe_multi.offsets = offsets;
  lopts.uprobe_multi.ref_ctr_offsets = ref_ctr_offsets;
  lopts.uprobe_multi.cookies = cookies;
  lopts.uprobe_multi.cnt = cnt;
  lopts.uprobe_multi.flags = OPTS_GET(opts, retprobe, false) ? BPF_F_UPROBE_MULTI_RETURN : 0;

  if (pid == 0)
    pid = getpid();
  if (pid > 0)
    lopts.uprobe_multi.pid = pid;

  link = calloc(1, sizeof(*link));
  if (!link) {
    err = -ENOMEM;
    goto error;
  }
  link->detach = &bpf_link__detach_fd;

  prog_fd = bpf_program__fd(prog);
  link_fd = bpf_link_create(prog_fd, 0, BPF_TRACE_UPROBE_MULTI, &lopts);
  if (link_fd < 0) {
    err = -errno;
    pr_warn("prog '%s': failed to attach multi-uprobe: %s\n",
      prog->name, libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
    goto error;
  }
  link->fd = link_fd;
  free(resolved_offsets);
  return link;

error:
  free(resolved_offsets);
  free(link);
  return libbpf_err_ptr(err);
}

LIBBPF_API struct bpf_link *
bpf_program__attach_uprobe_opts(const struct bpf_program *prog, pid_t pid,
        const char *binary_path, size_t func_offset,
        const struct bpf_uprobe_opts *opts)
{
  const char *archive_path = NULL, *archive_sep = NULL;
  char errmsg[STRERR_BUFSIZE], *legacy_probe = NULL;
  DECLARE_LIBBPF_OPTS(bpf_perf_event_opts, pe_opts);
  enum probe_attach_mode attach_mode;
  char full_path[PATH_MAX];
  struct bpf_link *link;
  size_t ref_ctr_off;
  int pfd, err;
  bool retprobe, legacy;
  const char *func_name;

  if (!OPTS_VALID(opts, bpf_uprobe_opts))
    return libbpf_err_ptr(-EINVAL);

  attach_mode = OPTS_GET(opts, attach_mode, PROBE_ATTACH_MODE_DEFAULT);
  retprobe = OPTS_GET(opts, retprobe, false);
  ref_ctr_off = OPTS_GET(opts, ref_ctr_offset, 0);
  pe_opts.bpf_cookie = OPTS_GET(opts, bpf_cookie, 0);

  if (!binary_path)
    return libbpf_err_ptr(-EINVAL);

  /* Check if "binary_path" refers to an archive. */
  archive_sep = strstr(binary_path, "!/");
  if (archive_sep) {
    full_path[0] = '\0';
    libbpf_strlcpy(full_path, binary_path,
             min(sizeof(full_path), (size_t)(archive_sep - binary_path + 1)));
    archive_path = full_path;
    binary_path = archive_sep + 2;
  } else if (!strchr(binary_path, '/')) {
    err = resolve_full_path(binary_path, full_path, sizeof(full_path));
    if (err) {
      pr_warn("prog '%s': failed to resolve full path for '%s': %d\n",
        prog->name, binary_path, err);
      return libbpf_err_ptr(err);
    }
    binary_path = full_path;
  }
  func_name = OPTS_GET(opts, func_name, NULL);
  if (func_name) {
    long sym_off;

    if (archive_path) {
      sym_off = elf_find_func_offset_from_archive(archive_path, binary_path,
                    func_name);
      binary_path = archive_path;
    } else {
      sym_off = elf_find_func_offset_from_file(binary_path, func_name);
    }
    if (sym_off < 0)
      return libbpf_err_ptr(sym_off);
    func_offset += sym_off;
  }

  legacy = determine_uprobe_perf_type() < 0;
  switch (attach_mode) {
  case PROBE_ATTACH_MODE_LEGACY:
    legacy = true;
    pe_opts.force_ioctl_attach = true;
    break;
  case PROBE_ATTACH_MODE_PERF:
    if (legacy)
      return libbpf_err_ptr(-ENOTSUP);
    pe_opts.force_ioctl_attach = true;
    break;
  case PROBE_ATTACH_MODE_LINK:
    if (legacy || !kernel_supports(prog->obj, FEAT_PERF_LINK))
      return libbpf_err_ptr(-ENOTSUP);
    break;
  case PROBE_ATTACH_MODE_DEFAULT:
    break;
  default:
    return libbpf_err_ptr(-EINVAL);
  }

  if (!legacy) {
    pfd = perf_event_open_probe(true /* uprobe */, retprobe, binary_path,
              func_offset, pid, ref_ctr_off);
  } else {
    char probe_name[PATH_MAX + 64];

    if (ref_ctr_off)
      return libbpf_err_ptr(-EINVAL);

    gen_uprobe_legacy_event_name(probe_name, sizeof(probe_name),
               binary_path, func_offset);

    legacy_probe = strdup(probe_name);
    if (!legacy_probe)
      return libbpf_err_ptr(-ENOMEM);

    pfd = perf_event_uprobe_open_legacy(legacy_probe, retprobe,
                binary_path, func_offset, pid);
  }
  if (pfd < 0) {
    err = -errno;
    pr_warn("prog '%s': failed to create %s '%s:0x%zx' perf event: %s\n",
      prog->name, retprobe ? "uretprobe" : "uprobe",
      binary_path, func_offset,
      libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
    goto err_out;
  }

  link = bpf_program__attach_perf_event_opts(prog, pfd, &pe_opts);
  err = libbpf_get_error(link);
  if (err) {
    close(pfd);
    pr_warn("prog '%s': failed to attach to %s '%s:0x%zx': %s\n",
      prog->name, retprobe ? "uretprobe" : "uprobe",
      binary_path, func_offset,
      libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
    goto err_clean_legacy;
  }
  if (legacy) {
    struct bpf_link_perf *perf_link = container_of(link, struct bpf_link_perf, link);

    perf_link->legacy_probe_name = legacy_probe;
    perf_link->legacy_is_kprobe = false;
    perf_link->legacy_is_retprobe = retprobe;
  }
  return link;

err_clean_legacy:
  if (legacy)
    remove_uprobe_event_legacy(legacy_probe, retprobe);
err_out:
  free(legacy_probe);
  return libbpf_err_ptr(err);
}

/* Format of u[ret]probe section definition supporting auto-attach:
 * u[ret]probe/binary:function[+offset]
 *
 * binary can be an absolute/relative path or a filename; the latter is resolved to a
 * full binary path via bpf_program__attach_uprobe_opts.
 *
 * Specifying uprobe+ ensures we carry out strict matching; either "uprobe" must be
 * specified (and auto-attach is not possible) or the above format is specified for
 * auto-attach.
 */
static int attach_uprobe(const struct bpf_program *prog, long cookie, struct bpf_link **link)
{
  DECLARE_LIBBPF_OPTS(bpf_uprobe_opts, opts);
  char *probe_type = NULL, *binary_path = NULL, *func_name = NULL, *func_off;
  int n, c, ret = -EINVAL;
  long offset = 0;

