/* gen-sframe.c - Support for generating SFrame section.

   Copyright (C) 2022-2024 Free Software Foundation, Inc.

   This file is part of GAS, the GNU Assembler.

   GAS is free software; you can redistribute it and/or modify

   it under the terms of the GNU General Public License as published by

   the Free Software Foundation; either version 3, or (at your option)

   any later version.

   GAS is distributed in the hope that it will be useful,

   but WITHOUT ANY WARRANTY; without even the implied warranty of

   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License

   along with GAS; see the file COPYING.  If not, write to the Free

   Software Foundation, 51 Franklin Street - Fifth Floor, Boston, MA

   02110-1301, USA.  */

#include "as.h"

#include "subsegs.h"

#include "sframe.h"

#include "gen-sframe.h"

#include "dw2gencfi.h"

#ifdef support_sframe_p

/* By default, use 32-bit relocations from .sframe into .text.  */

#ifndef SFRAME_RELOC_SIZE

# define SFRAME_RELOC_SIZE 4

#endif

/* Whether frame row entries track RA.

   A target may not need return address tracking for stack tracing.  If it

   does need the same, SFRAME_CFA_RA_REG must be defined with the return

   address register number.  */

#if defined (sframe_ra_tracking_p) && defined (SFRAME_CFA_RA_REG)

# ifndef SFRAME_FRE_RA_TRACKING

# define SFRAME_FRE_RA_TRACKING 1

# endif

#endif

/* SFrame FRE type selection optimization is an optimization for size.

   There are three flavors of SFrame FRE representation in the binary format:

     - sframe_frame_row_entry_addr1 where the FRE start address is 1 byte.

     - sframe_frame_row_entry_addr2 where the FRE start address is 2 bytes.

     - sframe_frame_row_entry_addr4 where the FRE start address is 4 bytes.

   Note that in the SFrame format, all SFrame FREs of a function use one

   single representation.  The SFrame FRE type itself is identified via the

   information in the SFrame FDE function info.

   Now, to select the minimum required one from the list above, one needs to

   make a decision based on the size (in bytes) of the function.

   As a result, for this optimization, some fragments (generated with a new

   type rs_sframe) for the SFrame section are fixed up later.

   This optimization (for size) is enabled by default.  */

#ifndef SFRAME_FRE_TYPE_SELECTION_OPT

# define SFRAME_FRE_TYPE_SELECTION_OPT 1

#endif

/* Emit a single byte into the current segment.  */

static inline void

out_one (int byte)

{

  FRAG_APPEND_1_CHAR (byte);

}

/* Emit a two-byte word into the current segment.  */

static inline void

out_two (int data)

{

  md_number_to_chars (frag_more (2), data, 2);

}

/* Emit a four byte word into the current segment.  */

static inline void

out_four (int data)

{

  md_number_to_chars (frag_more (4), data, 4);

}

/* Get the start address symbol from the DWARF FDE.  */

static symbolS*

get_dw_fde_start_addrS (const struct fde_entry *dw_fde)

{

  return dw_fde->start_address;

}

/* Get the start address symbol from the DWARF FDE.  */

static symbolS*

get_dw_fde_end_addrS (const struct fde_entry *dw_fde)

{

  return dw_fde->end_address;

}

/* Get whether PAUTH B key is used.  */

static bool

get_dw_fde_pauth_b_key_p (const struct fde_entry *dw_fde ATTRIBUTE_UNUSED)

{

#ifdef tc_fde_entry_extras

  return (dw_fde->pauth_key == AARCH64_PAUTH_KEY_B);

#else

  return false;

#endif

}

/* SFrame Frame Row Entry (FRE) related functions.  */

static void

sframe_fre_set_begin_addr (struct sframe_row_entry *fre, symbolS *beginS)

{

  fre->pc_begin = beginS;

}

static void

sframe_fre_set_end_addr (struct sframe_row_entry *fre, symbolS *endS)

{

  fre->pc_end = endS;

}

static void

sframe_fre_set_cfa_base_reg (struct sframe_row_entry *fre,

           unsigned int cfa_base_reg)

{

  fre->cfa_base_reg = cfa_base_reg;

  fre->merge_candidate = false;

}

static void

sframe_fre_set_cfa_offset (struct sframe_row_entry *fre,

         offsetT cfa_offset)

{

  fre->cfa_offset = cfa_offset;

  fre->merge_candidate = false;

}

#ifdef SFRAME_FRE_RA_TRACKING

static void

sframe_fre_set_ra_track (struct sframe_row_entry *fre, offsetT ra_offset)

