/*

 * Copyright (C) 2009  Internet Systems Consortium, Inc. ("ISC")

 *

 * Permission to use, copy, modify, and/or distribute this software for any

 * purpose with or without fee is hereby granted, provided that the above

 * copyright notice and this permission notice appear in all copies.

 *

 * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH

 * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY

 * AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,

 * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM

 * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE

 * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR

 * PERFORMANCE OF THIS SOFTWARE.

 */

/* $Id: backtrace.c,v 1.3 2009/09/02 23:48:02 tbox Exp $ */

/*! \file */

#include "config.h"

#include <string.h>

#include <stdlib.h>

#ifdef HAVE_LIBCTRACE

#include <execinfo.h>

#endif

#include <isc/backtrace.h>

#include <isc/result.h>

#include <isc/util.h>

#ifdef ISC_PLATFORM_USEBACKTRACE

/*

 * Getting a back trace of a running process is tricky and highly platform

 * dependent.  Our current approach is as follows:

 * 1. If the system library supports the "backtrace()" function, use it.

 * 2. Otherwise, if the compiler is gcc and the architecture is x86_64 or IA64,

 *    then use gcc's (hidden) Unwind_Backtrace() function.  Note that this

 *    function doesn't work for C programs on many other architectures.

 * 3. Otherwise, if the architecture x86 or x86_64, try to unwind the stack

 *    frame following frame pointers.  This assumes the executable binary

 *    compiled with frame pointers; this is not always true for x86_64 (rather,

 *    compiler optimizations often disable frame pointers).  The validation

 *    checks in getnextframeptr() hopefully rejects bogus values stored in

 *    the RBP register in such a case.  If the backtrace function itself crashes

 *    due to this problem, the whole package should be rebuilt with

 *    --disable-backtrace.

 */

#ifdef HAVE_LIBCTRACE

#define BACKTRACE_LIBC

#elif defined(__GNUC__) && (defined(__x86_64__) || defined(__ia64__))

#define BACKTRACE_GCC

#elif defined(__x86_64__) || defined(__i386__)

#define BACKTRACE_X86STACK

#else

#define BACKTRACE_DISABLED

#endif  /* HAVE_LIBCTRACE */

#else /* !ISC_PLATFORM_USEBACKTRACE */

#define BACKTRACE_DISABLED

#endif  /* ISC_PLATFORM_USEBACKTRACE */

#ifdef BACKTRACE_LIBC

isc_result_t

isc_backtrace_gettrace(void **addrs, int maxaddrs, int *nframes) {

  int n;

  /*

   * Validate the arguments: intentionally avoid using REQUIRE().

   * See notes in backtrace.h.

   */

  if (addrs == NULL || nframes == NULL)

    return (ISC_R_FAILURE);

  /*

   * backtrace(3) includes this function itself in the address array,

   * which should be eliminated from the returned sequence.

   */

  n = backtrace(addrs, maxaddrs);

  if (n < 2)

    return (ISC_R_NOTFOUND);

  n--;

  memmove(addrs, &addrs[1], sizeof(void *) * n);

  *nframes = n;

  return (ISC_R_SUCCESS);

}

#elif defined(BACKTRACE_GCC)

extern int _Unwind_Backtrace(void* fn, void* a);

extern void* _Unwind_GetIP(void* ctx);

typedef struct {

  void **result;

  int max_depth;

  int skip_count;

  int count;

} trace_arg_t;

static int

btcallback(void *uc, void *opq) {

  trace_arg_t *arg = (trace_arg_t *)opq;

  if (arg->skip_count > 0)

    arg->skip_count--;

  else

    arg->result[arg->count++] = (void *)_Unwind_GetIP(uc);

  if (arg->count == arg->max_depth)

    return (5); /* _URC_END_OF_STACK */

  return (0); /* _URC_NO_REASON */

}

isc_result_t

isc_backtrace_gettrace(void **addrs, int maxaddrs, int *nframes) {

  trace_arg_t arg;

  /* Argument validation: see above. */

  if (addrs == NULL || nframes == NULL)

    return (ISC_R_FAILURE);

  arg.skip_count = 1;

  arg.result = addrs;

  arg.max_depth = maxaddrs;

  arg.count = 0;

  _Unwind_Backtrace(btcallback, &arg);

  *nframes = arg.count;

  return (ISC_R_SUCCESS);

}

#elif defined(BACKTRACE_X86STACK)

#ifdef __x86_64__

static unsigned long

getrbp() {

  __asm("movq %rbp, %rax\n");

}

#endif

static void **

getnextframeptr(void **sp) {

  void **newsp = (void **)*sp;

  /*

   * Perform sanity check for the new frame pointer, derived from

   * google glog.  This can actually be bogus depending on compiler.