  *link = NULL;

  n = sscanf(prog->sec_name, "%m[^/]/%m[^:]:%m[^\n]",
       &probe_type, &binary_path, &func_name);
  switch (n) {
  case 1:
    /* handle SEC("u[ret]probe") - format is valid, but auto-attach is impossible. */
    ret = 0;
    break;
  case 2:
    pr_warn("prog '%s': section '%s' missing ':function[+offset]' specification\n",
      prog->name, prog->sec_name);
    break;
  case 3:
    /* check if user specifies `+offset`, if yes, this should be
     * the last part of the string, make sure sscanf read to EOL
     */
    func_off = strrchr(func_name, '+');
    if (func_off) {
      n = sscanf(func_off, "+%li%n", &offset, &c);
      if (n == 1 && *(func_off + c) == '\0')
        func_off[0] = '\0';
      else
        offset = 0;
    }
    opts.retprobe = strcmp(probe_type, "uretprobe") == 0 ||
        strcmp(probe_type, "uretprobe.s") == 0;
    if (opts.retprobe && offset != 0) {
      pr_warn("prog '%s': uretprobes do not support offset specification\n",
        prog->name);
      break;
    }
    opts.func_name = func_name;
    *link = bpf_program__attach_uprobe_opts(prog, -1, binary_path, offset, &opts);
    ret = libbpf_get_error(*link);
    break;
  default:
    pr_warn("prog '%s': invalid format of section definition '%s'\n", prog->name,
      prog->sec_name);
    break;
  }
  free(probe_type);
  free(binary_path);
  free(func_name);

  return ret;
}

struct bpf_link *bpf_program__attach_uprobe(const struct bpf_program *prog,
              bool retprobe, pid_t pid,
              const char *binary_path,
              size_t func_offset)
{
  DECLARE_LIBBPF_OPTS(bpf_uprobe_opts, opts, .retprobe = retprobe);

  return bpf_program__attach_uprobe_opts(prog, pid, binary_path, func_offset, &opts);
}

struct bpf_link *bpf_program__attach_usdt(const struct bpf_program *prog,
            pid_t pid, const char *binary_path,
            const char *usdt_provider, const char *usdt_name,
            const struct bpf_usdt_opts *opts)
{
  char resolved_path[512];
  struct bpf_object *obj = prog->obj;
  struct bpf_link *link;
  __u64 usdt_cookie;
  int err;

  if (!OPTS_VALID(opts, bpf_uprobe_opts))
    return libbpf_err_ptr(-EINVAL);

  if (bpf_program__fd(prog) < 0) {
    pr_warn("prog '%s': can't attach BPF program w/o FD (did you load it?)\n",
      prog->name);
    return libbpf_err_ptr(-EINVAL);
  }

  if (!binary_path)
    return libbpf_err_ptr(-EINVAL);

  if (!strchr(binary_path, '/')) {
    err = resolve_full_path(binary_path, resolved_path, sizeof(resolved_path));
    if (err) {
      pr_warn("prog '%s': failed to resolve full path for '%s': %d\n",
        prog->name, binary_path, err);
      return libbpf_err_ptr(err);
    }
    binary_path = resolved_path;
  }

  /* USDT manager is instantiated lazily on first USDT attach. It will
   * be destroyed together with BPF object in bpf_object__close().
   */
  if (IS_ERR(obj->usdt_man))
    return libbpf_ptr(obj->usdt_man);
  if (!obj->usdt_man) {
    obj->usdt_man = usdt_manager_new(obj);
    if (IS_ERR(obj->usdt_man))
      return libbpf_ptr(obj->usdt_man);
  }

  usdt_cookie = OPTS_GET(opts, usdt_cookie, 0);
  link = usdt_manager_attach_usdt(obj->usdt_man, prog, pid, binary_path,
          usdt_provider, usdt_name, usdt_cookie);
  err = libbpf_get_error(link);
  if (err)
    return libbpf_err_ptr(err);
  return link;
}

static int attach_usdt(const struct bpf_program *prog, long cookie, struct bpf_link **link)
{
  char *path = NULL, *provider = NULL, *name = NULL;
  const char *sec_name;
  int n, err;

  sec_name = bpf_program__section_name(prog);
  if (strcmp(sec_name, "usdt") == 0) {
    /* no auto-attach for just SEC("usdt") */
    *link = NULL;
    return 0;
  }

  n = sscanf(sec_name, "usdt/%m[^:]:%m[^:]:%m[^:]", &path, &provider, &name);
  if (n != 3) {
    pr_warn("invalid section '%s', expected SEC(\"usdt/<path>:<provider>:<name>\")\n",
      sec_name);
    err = -EINVAL;
  } else {
    *link = bpf_program__attach_usdt(prog, -1 /* any process */, path,
             provider, name, NULL);
    err = libbpf_get_error(*link);
  }
  free(path);
  free(provider);
  free(name);
  return err;
}

static int determine_tracepoint_id(const char *tp_category,
           const char *tp_name)
{
  char file[PATH_MAX];
  int ret;

  ret = snprintf(file, sizeof(file), "%s/events/%s/%s/id",
           tracefs_path(), tp_category, tp_name);
  if (ret < 0)
    return -errno;
  if (ret >= sizeof(file)) {
    pr_debug("tracepoint %s/%s path is too long\n",
       tp_category, tp_name);
    return -E2BIG;
  }
  return parse_uint_from_file(file, "%d\n");
}

static int perf_event_open_tracepoint(const char *tp_category,
              const char *tp_name)
{
  const size_t attr_sz = sizeof(struct perf_event_attr);
  struct perf_event_attr attr;
  char errmsg[STRERR_BUFSIZE];
  int tp_id, pfd, err;

  tp_id = determine_tracepoint_id(tp_category, tp_name);
  if (tp_id < 0) {
    pr_warn("failed to determine tracepoint '%s/%s' perf event ID: %s\n",
      tp_category, tp_name,
      libbpf_strerror_r(tp_id, errmsg, sizeof(errmsg)));
    return tp_id;
  }

  memset(&attr, 0, attr_sz);
  attr.type = PERF_TYPE_TRACEPOINT;
  attr.size = attr_sz;
  attr.config = tp_id;

  pfd = syscall(__NR_perf_event_open, &attr, -1 /* pid */, 0 /* cpu */,
          -1 /* group_fd */, PERF_FLAG_FD_CLOEXEC);
  if (pfd < 0) {
    err = -errno;
    pr_warn("tracepoint '%s/%s' perf_event_open() failed: %s\n",
      tp_category, tp_name,
      libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
    return err;
  }
  return pfd;
}

struct bpf_link *bpf_program__attach_tracepoint_opts(const struct bpf_program *prog,
                 const char *tp_category,
                 const char *tp_name,
                 const struct bpf_tracepoint_opts *opts)
{
  DECLARE_LIBBPF_OPTS(bpf_perf_event_opts, pe_opts);
  char errmsg[STRERR_BUFSIZE];
  struct bpf_link *link;
  int pfd, err;

  if (!OPTS_VALID(opts, bpf_tracepoint_opts))
    return libbpf_err_ptr(-EINVAL);

  pe_opts.bpf_cookie = OPTS_GET(opts, bpf_cookie, 0);

  pfd = perf_event_open_tracepoint(tp_category, tp_name);
  if (pfd < 0) {
    pr_warn("prog '%s': failed to create tracepoint '%s/%s' perf event: %s\n",
      prog->name, tp_category, tp_name,
      libbpf_strerror_r(pfd, errmsg, sizeof(errmsg)));
    return libbpf_err_ptr(pfd);
  }
  link = bpf_program__attach_perf_event_opts(prog, pfd, &pe_opts);
  err = libbpf_get_error(link);
  if (err) {
    close(pfd);
    pr_warn("prog '%s': failed to attach to tracepoint '%s/%s': %s\n",
      prog->name, tp_category, tp_name,
      libbpf_strerror_r(err, errmsg, sizeof(errmsg)));
    return libbpf_err_ptr(err);
  }
  return link;
}

struct bpf_link *bpf_program__attach_tracepoint(const struct bpf_program *prog,
            const char *tp_category,
            const char *tp_name)
{
  return bpf_program__attach_tracepoint_opts(prog, tp_category, tp_name, NULL);
}

static int attach_tp(const struct bpf_program *prog, long cookie, struct bpf_link **link)
{
  char *sec_name, *tp_cat, *tp_name;

  *link = NULL;

  /* no auto-attach for SEC("tp") or SEC("tracepoint") */
  if (strcmp(prog->sec_name, "tp") == 0 || strcmp(prog->sec_name, "tracepoint") == 0)
    return 0;

  sec_name = strdup(prog->sec_name);
  if (!sec_name)
    return -ENOMEM;

  /* extract "tp/<category>/<name>" or "tracepoint/<category>/<name>" */
  if (str_has_pfx(prog->sec_name, "tp/"))
    tp_cat = sec_name + sizeof("tp/") - 1;
  else
    tp_cat = sec_name + sizeof("tracepoint/") - 1;
  tp_name = strchr(tp_cat, '/');
  if (!tp_name) {
    free(sec_name);
    return -EINVAL;
  }
  *tp_name = '\0';
  tp_name++;