{

  fre->ra_loc = SFRAME_FRE_ELEM_LOC_STACK;

  fre->ra_offset = ra_offset;

  fre->merge_candidate = false;

}

#endif

static void

sframe_fre_set_bp_track (struct sframe_row_entry *fre, offsetT bp_offset)

{

  fre->bp_loc = SFRAME_FRE_ELEM_LOC_STACK;

  fre->bp_offset = bp_offset;

  fre->merge_candidate = false;

}

/* All stack offset values within an FRE are uniformly encoded in the same

   number of bytes.  The size of the stack offset values will, however, vary

   across FREs.  */

#define VALUE_8BIT  0x7f

#define VALUE_16BIT 0x7fff

#define VALUE_32BIT 0x7fffffff

#define VALUE_64BIT 0x7fffffffffffffff

/* Given a signed offset, return the size in bytes needed to represent it.  */

static unsigned int

get_offset_size_in_bytes (offsetT value)

{

  unsigned int size = 0;

  if (value <= VALUE_8BIT && value >= (offsetT) -VALUE_8BIT)

    size = 1;

  else if (value <= VALUE_16BIT && value >= (offsetT) -VALUE_16BIT)

    size = 2;

  else if (value <= VALUE_32BIT && value >= (offsetT) -VALUE_32BIT)

    size = 4;

  else if ((sizeof (offsetT) > 4) && (value <= (offsetT) VALUE_64BIT

              && value >= (offsetT) -VALUE_64BIT))

    size = 8;

  return size;

}

#define SFRAME_FRE_OFFSET_FUNC_MAP_INDEX_1B  0 /* SFRAME_FRE_OFFSET_1B.  */

#define SFRAME_FRE_OFFSET_FUNC_MAP_INDEX_2B  1 /* SFRAME_FRE_OFFSET_2B.  */

#define SFRAME_FRE_OFFSET_FUNC_MAP_INDEX_4B  2 /* SFRAME_FRE_OFFSET_4B.  */

#define SFRAME_FRE_OFFSET_FUNC_MAP_INDEX_8B  3 /* Not supported in SFrame.  */

#define SFRAME_FRE_OFFSET_FUNC_MAP_INDEX_MAX SFRAME_FRE_OFFSET_FUNC_MAP_INDEX_8B

/* Helper struct for mapping offset size to output functions.  */

struct sframe_fre_offset_func_map

{

  unsigned int offset_size;

  void (*out_func)(int);

};

/* Given an OFFSET_SIZE, return the size in bytes needed to represent it.  */

static unsigned int

sframe_fre_offset_func_map_index (unsigned int offset_size)

{

  unsigned int idx = SFRAME_FRE_OFFSET_FUNC_MAP_INDEX_MAX;

  switch (offset_size)

    {

      case SFRAME_FRE_OFFSET_1B:

  idx = SFRAME_FRE_OFFSET_FUNC_MAP_INDEX_1B;

  break;

      case SFRAME_FRE_OFFSET_2B:

  idx = SFRAME_FRE_OFFSET_FUNC_MAP_INDEX_2B;

  break;

      case SFRAME_FRE_OFFSET_4B:

  idx = SFRAME_FRE_OFFSET_FUNC_MAP_INDEX_4B;

  break;

      default:

  /* Not supported in SFrame.  */

  break;

    }

  return idx;

}

/* Mapping from offset size to the output function to emit the value.  */

static const

struct sframe_fre_offset_func_map

fre_offset_func_map[SFRAME_FRE_OFFSET_FUNC_MAP_INDEX_MAX+1] =

{

  { SFRAME_FRE_OFFSET_1B, out_one },

  { SFRAME_FRE_OFFSET_2B, out_two },

  { SFRAME_FRE_OFFSET_4B, out_four },

  { -1, NULL } /* Not Supported in SFrame.  */

};

/* SFrame version specific operations access.  */

static struct sframe_version_ops sframe_ver_ops;

/* SFrame (SFRAME_VERSION_1) set FRE info.  */

static unsigned char

sframe_v1_set_fre_info (unsigned int base_reg, unsigned int num_offsets,

      unsigned int offset_size, bool mangled_ra_p)

{

  unsigned char fre_info;

  fre_info = SFRAME_V1_FRE_INFO (base_reg, num_offsets, offset_size);

  fre_info = SFRAME_V1_FRE_INFO_UPDATE_MANGLED_RA_P (mangled_ra_p, fre_info);

  return fre_info;

}

/* SFrame (SFRAME_VERSION_1) set function info.  */

static unsigned char

sframe_v1_set_func_info (unsigned int fde_type, unsigned int fre_type,

       unsigned int pauth_key)