   */

  /* prohibit the stack frames from growing downwards */

  if (newsp <= sp)

    return (NULL);

  /* A heuristics to reject "too large" frame: this actually happened. */

  if ((char *)newsp - (char *)sp > 100000)

    return (NULL);

  /*

   * Not sure if other checks used in glog are needed at this moment.

   * For our purposes we don't have to consider non-contiguous frames,

   * for example.

   */

  return (newsp);

}

isc_result_t

isc_backtrace_gettrace(void **addrs, int maxaddrs, int *nframes) {

  int i = 0;

  void **sp;

  /* Argument validation: see above. */

  if (addrs == NULL || nframes == NULL)

    return (ISC_R_FAILURE);

#ifdef __x86_64__

  sp = (void **)getrbp();

  if (sp == NULL)

    return (ISC_R_NOTFOUND);

  /*

   * sp is the frame ptr of this function itself due to the call to

   * getrbp(), so need to unwind one frame for consistency.

   */

  sp = getnextframeptr(sp);

#else

  /*

   * i386: the frame pointer is stored 2 words below the address for the

   * first argument.  Note that the body of this function cannot be

   * inlined since it depends on the address of the function argument.

   */

  sp = (void **)&addrs - 2;

#endif

  while (sp != NULL && i < maxaddrs) {

    addrs[i++] = *(sp + 1);

    sp = getnextframeptr(sp);

  }

  *nframes = i;

  return (ISC_R_SUCCESS);

}

#elif defined(BACKTRACE_DISABLED)

isc_result_t

isc_backtrace_gettrace(void **addrs, int maxaddrs, int *nframes) {

  /* Argument validation: see above. */

  if (addrs == NULL || nframes == NULL)

    return (ISC_R_FAILURE);

  UNUSED(maxaddrs);

  return (ISC_R_NOTIMPLEMENTED);

}

#endif

isc_result_t

isc_backtrace_getsymbolfromindex(int idx, const void **addrp,

         const char **symbolp)

{

  REQUIRE(addrp != NULL && *addrp == NULL);

  REQUIRE(symbolp != NULL && *symbolp == NULL);

  if (idx < 0 || idx >= isc__backtrace_nsymbols)

    return (ISC_R_RANGE);

  *addrp = isc__backtrace_symtable[idx].addr;

  *symbolp = isc__backtrace_symtable[idx].symbol;

  return (ISC_R_SUCCESS);

}

static int

symtbl_compare(const void *addr, const void *entryarg) {

  const isc_backtrace_symmap_t *entry = entryarg;

  const isc_backtrace_symmap_t *end =

    &isc__backtrace_symtable[isc__backtrace_nsymbols - 1];

  if (isc__backtrace_nsymbols == 1 || entry == end) {

    if (addr >= entry->addr) {

      /*

       * If addr is equal to or larger than that of the last

       * entry of the table, we cannot be sure if this is

       * within a valid range so we consider it valid.

       */

      return (0);

    }

    return (-1);

  }

  /* entry + 1 is a valid entry from now on. */

  if (addr < entry->addr)

    return (-1);

  else if (addr >= (entry + 1)->addr)

    return (1);

  return (0);

}

isc_result_t

isc_backtrace_getsymbol(const void *addr, const char **symbolp,

      unsigned long *offsetp)

{

  isc_result_t result = ISC_R_SUCCESS;

  isc_backtrace_symmap_t *found;

  /*

   * Validate the arguments: intentionally avoid using REQUIRE().

   * See notes in backtrace.h.

   */

  if (symbolp == NULL || *symbolp != NULL || offsetp == NULL)

    return (ISC_R_FAILURE);

  if (isc__backtrace_nsymbols < 1)

    return (ISC_R_NOTFOUND);

  /*

   * Search the table for the entry that meets:

   * entry.addr <= addr < next_entry.addr.

   */

  found = bsearch(addr, isc__backtrace_symtable, isc__backtrace_nsymbols,

      sizeof(isc__backtrace_symtable[0]), symtbl_compare);

  if (found == NULL)

    result = ISC_R_NOTFOUND;

  else {

    *symbolp = found->symbol;

    *offsetp = (u_long)((const char *)addr - (char *)found->addr);

  }

  return (result);

}