  *link = bpf_program__attach_tracepoint(prog, tp_cat, tp_name);
  free(sec_name);
  return libbpf_get_error(*link);
}

struct bpf_link *bpf_program__attach_raw_tracepoint(const struct bpf_program *prog,
                const char *tp_name)
{
  char errmsg[STRERR_BUFSIZE];
  struct bpf_link *link;
  int prog_fd, pfd;

  prog_fd = bpf_program__fd(prog);
  if (prog_fd < 0) {
    pr_warn("prog '%s': can't attach before loaded\n", prog->name);
    return libbpf_err_ptr(-EINVAL);
  }

  link = calloc(1, sizeof(*link));
  if (!link)
    return libbpf_err_ptr(-ENOMEM);
  link->detach = &bpf_link__detach_fd;

  pfd = bpf_raw_tracepoint_open(tp_name, prog_fd);
  if (pfd < 0) {
    pfd = -errno;
    free(link);
    pr_warn("prog '%s': failed to attach to raw tracepoint '%s': %s\n",
      prog->name, tp_name, libbpf_strerror_r(pfd, errmsg, sizeof(errmsg)));
    return libbpf_err_ptr(pfd);
  }
  link->fd = pfd;
  return link;
}

static int attach_raw_tp(const struct bpf_program *prog, long cookie, struct bpf_link **link)
{
  static const char *const prefixes[] = {
    "raw_tp",
    "raw_tracepoint",
    "raw_tp.w",
    "raw_tracepoint.w",
  };
  size_t i;
  const char *tp_name = NULL;

  *link = NULL;

  for (i = 0; i < ARRAY_SIZE(prefixes); i++) {
    size_t pfx_len;

    if (!str_has_pfx(prog->sec_name, prefixes[i]))
      continue;

    pfx_len = strlen(prefixes[i]);
    /* no auto-attach case of, e.g., SEC("raw_tp") */
    if (prog->sec_name[pfx_len] == '\0')
      return 0;

    if (prog->sec_name[pfx_len] != '/')
      continue;

    tp_name = prog->sec_name + pfx_len + 1;
    break;
  }

  if (!tp_name) {
    pr_warn("prog '%s': invalid section name '%s'\n",
      prog->name, prog->sec_name);
    return -EINVAL;
  }

  *link = bpf_program__attach_raw_tracepoint(prog, tp_name);
  return libbpf_get_error(*link);
}

/* Common logic for all BPF program types that attach to a btf_id */
static struct bpf_link *bpf_program__attach_btf_id(const struct bpf_program *prog,
               const struct bpf_trace_opts *opts)
{
  LIBBPF_OPTS(bpf_link_create_opts, link_opts);
  char errmsg[STRERR_BUFSIZE];
  struct bpf_link *link;
  int prog_fd, pfd;

  if (!OPTS_VALID(opts, bpf_trace_opts))
    return libbpf_err_ptr(-EINVAL);

  prog_fd = bpf_program__fd(prog);
  if (prog_fd < 0) {
    pr_warn("prog '%s': can't attach before loaded\n", prog->name);
    return libbpf_err_ptr(-EINVAL);
  }

  link = calloc(1, sizeof(*link));
  if (!link)
    return libbpf_err_ptr(-ENOMEM);
  link->detach = &bpf_link__detach_fd;

  /* libbpf is smart enough to redirect to BPF_RAW_TRACEPOINT_OPEN on old kernels */
  link_opts.tracing.cookie = OPTS_GET(opts, cookie, 0);
  pfd = bpf_link_create(prog_fd, 0, bpf_program__expected_attach_type(prog), &link_opts);
  if (pfd < 0) {
    pfd = -errno;
    free(link);
    pr_warn("prog '%s': failed to attach: %s\n",
      prog->name, libbpf_strerror_r(pfd, errmsg, sizeof(errmsg)));
    return libbpf_err_ptr(pfd);
  }
  link->fd = pfd;
  return link;
}

struct bpf_link *bpf_program__attach_trace(const struct bpf_program *prog)
{
  return bpf_program__attach_btf_id(prog, NULL);
}

struct bpf_link *bpf_program__attach_trace_opts(const struct bpf_program *prog,
            const struct bpf_trace_opts *opts)
{
  return bpf_program__attach_btf_id(prog, opts);
}

struct bpf_link *bpf_program__attach_lsm(const struct bpf_program *prog)
{
  return bpf_program__attach_btf_id(prog, NULL);
}

static int attach_trace(const struct bpf_program *prog, long cookie, struct bpf_link **link)
{
  *link = bpf_program__attach_trace(prog);
  return libbpf_get_error(*link);
}

static int attach_lsm(const struct bpf_program *prog, long cookie, struct bpf_link **link)
{
  *link = bpf_program__attach_lsm(prog);
  return libbpf_get_error(*link);
}

static struct bpf_link *
bpf_program_attach_fd(const struct bpf_program *prog,
          int target_fd, const char *target_name,
          const struct bpf_link_create_opts *opts)
{
  enum bpf_attach_type attach_type;
  char errmsg[STRERR_BUFSIZE];
  struct bpf_link *link;
  int prog_fd, link_fd;

  prog_fd = bpf_program__fd(prog);
  if (prog_fd < 0) {
    pr_warn("prog '%s': can't attach before loaded\n", prog->name);
    return libbpf_err_ptr(-EINVAL);
  }

  link = calloc(1, sizeof(*link));
  if (!link)
    return libbpf_err_ptr(-ENOMEM);
  link->detach = &bpf_link__detach_fd;

  attach_type = bpf_program__expected_attach_type(prog);
  link_fd = bpf_link_create(prog_fd, target_fd, attach_type, opts);
  if (link_fd < 0) {
    link_fd = -errno;
    free(link);
    pr_warn("prog '%s': failed to attach to %s: %s\n",
      prog->name, target_name,
      libbpf_strerror_r(link_fd, errmsg, sizeof(errmsg)));
    return libbpf_err_ptr(link_fd);
  }
  link->fd = link_fd;
  return link;
}

struct bpf_link *
bpf_program__attach_cgroup(const struct bpf_program *prog, int cgroup_fd)
{
  return bpf_program_attach_fd(prog, cgroup_fd, "cgroup", NULL);
}

struct bpf_link *
bpf_program__attach_netns(const struct bpf_program *prog, int netns_fd)
{
  return bpf_program_attach_fd(prog, netns_fd, "netns", NULL);
}

struct bpf_link *bpf_program__attach_xdp(const struct bpf_program *prog, int ifindex)
{
  /* target_fd/target_ifindex use the same field in LINK_CREATE */
  return bpf_program_attach_fd(prog, ifindex, "xdp", NULL);
}

struct bpf_link *
bpf_program__attach_tcx(const struct bpf_program *prog, int ifindex,
      const struct bpf_tcx_opts *opts)
{
  LIBBPF_OPTS(bpf_link_create_opts, link_create_opts);
  __u32 relative_id;
  int relative_fd;

  if (!OPTS_VALID(opts, bpf_tcx_opts))
    return libbpf_err_ptr(-EINVAL);

  relative_id = OPTS_GET(opts, relative_id, 0);
  relative_fd = OPTS_GET(opts, relative_fd, 0);

  /* validate we don't have unexpected combinations of non-zero fields */
  if (!ifindex) {
    pr_warn("prog '%s': target netdevice ifindex cannot be zero\n",
      prog->name);
    return libbpf_err_ptr(-EINVAL);
  }
  if (relative_fd && relative_id) {
    pr_warn("prog '%s': relative_fd and relative_id cannot be set at the same time\n",
      prog->name);
    return libbpf_err_ptr(-EINVAL);
  }

  link_create_opts.tcx.expected_revision = OPTS_GET(opts, expected_revision, 0);
  link_create_opts.tcx.relative_fd = relative_fd;
  link_create_opts.tcx.relative_id = relative_id;
  link_create_opts.flags = OPTS_GET(opts, flags, 0);

  /* target_fd/target_ifindex use the same field in LINK_CREATE */
  return bpf_program_attach_fd(prog, ifindex, "tcx", &link_create_opts);
}

struct bpf_link *
bpf_program__attach_netkit(const struct bpf_program *prog, int ifindex,
         const struct bpf_netkit_opts *opts)
{
  LIBBPF_OPTS(bpf_link_create_opts, link_create_opts);
  __u32 relative_id;
  int relative_fd;

  if (!OPTS_VALID(opts, bpf_netkit_opts))
    return libbpf_err_ptr(-EINVAL);

  relative_id = OPTS_GET(opts, relative_id, 0);
  relative_fd = OPTS_GET(opts, relative_fd, 0);