{

  unsigned char func_info;

  func_info = SFRAME_V1_FUNC_INFO (fde_type, fre_type);

  func_info = SFRAME_V1_FUNC_INFO_UPDATE_PAUTH_KEY (pauth_key, func_info);

  return func_info;

}

/* SFrame version specific operations setup.  */

static void

sframe_set_version (uint32_t sframe_version ATTRIBUTE_UNUSED)

{

  sframe_ver_ops.format_version = SFRAME_VERSION_2;

  /* These operations remain the same for SFRAME_VERSION_2 as fre_info and

     func_info have not changed from SFRAME_VERSION_1.  */

  sframe_ver_ops.set_fre_info = sframe_v1_set_fre_info;

  sframe_ver_ops.set_func_info = sframe_v1_set_func_info;

}

/* SFrame set FRE info.  */

static unsigned char

sframe_set_fre_info (unsigned int base_reg, unsigned int num_offsets,

         unsigned int offset_size, bool mangled_ra_p)

{

  return sframe_ver_ops.set_fre_info (base_reg, num_offsets,

              offset_size, mangled_ra_p);

}

/* SFrame set func info. */

static unsigned char

sframe_set_func_info (unsigned int fde_type, unsigned int fre_type,

          unsigned int pauth_key)

{

  return sframe_ver_ops.set_func_info (fde_type, fre_type, pauth_key);

}

/* Get the number of SFrame FDEs for the current file.  */

static unsigned int

get_num_sframe_fdes (void);

/* Get the number of SFrame frame row entries for the current file.  */

static unsigned int

get_num_sframe_fres (void);

/* Get CFA base register ID as represented in SFrame Frame Row Entry.  */

static unsigned int

get_fre_base_reg_id (struct sframe_row_entry *sframe_fre)

{

  unsigned int cfi_insn_cfa_base_reg = sframe_fre->cfa_base_reg;

  unsigned fre_base_reg = SFRAME_BASE_REG_SP;

  if (cfi_insn_cfa_base_reg == SFRAME_CFA_FP_REG)

    fre_base_reg = SFRAME_BASE_REG_FP;

  /* Only one bit is reserved in SFRAME_VERSION_1.  */

  gas_assert (fre_base_reg == SFRAME_BASE_REG_SP

        || fre_base_reg == SFRAME_BASE_REG_FP);

  return fre_base_reg;

}

/* Get number of offsets necessary for the SFrame Frame Row Entry.  */

static unsigned int

get_fre_num_offsets (struct sframe_row_entry *sframe_fre)

{

  /* Atleast 1 must always be present (to recover CFA).  */

  unsigned int fre_num_offsets = 1;

  if (sframe_fre->bp_loc == SFRAME_FRE_ELEM_LOC_STACK)

    fre_num_offsets++;

#ifdef SFRAME_FRE_RA_TRACKING

  if (sframe_fre->ra_loc == SFRAME_FRE_ELEM_LOC_STACK)

    fre_num_offsets++;

#endif

  return fre_num_offsets;

}

/* Get the minimum necessary offset size (in bytes) for this

   SFrame frame row entry.  */

static unsigned int

sframe_get_fre_offset_size (struct sframe_row_entry *sframe_fre)

{

  unsigned int max_offset_size = 0;

  unsigned int cfa_offset_size = 0;

  unsigned int bp_offset_size = 0;

  unsigned int ra_offset_size = 0;

  unsigned int fre_offset_size = 0;

  /* What size of offsets appear in this frame row entry.  */

  cfa_offset_size = get_offset_size_in_bytes (sframe_fre->cfa_offset);

  if (sframe_fre->bp_loc == SFRAME_FRE_ELEM_LOC_STACK)

    bp_offset_size = get_offset_size_in_bytes (sframe_fre->bp_offset);

#ifdef SFRAME_FRE_RA_TRACKING

  if (sframe_ra_tracking_p ()

      && sframe_fre->ra_loc == SFRAME_FRE_ELEM_LOC_STACK)

    ra_offset_size = get_offset_size_in_bytes (sframe_fre->ra_offset);

#endif

  /* Get the maximum size needed to represent the offsets.  */

  max_offset_size = cfa_offset_size;

  if (bp_offset_size > max_offset_size)

    max_offset_size = bp_offset_size;

  if (ra_offset_size > max_offset_size)

    max_offset_size = ra_offset_size;

  gas_assert (max_offset_size);

  switch (max_offset_size)

    {

    case 1:

      fre_offset_size = SFRAME_FRE_OFFSET_1B;

      break;

    case 2:

      fre_offset_size = SFRAME_FRE_OFFSET_2B;

      break;

    case 4:

      fre_offset_size = SFRAME_FRE_OFFSET_4B;

      break;

    default:

      /* Offset of size 8 bytes is not supported in SFrame format

   version 1.  */

      as_fatal (_("SFrame unsupported offset value\n"));

      break;

    }

  return fre_offset_size;

}

#if SFRAME_FRE_TYPE_SELECTION_OPT

/* Create a composite expression CEXP (for SFrame FRE start address) such that:

      exp = <val> OP_absent <width>, where,

    - <val> and <width> are themselves expressionS.