  /* validate we don't have unexpected combinations of non-zero fields */
  if (!ifindex) {
    pr_warn("prog '%s': target netdevice ifindex cannot be zero\n",
      prog->name);
    return libbpf_err_ptr(-EINVAL);
  }
  if (relative_fd && relative_id) {
    pr_warn("prog '%s': relative_fd and relative_id cannot be set at the same time\n",
      prog->name);
    return libbpf_err_ptr(-EINVAL);
  }

  link_create_opts.netkit.expected_revision = OPTS_GET(opts, expected_revision, 0);
  link_create_opts.netkit.relative_fd = relative_fd;
  link_create_opts.netkit.relative_id = relative_id;
  link_create_opts.flags = OPTS_GET(opts, flags, 0);

  return bpf_program_attach_fd(prog, ifindex, "netkit", &link_create_opts);
}

struct bpf_link *bpf_program__attach_freplace(const struct bpf_program *prog,
                int target_fd,
                const char *attach_func_name)
{
  int btf_id;

  if (!!target_fd != !!attach_func_name) {
    pr_warn("prog '%s': supply none or both of target_fd and attach_func_name\n",
      prog->name);
    return libbpf_err_ptr(-EINVAL);
  }

  if (prog->type != BPF_PROG_TYPE_EXT) {
    pr_warn("prog '%s': only BPF_PROG_TYPE_EXT can attach as freplace",
      prog->name);
    return libbpf_err_ptr(-EINVAL);
  }

  if (target_fd) {
    LIBBPF_OPTS(bpf_link_create_opts, target_opts);

    btf_id = libbpf_find_prog_btf_id(attach_func_name, target_fd);
    if (btf_id < 0)
      return libbpf_err_ptr(btf_id);

    target_opts.target_btf_id = btf_id;

    return bpf_program_attach_fd(prog, target_fd, "freplace",
               &target_opts);
  } else {
    /* no target, so use raw_tracepoint_open for compatibility
     * with old kernels
     */
    return bpf_program__attach_trace(prog);
  }
}

struct bpf_link *
bpf_program__attach_iter(const struct bpf_program *prog,
       const struct bpf_iter_attach_opts *opts)
{
  DECLARE_LIBBPF_OPTS(bpf_link_create_opts, link_create_opts);
  char errmsg[STRERR_BUFSIZE];
  struct bpf_link *link;
  int prog_fd, link_fd;
  __u32 target_fd = 0;

  if (!OPTS_VALID(opts, bpf_iter_attach_opts))
    return libbpf_err_ptr(-EINVAL);

  link_create_opts.iter_info = OPTS_GET(opts, link_info, (void *)0);
  link_create_opts.iter_info_len = OPTS_GET(opts, link_info_len, 0);

  prog_fd = bpf_program__fd(prog);
  if (prog_fd < 0) {
    pr_warn("prog '%s': can't attach before loaded\n", prog->name);
    return libbpf_err_ptr(-EINVAL);
  }

  link = calloc(1, sizeof(*link));
  if (!link)
    return libbpf_err_ptr(-ENOMEM);
  link->detach = &bpf_link__detach_fd;

  link_fd = bpf_link_create(prog_fd, target_fd, BPF_TRACE_ITER,
          &link_create_opts);
  if (link_fd < 0) {
    link_fd = -errno;
    free(link);
    pr_warn("prog '%s': failed to attach to iterator: %s\n",
      prog->name, libbpf_strerror_r(link_fd, errmsg, sizeof(errmsg)));
    return libbpf_err_ptr(link_fd);
  }
  link->fd = link_fd;
  return link;
}

static int attach_iter(const struct bpf_program *prog, long cookie, struct bpf_link **link)
{
  *link = bpf_program__attach_iter(prog, NULL);
  return libbpf_get_error(*link);
}

struct bpf_link *bpf_program__attach_netfilter(const struct bpf_program *prog,
                 const struct bpf_netfilter_opts *opts)
{
  LIBBPF_OPTS(bpf_link_create_opts, lopts);
  struct bpf_link *link;
  int prog_fd, link_fd;

  if (!OPTS_VALID(opts, bpf_netfilter_opts))
    return libbpf_err_ptr(-EINVAL);

  prog_fd = bpf_program__fd(prog);
  if (prog_fd < 0) {
    pr_warn("prog '%s': can't attach before loaded\n", prog->name);
    return libbpf_err_ptr(-EINVAL);
  }

  link = calloc(1, sizeof(*link));
  if (!link)
    return libbpf_err_ptr(-ENOMEM);

  link->detach = &bpf_link__detach_fd;

  lopts.netfilter.pf = OPTS_GET(opts, pf, 0);
  lopts.netfilter.hooknum = OPTS_GET(opts, hooknum, 0);
  lopts.netfilter.priority = OPTS_GET(opts, priority, 0);
  lopts.netfilter.flags = OPTS_GET(opts, flags, 0);

  link_fd = bpf_link_create(prog_fd, 0, BPF_NETFILTER, &lopts);
  if (link_fd < 0) {
    char errmsg[STRERR_BUFSIZE];

    link_fd = -errno;
    free(link);
    pr_warn("prog '%s': failed to attach to netfilter: %s\n",
      prog->name, libbpf_strerror_r(link_fd, errmsg, sizeof(errmsg)));
    return libbpf_err_ptr(link_fd);
  }
  link->fd = link_fd;

  return link;
}

struct bpf_link *bpf_program__attach(const struct bpf_program *prog)
{
  struct bpf_link *link = NULL;
  int err;

  if (!prog->sec_def || !prog->sec_def->prog_attach_fn)
    return libbpf_err_ptr(-EOPNOTSUPP);

  err = prog->sec_def->prog_attach_fn(prog, prog->sec_def->cookie, &link);
  if (err)
    return libbpf_err_ptr(err);

  /* When calling bpf_program__attach() explicitly, auto-attach support
   * is expected to work, so NULL returned link is considered an error.
   * This is different for skeleton's attach, see comment in
   * bpf_object__attach_skeleton().
   */
  if (!link)
    return libbpf_err_ptr(-EOPNOTSUPP);

  return link;
}

struct bpf_link_struct_ops {
  struct bpf_link link;
  int map_fd;
};

static int bpf_link__detach_struct_ops(struct bpf_link *link)
{
  struct bpf_link_struct_ops *st_link;
  __u32 zero = 0;

  st_link = container_of(link, struct bpf_link_struct_ops, link);

  if (st_link->map_fd < 0)
    /* w/o a real link */
    return bpf_map_delete_elem(link->fd, &zero);

  return close(link->fd);
}

struct bpf_link *bpf_map__attach_struct_ops(const struct bpf_map *map)
{
  struct bpf_link_struct_ops *link;
  __u32 zero = 0;
  int err, fd;

  if (!bpf_map__is_struct_ops(map) || map->fd == -1)
    return libbpf_err_ptr(-EINVAL);

  link = calloc(1, sizeof(*link));
  if (!link)
    return libbpf_err_ptr(-EINVAL);

  /* kern_vdata should be prepared during the loading phase. */
  err = bpf_map_update_elem(map->fd, &zero, map->st_ops->kern_vdata, 0);
  /* It can be EBUSY if the map has been used to create or
   * update a link before.  We don't allow updating the value of
   * a struct_ops once it is set.  That ensures that the value
   * never changed.  So, it is safe to skip EBUSY.
   */
  if (err && (!(map->def.map_flags & BPF_F_LINK) || err != -EBUSY)) {
    free(link);
    return libbpf_err_ptr(err);
  }

  link->link.detach = bpf_link__detach_struct_ops;

  if (!(map->def.map_flags & BPF_F_LINK)) {
    /* w/o a real link */
    link->link.fd = map->fd;
    link->map_fd = -1;
    return &link->link;
  }

  fd = bpf_link_create(map->fd, 0, BPF_STRUCT_OPS, NULL);
  if (fd < 0) {
    free(link);
    return libbpf_err_ptr(fd);
  }

  link->link.fd = fd;
  link->map_fd = map->fd;

  return &link->link;
}

/*
 * Swap the back struct_ops of a link with a new struct_ops map.
 */
int bpf_link__update_map(struct bpf_link *link, const struct bpf_map *map)
{
  struct bpf_link_struct_ops *st_ops_link;
  __u32 zero = 0;
  int err;

  if (!bpf_map__is_struct_ops(map) || map->fd < 0)
    return -EINVAL;

  st_ops_link = container_of(link, struct bpf_link_struct_ops, link);
  /* Ensure the type of a link is correct */
  if (st_ops_link->map_fd < 0)
    return -EINVAL;

  err = bpf_map_update_elem(map->fd, &zero, map->st_ops->kern_vdata, 0);
  /* It can be EBUSY if the map has been used to create or
   * update a link before.  We don't allow updating the value of
   * a struct_ops once it is set.  That ensures that the value
   * never changed.  So, it is safe to skip EBUSY.
   */
  if (err && err != -EBUSY)
    return err;

  err = bpf_link_update(link->fd, map->fd, NULL);
  if (err < 0)
    return err;

  st_ops_link->map_fd = map->fd;

  return 0;
}

typedef enum bpf_perf_event_ret (*bpf_perf_event_print_t)(struct perf_event_header *hdr,
                void *private_data);

static enum bpf_perf_event_ret
perf_event_read_simple(void *mmap_mem, size_t mmap_size, size_t page_size,
           void **copy_mem, size_t *copy_size,
           bpf_perf_event_print_t fn, void *private_data)
{
  struct perf_event_mmap_page *header = mmap_mem;
  __u64 data_head = ring_buffer_read_head(header);
  __u64 data_tail = header->data_tail;
  void *base = ((__u8 *)header) + page_size;
  int ret = LIBBPF_PERF_EVENT_CONT;
  struct perf_event_header *ehdr;
  size_t ehdr_size;

  while (data_head != data_tail) {
    ehdr = base + (data_tail & (mmap_size - 1));
    ehdr_size = ehdr->size;

    if (((void *)ehdr) + ehdr_size > base + mmap_size) {
      void *copy_start = ehdr;
      size_t len_first = base + mmap_size - copy_start;
      size_t len_secnd = ehdr_size - len_first;

      if (*copy_size < ehdr_size) {
        free(*copy_mem);
        *copy_mem = malloc(ehdr_size);
        if (!*copy_mem) {
          *copy_size = 0;
          ret = LIBBPF_PERF_EVENT_ERROR;
          break;
        }
        *copy_size = ehdr_size;
      }

      memcpy(*copy_mem, copy_start, len_first);
      memcpy(*copy_mem + len_first, base, len_secnd);
      ehdr = *copy_mem;
    }

    ret = fn(ehdr, private_data);
    data_tail += ehdr_size;
    if (ret != LIBBPF_PERF_EVENT_CONT)
      break;
  }

  ring_buffer_write_tail(header, data_tail);
  return libbpf_err(ret);
}

struct perf_buffer;

struct perf_buffer_params {
  struct perf_event_attr *attr;
  /* if event_cb is specified, it takes precendence */
  perf_buffer_event_fn event_cb;
  /* sample_cb and lost_cb are higher-level common-case callbacks */
  perf_buffer_sample_fn sample_cb;
  perf_buffer_lost_fn lost_cb;
  void *ctx;
  int cpu_cnt;
  int *cpus;
  int *map_keys;
};

struct perf_cpu_buf {
  struct perf_buffer *pb;
  void *base; /* mmap()'ed memory */
  void *buf; /* for reconstructing segmented data */
  size_t buf_size;
  int fd;
  int cpu;
  int map_key;
};

struct perf_buffer {
  perf_buffer_event_fn event_cb;
  perf_buffer_sample_fn sample_cb;
  perf_buffer_lost_fn lost_cb;
  void *ctx; /* passed into callbacks */

  size_t page_size;
  size_t mmap_size;
  struct perf_cpu_buf **cpu_bufs;
  struct epoll_event *events;
  int cpu_cnt; /* number of allocated CPU buffers */
  int epoll_fd; /* perf event FD */
  int map_fd; /* BPF_MAP_TYPE_PERF_EVENT_ARRAY BPF map FD */
};

static void perf_buffer__free_cpu_buf(struct perf_buffer *pb,
              struct perf_cpu_buf *cpu_buf)
{
  if (!cpu_buf)
    return;
  if (cpu_buf->base &&
      munmap(cpu_buf->base, pb->mmap_size + pb->page_size))
    pr_warn("failed to munmap cpu_buf #%d\n", cpu_buf->cpu);
  if (cpu_buf->fd >= 0) {
    ioctl(cpu_buf->fd, PERF_EVENT_IOC_DISABLE, 0);
    close(cpu_buf->fd);
  }
  free(cpu_buf->buf);
  free(cpu_buf);
}

void perf_buffer__free(struct perf_buffer *pb)
{
  int i;

  if (IS_ERR_OR_NULL(pb))
    return;
  if (pb->cpu_bufs) {
    for (i = 0; i < pb->cpu_cnt; i++) {
      struct perf_cpu_buf *cpu_buf = pb->cpu_bufs[i];

      if (!cpu_buf)
        continue;

      bpf_map_delete_elem(pb->map_fd, &cpu_buf->map_key);
      perf_buffer__free_cpu_buf(pb, cpu_buf);
    }
    free(pb->cpu_bufs);
  }
  if (pb->epoll_fd >= 0)
    close(pb->epoll_fd);
  free(pb->events);
  free(pb);
}

static struct perf_cpu_buf *
perf_buffer__open_cpu_buf(struct perf_buffer *pb, struct perf_event_attr *attr,
        int cpu, int map_key)
{
  struct perf_cpu_buf *cpu_buf;
  char msg[STRERR_BUFSIZE];
  int err;

  cpu_buf = calloc(1, sizeof(*cpu_buf));
  if (!cpu_buf)
    return ERR_PTR(-ENOMEM);

  cpu_buf->pb = pb;
  cpu_buf->cpu = cpu;
  cpu_buf->map_key = map_key;

  cpu_buf->fd = syscall(__NR_perf_event_open, attr, -1 /* pid */, cpu,
            -1, PERF_FLAG_FD_CLOEXEC);
  if (cpu_buf->fd < 0) {
    err = -errno;
    pr_warn("failed to open perf buffer event on cpu #%d: %s\n",
      cpu, libbpf_strerror_r(err, msg, sizeof(msg)));
    goto error;
  }

  cpu_buf->base = mmap(NULL, pb->mmap_size + pb->page_size,
           PROT_READ | PROT_WRITE, MAP_SHARED,
           cpu_buf->fd, 0);
  if (cpu_buf->base == MAP_FAILED) {
    cpu_buf->base = NULL;
    err = -errno;
    pr_warn("failed to mmap perf buffer on cpu #%d: %s\n",
      cpu, libbpf_strerror_r(err, msg, sizeof(msg)));
    goto error;
  }

  if (ioctl(cpu_buf->fd, PERF_EVENT_IOC_ENABLE, 0) < 0) {
    err = -errno;
    pr_warn("failed to enable perf buffer event on cpu #%d: %s\n",
      cpu, libbpf_strerror_r(err, msg, sizeof(msg)));
    goto error;
  }

  return cpu_buf;

error:
  perf_buffer__free_cpu_buf(pb, cpu_buf);
  return (struct perf_cpu_buf *)ERR_PTR(err);
}

static struct perf_buffer *__perf_buffer__new(int map_fd, size_t page_cnt,
                struct perf_buffer_params *p);

struct perf_buffer *perf_buffer__new(int map_fd, size_t page_cnt,
             perf_buffer_sample_fn sample_cb,
             perf_buffer_lost_fn lost_cb,
             void *ctx,
             const struct perf_buffer_opts *opts)
{
  const size_t attr_sz = sizeof(struct perf_event_attr);
  struct perf_buffer_params p = {};
  struct perf_event_attr attr;
  __u32 sample_period;

  if (!OPTS_VALID(opts, perf_buffer_opts))
    return libbpf_err_ptr(-EINVAL);

  sample_period = OPTS_GET(opts, sample_period, 1);
  if (!sample_period)
    sample_period = 1;

  memset(&attr, 0, attr_sz);
  attr.size = attr_sz;
  attr.config = PERF_COUNT_SW_BPF_OUTPUT;
  attr.type = PERF_TYPE_SOFTWARE;
  attr.sample_type = PERF_SAMPLE_RAW;
  attr.sample_period = sample_period;
  attr.wakeup_events = sample_period;