    - <val> stores the expression which when evaluated gives the value of the

      start address offset of the FRE.

    - <width> stores the expression when evaluated gives the number of bytes

      needed to encode the start address offset of the FRE.

   The use of OP_absent as the X_op_symbol helps identify this expression

   later when fragments are fixed up.  */

static void

create_fre_start_addr_exp (expressionS *cexp, symbolS *fre_pc_begin,

         symbolS *fde_start_address,

         symbolS *fde_end_address)

{

  expressionS val;

  expressionS width;

  /* val expression stores the FDE start address offset from the start PC

     of function.  */

  val.X_op = O_subtract;

  val.X_add_symbol = fre_pc_begin;

  val.X_op_symbol = fde_start_address;

  val.X_add_number = 0;

  /* width expressions stores the size of the function.  This is used later

     to determine the number of bytes to be used to encode the FRE start

     address of each FRE of the function.  */

  width.X_op = O_subtract;

  width.X_add_symbol = fde_end_address;

  width.X_op_symbol = fde_start_address;

  width.X_add_number = 0;

  cexp->X_op = O_absent;

  cexp->X_add_symbol = make_expr_symbol (&val);

  cexp->X_op_symbol = make_expr_symbol (&width);

  cexp->X_add_number = 0;

}

/* Create a composite expression CEXP (for SFrame FDE function info) such that:

      exp = <rest_of_func_info> OP_modulus <width>, where,

    - <rest_of_func_info> and <width> are themselves expressionS.

    - <rest_of_func_info> stores a constant expression where X_add_number is

    used to stash away the func_info.  The upper 4-bits of the func_info are copied

    back to the resulting byte by the fragment fixup logic.

    - <width> stores the expression when evaluated gives the size of the

    function in number of bytes.

   The use of OP_modulus as the X_op_symbol helps identify this expression

   later when fragments are fixed up.  */

static void

create_func_info_exp (expressionS *cexp, symbolS *dw_fde_end_addrS,

          symbolS *dw_fde_start_addrS, uint8_t func_info)

{

  expressionS width;

  expressionS rest_of_func_info;

  width.X_op = O_subtract;

  width.X_add_symbol = dw_fde_end_addrS;

  width.X_op_symbol = dw_fde_start_addrS;

  width.X_add_number = 0;

  rest_of_func_info.X_op = O_constant;

  rest_of_func_info.X_add_number = func_info;

  cexp->X_op = O_modulus;

  cexp->X_add_symbol = make_expr_symbol (&rest_of_func_info);

  cexp->X_op_symbol = make_expr_symbol (&width);

  cexp->X_add_number = 0;

}

#endif

static void

output_sframe_row_entry (symbolS *fde_start_addr,

       symbolS *fde_end_addr,

       struct sframe_row_entry *sframe_fre)

{

  unsigned char fre_info;

  unsigned int fre_num_offsets;

  unsigned int fre_offset_size;

  unsigned int fre_base_reg;

  expressionS exp;

  unsigned int fre_addr_size;

  unsigned int idx = 0;

  unsigned int fre_write_offsets = 0;

  fre_addr_size = 4; /* 4 bytes by default.   FIXME tie it to fre_type? */

  /* SFrame FRE Start Address.  */

#if SFRAME_FRE_TYPE_SELECTION_OPT

  create_fre_start_addr_exp (&exp, sframe_fre->pc_begin, fde_start_addr,

           fde_end_addr);

  frag_grow (fre_addr_size);

  frag_var (rs_sframe, fre_addr_size, 0, (relax_substateT) 0,

      make_expr_symbol (&exp), 0, (char *) frag_now);

#else

  gas_assert (fde_end_addr);

  exp.X_op = O_subtract;

  exp.X_add_symbol = sframe_fre->pc_begin; /* to.  */

  exp.X_op_symbol = fde_start_addr; /* from.  */

  exp.X_add_number = 0;

  emit_expr (&exp, fre_addr_size);