  p.attr = &attr;
  p.sample_cb = sample_cb;
  p.lost_cb = lost_cb;
  p.ctx = ctx;

  return libbpf_ptr(__perf_buffer__new(map_fd, page_cnt, &p));
}

struct perf_buffer *perf_buffer__new_raw(int map_fd, size_t page_cnt,
           struct perf_event_attr *attr,
           perf_buffer_event_fn event_cb, void *ctx,
           const struct perf_buffer_raw_opts *opts)
{
  struct perf_buffer_params p = {};

  if (!attr)
    return libbpf_err_ptr(-EINVAL);

  if (!OPTS_VALID(opts, perf_buffer_raw_opts))
    return libbpf_err_ptr(-EINVAL);

  p.attr = attr;
  p.event_cb = event_cb;
  p.ctx = ctx;
  p.cpu_cnt = OPTS_GET(opts, cpu_cnt, 0);
  p.cpus = OPTS_GET(opts, cpus, NULL);
  p.map_keys = OPTS_GET(opts, map_keys, NULL);

  return libbpf_ptr(__perf_buffer__new(map_fd, page_cnt, &p));
}

static struct perf_buffer *__perf_buffer__new(int map_fd, size_t page_cnt,
                struct perf_buffer_params *p)
{
  const char *online_cpus_file = "/sys/devices/system/cpu/online";
  struct bpf_map_info map;
  char msg[STRERR_BUFSIZE];
  struct perf_buffer *pb;
  bool *online = NULL;
  __u32 map_info_len;
  int err, i, j, n;

  if (page_cnt == 0 || (page_cnt & (page_cnt - 1))) {
    pr_warn("page count should be power of two, but is %zu\n",
      page_cnt);
    return ERR_PTR(-EINVAL);
  }

  /* best-effort sanity checks */
  memset(&map, 0, sizeof(map));
  map_info_len = sizeof(map);
  err = bpf_map_get_info_by_fd(map_fd, &map, &map_info_len);
  if (err) {
    err = -errno;
    /* if BPF_OBJ_GET_INFO_BY_FD is supported, will return
     * -EBADFD, -EFAULT, or -E2BIG on real error
     */
    if (err != -EINVAL) {
      pr_warn("failed to get map info for map FD %d: %s\n",
        map_fd, libbpf_strerror_r(err, msg, sizeof(msg)));
      return ERR_PTR(err);
    }
    pr_debug("failed to get map info for FD %d; API not supported? Ignoring...\n",
       map_fd);
  } else {
    if (map.type != BPF_MAP_TYPE_PERF_EVENT_ARRAY) {
      pr_warn("map '%s' should be BPF_MAP_TYPE_PERF_EVENT_ARRAY\n",
        map.name);
      return ERR_PTR(-EINVAL);
    }
  }

  pb = calloc(1, sizeof(*pb));
  if (!pb)
    return ERR_PTR(-ENOMEM);

  pb->event_cb = p->event_cb;
  pb->sample_cb = p->sample_cb;
  pb->lost_cb = p->lost_cb;
  pb->ctx = p->ctx;

  pb->page_size = getpagesize();
  pb->mmap_size = pb->page_size * page_cnt;
  pb->map_fd = map_fd;

  pb->epoll_fd = epoll_create1(EPOLL_CLOEXEC);
  if (pb->epoll_fd < 0) {
    err = -errno;
    pr_warn("failed to create epoll instance: %s\n",
      libbpf_strerror_r(err, msg, sizeof(msg)));
    goto error;
  }

  if (p->cpu_cnt > 0) {
    pb->cpu_cnt = p->cpu_cnt;
  } else {
    pb->cpu_cnt = libbpf_num_possible_cpus();
    if (pb->cpu_cnt < 0) {
      err = pb->cpu_cnt;
      goto error;
    }
    if (map.max_entries && map.max_entries < pb->cpu_cnt)
      pb->cpu_cnt = map.max_entries;
  }

  pb->events = calloc(pb->cpu_cnt, sizeof(*pb->events));
  if (!pb->events) {
    err = -ENOMEM;
    pr_warn("failed to allocate events: out of memory\n");
    goto error;
  }
  pb->cpu_bufs = calloc(pb->cpu_cnt, sizeof(*pb->cpu_bufs));
  if (!pb->cpu_bufs) {
    err = -ENOMEM;
    pr_warn("failed to allocate buffers: out of memory\n");
    goto error;
  }

  err = parse_cpu_mask_file(online_cpus_file, &online, &n);
  if (err) {
    pr_warn("failed to get online CPU mask: %d\n", err);
    goto error;
  }

  for (i = 0, j = 0; i < pb->cpu_cnt; i++) {
    struct perf_cpu_buf *cpu_buf;
    int cpu, map_key;

    cpu = p->cpu_cnt > 0 ? p->cpus[i] : i;
    map_key = p->cpu_cnt > 0 ? p->map_keys[i] : i;

    /* in case user didn't explicitly requested particular CPUs to
     * be attached to, skip offline/not present CPUs
     */
    if (p->cpu_cnt <= 0 && (cpu >= n || !online[cpu]))
      continue;

    cpu_buf = perf_buffer__open_cpu_buf(pb, p->attr, cpu, map_key);
    if (IS_ERR(cpu_buf)) {
      err = PTR_ERR(cpu_buf);
      goto error;
    }

    pb->cpu_bufs[j] = cpu_buf;

    err = bpf_map_update_elem(pb->map_fd, &map_key,
            &cpu_buf->fd, 0);
    if (err) {
      err = -errno;
      pr_warn("failed to set cpu #%d, key %d -> perf FD %d: %s\n",
        cpu, map_key, cpu_buf->fd,
        libbpf_strerror_r(err, msg, sizeof(msg)));
      goto error;
    }

    pb->events[j].events = EPOLLIN;
    pb->events[j].data.ptr = cpu_buf;
    if (epoll_ctl(pb->epoll_fd, EPOLL_CTL_ADD, cpu_buf->fd,
            &pb->events[j]) < 0) {
      err = -errno;
      pr_warn("failed to epoll_ctl cpu #%d perf FD %d: %s\n",
        cpu, cpu_buf->fd,
        libbpf_strerror_r(err, msg, sizeof(msg)));
      goto error;
    }
    j++;
  }
  pb->cpu_cnt = j;
  free(online);

  return pb;

error:
  free(online);
  if (pb)
    perf_buffer__free(pb);
  return ERR_PTR(err);
}

struct perf_sample_raw {
  struct perf_event_header header;
  uint32_t size;
  char data[];
};

struct perf_sample_lost {
  struct perf_event_header header;
  uint64_t id;
  uint64_t lost;
  uint64_t sample_id;
};

static enum bpf_perf_event_ret
perf_buffer__process_record(struct perf_event_header *e, void *ctx)
{
  struct perf_cpu_buf *cpu_buf = ctx;
  struct perf_buffer *pb = cpu_buf->pb;
  void *data = e;

  /* user wants full control over parsing perf event */
  if (pb->event_cb)
    return pb->event_cb(pb->ctx, cpu_buf->cpu, e);

  switch (e->type) {
  case PERF_RECORD_SAMPLE: {
    struct perf_sample_raw *s = data;

    if (pb->sample_cb)
      pb->sample_cb(pb->ctx, cpu_buf->cpu, s->data, s->size);
    break;
  }
  case PERF_RECORD_LOST: {
    struct perf_sample_lost *s = data;

    if (pb->lost_cb)
      pb->lost_cb(pb->ctx, cpu_buf->cpu, s->lost);
    break;
  }
  default:
    pr_warn("unknown perf sample type %d\n", e->type);
    return LIBBPF_PERF_EVENT_ERROR;
  }
  return LIBBPF_PERF_EVENT_CONT;
}

static int perf_buffer__process_records(struct perf_buffer *pb,
          struct perf_cpu_buf *cpu_buf)
{
  enum bpf_perf_event_ret ret;

  ret = perf_event_read_simple(cpu_buf->base, pb->mmap_size,
             pb->page_size, &cpu_buf->buf,
             &cpu_buf->buf_size,
             perf_buffer__process_record, cpu_buf);
  if (ret != LIBBPF_PERF_EVENT_CONT)
    return ret;
  return 0;
}

int perf_buffer__epoll_fd(const struct perf_buffer *pb)
{
  return pb->epoll_fd;
}

int perf_buffer__poll(struct perf_buffer *pb, int timeout_ms)
{
  int i, cnt, err;

  cnt = epoll_wait(pb->epoll_fd, pb->events, pb->cpu_cnt, timeout_ms);
  if (cnt < 0)
    return -errno;

  for (i = 0; i < cnt; i++) {
    struct perf_cpu_buf *cpu_buf = pb->events[i].data.ptr;

    err = perf_buffer__process_records(pb, cpu_buf);
    if (err) {
      pr_warn("error while processing records: %d\n", err);
      return libbpf_err(err);
    }
  }
  return cnt;
}

/* Return number of PERF_EVENT_ARRAY map slots set up by this perf_buffer
 * manager.
 */
size_t perf_buffer__buffer_cnt(const struct perf_buffer *pb)
{
  return pb->cpu_cnt;
}

/*
 * Return perf_event FD of a ring buffer in *buf_idx* slot of
 * PERF_EVENT_ARRAY BPF map. This FD can be polled for new data using
 * select()/poll()/epoll() Linux syscalls.
 */
int perf_buffer__buffer_fd(const struct perf_buffer *pb, size_t buf_idx)
{
  struct perf_cpu_buf *cpu_buf;

  if (buf_idx >= pb->cpu_cnt)
    return libbpf_err(-EINVAL);

  cpu_buf = pb->cpu_bufs[buf_idx];
  if (!cpu_buf)
    return libbpf_err(-ENOENT);

  return cpu_buf->fd;
}

int perf_buffer__buffer(struct perf_buffer *pb, int buf_idx, void **buf, size_t *buf_size)
{
  struct perf_cpu_buf *cpu_buf;

  if (buf_idx >= pb->cpu_cnt)
    return libbpf_err(-EINVAL);

  cpu_buf = pb->cpu_bufs[buf_idx];
  if (!cpu_buf)
    return libbpf_err(-ENOENT);

  *buf = cpu_buf->base;
  *buf_size = pb->mmap_size;
  return 0;
}

/*
 * Consume data from perf ring buffer corresponding to slot *buf_idx* in
 * PERF_EVENT_ARRAY BPF map without waiting/polling. If there is no data to
 * consume, do nothing and return success.
 * Returns:
 *   - 0 on success;
 *   - <0 on failure.
 */
int perf_buffer__consume_buffer(struct perf_buffer *pb, size_t buf_idx)
{
  struct perf_cpu_buf *cpu_buf;

  if (buf_idx >= pb->cpu_cnt)
    return libbpf_err(-EINVAL);

  cpu_buf = pb->cpu_bufs[buf_idx];
  if (!cpu_buf)
    return libbpf_err(-ENOENT);

  return perf_buffer__process_records(pb, cpu_buf);
}

int perf_buffer__consume(struct perf_buffer *pb)
{
  int i, err;

  for (i = 0; i < pb->cpu_cnt; i++) {
    struct perf_cpu_buf *cpu_buf = pb->cpu_bufs[i];

    if (!cpu_buf)
      continue;

    err = perf_buffer__process_records(pb, cpu_buf);
    if (err) {
      pr_warn("perf_buffer: failed to process records in buffer #%d: %d\n", i, err);
      return libbpf_err(err);
    }
  }
  return 0;
}

int bpf_program__set_attach_target(struct bpf_program *prog,
           int attach_prog_fd,
           const char *attach_func_name)
{
  int btf_obj_fd = 0, btf_id = 0, err;

  if (!prog || attach_prog_fd < 0)
    return libbpf_err(-EINVAL);

  if (prog->obj->loaded)
    return libbpf_err(-EINVAL);

  if (attach_prog_fd && !attach_func_name) {
    /* remember attach_prog_fd and let bpf_program__load() find
     * BTF ID during the program load
     */
    prog->attach_prog_fd = attach_prog_fd;
    return 0;
  }

  if (attach_prog_fd) {
    btf_id = libbpf_find_prog_btf_id(attach_func_name,
             attach_prog_fd);
    if (btf_id < 0)
      return libbpf_err(btf_id);
  } else {
    if (!attach_func_name)
      return libbpf_err(-EINVAL);

    /* load btf_vmlinux, if not yet */
    err = bpf_object__load_vmlinux_btf(prog->obj, true);
    if (err)
      return libbpf_err(err);
    err = find_kernel_btf_id(prog->obj, attach_func_name,
           prog->expected_attach_type,
           &btf_obj_fd, &btf_id);
    if (err)
      return libbpf_err(err);
  }

  prog->attach_btf_id = btf_id;
  prog->attach_btf_obj_fd = btf_obj_fd;
  prog->attach_prog_fd = attach_prog_fd;
  return 0;
}

int parse_cpu_mask_str(const char *s, bool **mask, int *mask_sz)
{
  int err = 0, n, len, start, end = -1;
  bool *tmp;

  *mask = NULL;
  *mask_sz = 0;

  /* Each sub string separated by ',' has format \d+-\d+ or \d+ */
  while (*s) {
    if (*s == ',' || *s == '\n') {
      s++;
      continue;
    }
    n = sscanf(s, "%d%n-%d%n", &start, &len, &end, &len);
    if (n <= 0 || n > 2) {
      pr_warn("Failed to get CPU range %s: %d\n", s, n);
      err = -EINVAL;
      goto cleanup;
    } else if (n == 1) {
      end = start;
    }
    if (start < 0 || start > end) {
      pr_warn("Invalid CPU range [%d,%d] in %s\n",
        start, end, s);
      err = -EINVAL;
      goto cleanup;
    }
    tmp = realloc(*mask, end + 1);
    if (!tmp) {
      err = -ENOMEM;
      goto cleanup;
    }
    *mask = tmp;
    memset(tmp + *mask_sz, 0, start - *mask_sz);
    memset(tmp + start, 1, end - start + 1);
    *mask_sz = end + 1;
    s += len;
  }
  if (!*mask_sz) {
    pr_warn("Empty CPU range\n");
    return -EINVAL;
  }
  return 0;
cleanup:
  free(*mask);
  *mask = NULL;
  return err;
}

int parse_cpu_mask_file(const char *fcpu, bool **mask, int *mask_sz)
{
  int fd, err = 0, len;
  char buf[128];

  fd = open(fcpu, O_RDONLY | O_CLOEXEC);
  if (fd < 0) {
    err = -errno;
    pr_warn("Failed to open cpu mask file %s: %d\n", fcpu, err);
    return err;
  }
  len = read(fd, buf, sizeof(buf));
  close(fd);
  if (len <= 0) {
    err = len ? -errno : -EINVAL;
    pr_warn("Failed to read cpu mask from %s: %d\n", fcpu, err);
    return err;
  }
  if (len >= sizeof(buf)) {
    pr_warn("CPU mask is too big in file %s\n", fcpu);
    return -E2BIG;
  }
  buf[len] = '\0';

  return parse_cpu_mask_str(buf, mask, mask_sz);
}

int libbpf_num_possible_cpus(void)
{
  static const char *fcpu = "/sys/devices/system/cpu/possible";
  static int cpus;
  int err, n, i, tmp_cpus;
  bool *mask;

  tmp_cpus = READ_ONCE(cpus);
  if (tmp_cpus > 0)
    return tmp_cpus;

  err = parse_cpu_mask_file(fcpu, &mask, &n);
  if (err)
    return libbpf_err(err);

  tmp_cpus = 0;
  for (i = 0; i < n; i++) {
    if (mask[i])
      tmp_cpus++;
  }
  free(mask);

  WRITE_ONCE(cpus, tmp_cpus);
  return tmp_cpus;
}

static int populate_skeleton_maps(const struct bpf_object *obj,
          struct bpf_map_skeleton *maps,
          size_t map_cnt)
{
  int i;

  for (i = 0; i < map_cnt; i++) {
    struct bpf_map **map = maps[i].map;
    const char *name = maps[i].name;
    void **mmaped = maps[i].mmaped;

    *map = bpf_object__find_map_by_name(obj, name);
    if (!*map) {
      pr_warn("failed to find skeleton map '%s'\n", name);
      return -ESRCH;
    }

    /* externs shouldn't be pre-setup from user code */
    if (mmaped && (*map)->libbpf_type != LIBBPF_MAP_KCONFIG)
      *mmaped = (*map)->mmaped;
  }
  return 0;
}

static int populate_skeleton_progs(const struct bpf_object *obj,
           struct bpf_prog_skeleton *progs,
           size_t prog_cnt)
{
  int i;

  for (i = 0; i < prog_cnt; i++) {
    struct bpf_program **prog = progs[i].prog;
    const char *name = progs[i].name;

    *prog = bpf_object__find_program_by_name(obj, name);
    if (!*prog) {
      pr_warn("failed to find skeleton program '%s'\n", name);
      return -ESRCH;
    }
  }
  return 0;
}

int bpf_object__open_skeleton(struct bpf_object_skeleton *s,
            const struct bpf_object_open_opts *opts)
{
  DECLARE_LIBBPF_OPTS(bpf_object_open_opts, skel_opts,
    .object_name = s->name,
  );
  struct bpf_object *obj;
  int err;

  /* Attempt to preserve opts->object_name, unless overriden by user
   * explicitly. Overwriting object name for skeletons is discouraged,
   * as it breaks global data maps, because they contain object name
   * prefix as their own map name prefix. When skeleton is generated,
   * bpftool is making an assumption that this name will stay the same.
   */
  if (opts) {
    memcpy(&skel_opts, opts, sizeof(*opts));
    if (!opts->object_name)
      skel_opts.object_name = s->name;
  }

  obj = bpf_object__open_mem(s->data, s->data_sz, &skel_opts);
  err = libbpf_get_error(obj);
  if (err) {
    pr_warn("failed to initialize skeleton BPF object '%s': %d\n",
      s->name, err);
    return libbpf_err(err);
  }

  *s->obj = obj;
  err = populate_skeleton_maps(obj, s->maps, s->map_cnt);
  if (err) {
    pr_warn("failed to populate skeleton maps for '%s': %d\n", s->name, err);
    return libbpf_err(err);
  }

  err = populate_skeleton_progs(obj, s->progs, s->prog_cnt);
  if (err) {
    pr_warn("failed to populate skeleton progs for '%s': %d\n", s->name, err);
    return libbpf_err(err);
  }

  return 0;
}

int bpf_object__open_subskeleton(struct bpf_object_subskeleton *s)
{
  int err, len, var_idx, i;
  const char *var_name;
  const struct bpf_map *map;
  struct btf *btf;
  __u32 map_type_id;
  const struct btf_type *map_type, *var_type;
  const struct bpf_var_skeleton *var_skel;
  struct btf_var_secinfo *var;

  if (!s->obj)
    return libbpf_err(-EINVAL);

  btf = bpf_object__btf(s->obj);
  if (!btf) {
    pr_warn("subskeletons require BTF at runtime (object %s)\n",
      bpf_object__name(s->obj));
    return libbpf_err(-errno);
  }

  err = populate_skeleton_maps(s->obj, s->maps, s->map_cnt);
  if (err) {
    pr_warn("failed to populate subskeleton maps: %d\n", err);
    return libbpf_err(err);
  }

  err = populate_skeleton_progs(s->obj, s->progs, s->prog_cnt);
  if (err) {
    pr_warn("failed to populate subskeleton maps: %d\n", err);
    return libbpf_err(err);
  }

  for (var_idx = 0; var_idx < s->var_cnt; var_idx++) {
    var_skel = &s->vars[var_idx];
    map = *var_skel->map;
    map_type_id = bpf_map__btf_value_type_id(map);
    map_type = btf__type_by_id(btf, map_type_id);

    if (!btf_is_datasec(map_type)) {
      pr_warn("type for map '%1$s' is not a datasec: %2$s",
        bpf_map__name(map),
        __btf_kind_str(btf_kind(map_type)));
      return libbpf_err(-EINVAL);
    }

    len = btf_vlen(map_type);
    var = btf_var_secinfos(map_type);
    for (i = 0; i < len; i++, var++) {
      var_type = btf__type_by_id(btf, var->type);
      var_name = btf__name_by_offset(btf, var_type->name_off);
      if (strcmp(var_name, var_skel->name) == 0) {
        *var_skel->addr = map->mmaped + var->offset;
        break;
      }
    }
  }
  return 0;
}

void bpf_object__destroy_subskeleton(struct bpf_object_subskeleton *s)
{
  if (!s)
    return;
  free(s->maps);
  free(s->progs);
  free(s->vars);
  free(s);
}

int bpf_object__load_skeleton(struct bpf_object_skeleton *s)
{
  int i, err;

  err = bpf_object__load(*s->obj);
  if (err) {
    pr_warn("failed to load BPF skeleton '%s': %d\n", s->name, err);
    return libbpf_err(err);
  }

  for (i = 0; i < s->map_cnt; i++) {
    struct bpf_map *map = *s->maps[i].map;
    size_t mmap_sz = bpf_map_mmap_sz(map->def.value_size, map->def.max_entries);
    int prot, map_fd = bpf_map__fd(map);
    void **mmaped = s->maps[i].mmaped;

    if (!mmaped)
      continue;

    if (!(map->def.map_flags & BPF_F_MMAPABLE)) {
      *mmaped = NULL;
      continue;
    }

    if (map->def.map_flags & BPF_F_RDONLY_PROG)
      prot = PROT_READ;
    else
      prot = PROT_READ | PROT_WRITE;

    /* Remap anonymous mmap()-ed "map initialization image" as
     * a BPF map-backed mmap()-ed memory, but preserving the same
     * memory address. This will cause kernel to change process'
     * page table to point to a different piece of kernel memory,
     * but from userspace point of view memory address (and its
     * contents, being identical at this point) will stay the
     * same. This mapping will be released by bpf_object__close()
     * as per normal clean up procedure, so we don't need to worry
     * about it from skeleton's clean up perspective.
     */
    *mmaped = mmap(map->mmaped, mmap_sz, prot, MAP_SHARED | MAP_FIXED, map_fd, 0);
    if (*mmaped == MAP_FAILED) {
      err = -errno;
      *mmaped = NULL;
      pr_warn("failed to re-mmap() map '%s': %d\n",
         bpf_map__name(map), err);
      return libbpf_err(err);
    }
  }

  return 0;
}

int bpf_object__attach_skeleton(struct bpf_object_skeleton *s)
{
  int i, err;

  for (i = 0; i < s->prog_cnt; i++) {
    struct bpf_program *prog = *s->progs[i].prog;
    struct bpf_link **link = s->progs[i].link;

    if (!prog->autoload || !prog->autoattach)
      continue;

    /* auto-attaching not supported for this program */
    if (!prog->sec_def || !prog->sec_def->prog_attach_fn)
      continue;

    /* if user already set the link manually, don't attempt auto-attach */
    if (*link)
      continue;

    err = prog->sec_def->prog_attach_fn(prog, prog->sec_def->cookie, link);
    if (err) {
      pr_warn("prog '%s': failed to auto-attach: %d\n",
        bpf_program__name(prog), err);
      return libbpf_err(err);
    }

    /* It's possible that for some SEC() definitions auto-attach
     * is supported in some cases (e.g., if definition completely
     * specifies target information), but is not in other cases.
     * SEC("uprobe") is one such case. If user specified target
     * binary and function name, such BPF program can be
     * auto-attached. But if not, it shouldn't trigger skeleton's
     * attach to fail. It should just be skipped.
     * attach_fn signals such case with returning 0 (no error) and
     * setting link to NULL.
     */
  }

  return 0;
}

void bpf_object__detach_skeleton(struct bpf_object_skeleton *s)
{
  int i;

  for (i = 0; i < s->prog_cnt; i++) {
    struct bpf_link **link = s->progs[i].link;

    bpf_link__destroy(*link);
    *link = NULL;
  }
}

void bpf_object__destroy_skeleton(struct bpf_object_skeleton *s)
{
  if (!s)
    return;

  if (s->progs)
    bpf_object__detach_skeleton(s);
  if (s->obj)
    bpf_object__close(*s->obj);
  free(s->maps);
  free(s->progs);
  free(s);
}

Coverage Report

Created: 2023-11-27 07:06