#endif

  /* Create the fre_info using the CFA base register, number of offsets and max

     size of offset in this frame row entry.  */

  fre_base_reg = get_fre_base_reg_id (sframe_fre);

  fre_num_offsets = get_fre_num_offsets (sframe_fre);

  fre_offset_size = sframe_get_fre_offset_size (sframe_fre);

  fre_info = sframe_set_fre_info (fre_base_reg, fre_num_offsets,

          fre_offset_size, sframe_fre->mangled_ra_p);

  out_one (fre_info);

  idx = sframe_fre_offset_func_map_index (fre_offset_size);

  gas_assert (idx < SFRAME_FRE_OFFSET_FUNC_MAP_INDEX_MAX);

  /* Write out the offsets in order - cfa, bp, ra.  */

  fre_offset_func_map[idx].out_func (sframe_fre->cfa_offset);

  fre_write_offsets++;

#ifdef SFRAME_FRE_RA_TRACKING

  if (sframe_fre->ra_loc == SFRAME_FRE_ELEM_LOC_STACK)

    {

      fre_offset_func_map[idx].out_func (sframe_fre->ra_offset);

      fre_write_offsets++;

    }

#endif

  if (sframe_fre->bp_loc == SFRAME_FRE_ELEM_LOC_STACK)

    {

      fre_offset_func_map[idx].out_func (sframe_fre->bp_offset);

      fre_write_offsets++;

    }

  /* Check if the expected number offsets have been written out

     in this FRE.  */

  gas_assert (fre_write_offsets == fre_num_offsets);

}

static void

output_sframe_funcdesc (symbolS *start_of_fre_section,

      symbolS *fre_symbol,

      struct sframe_func_entry *sframe_fde)

{

  expressionS exp;

  unsigned int addr_size;

  symbolS *dw_fde_start_addrS, *dw_fde_end_addrS;

  unsigned int pauth_key;

  addr_size = SFRAME_RELOC_SIZE;

  dw_fde_start_addrS = get_dw_fde_start_addrS (sframe_fde->dw_fde);

  dw_fde_end_addrS = get_dw_fde_end_addrS (sframe_fde->dw_fde);

  /* Start address of the function.  */

  exp.X_op = O_subtract;

  exp.X_add_symbol = dw_fde_start_addrS; /* to location.  */

  exp.X_op_symbol = symbol_temp_new_now (); /* from location.  */

  exp.X_add_number = 0;

  emit_expr (&exp, addr_size);

  /* Size of the function in bytes.  */

  exp.X_op = O_subtract;

  exp.X_add_symbol = dw_fde_end_addrS;

  exp.X_op_symbol = dw_fde_start_addrS;

  exp.X_add_number = 0;

  emit_expr (&exp, addr_size);

  /* Offset to the first frame row entry.  */

  exp.X_op = O_subtract;

  exp.X_add_symbol = fre_symbol; /* Minuend.  */

  exp.X_op_symbol = start_of_fre_section; /* Subtrahend.  */

  exp.X_add_number = 0;

  emit_expr (&exp, addr_size);

  /* Number of FREs.  */

  out_four (sframe_fde->num_fres);

  /* SFrame FDE function info.  */

  unsigned char func_info;

  pauth_key = (get_dw_fde_pauth_b_key_p (sframe_fde->dw_fde)

         ? SFRAME_AARCH64_PAUTH_KEY_B : SFRAME_AARCH64_PAUTH_KEY_A);

  func_info = sframe_set_func_info (SFRAME_FDE_TYPE_PCINC,

            SFRAME_FRE_TYPE_ADDR4,

            pauth_key);

#if SFRAME_FRE_TYPE_SELECTION_OPT

  expressionS cexp;

  create_func_info_exp (&cexp, dw_fde_end_addrS, dw_fde_start_addrS,

      func_info);

  frag_grow (1); /* Size of func info is unsigned char.  */

  frag_var (rs_sframe, 1, 0, (relax_substateT) 0,

      make_expr_symbol (&cexp), 0, (char *) frag_now);

#else

  out_one (func_info);

#endif

  out_one (0);

  out_two (0);

}

static void

output_sframe_internal (void)

{

  expressionS exp;

  unsigned int i = 0;

  symbolS *end_of_frame_hdr;

  symbolS *end_of_frame_section;

  symbolS *start_of_func_desc_section;

  symbolS *start_of_fre_section;

  struct sframe_func_entry *sframe_fde;

  struct sframe_row_entry *sframe_fre;

  unsigned char abi_arch = 0;

  int fixed_fp_offset = SFRAME_CFA_FIXED_FP_INVALID;

  int fixed_ra_offset = SFRAME_CFA_FIXED_RA_INVALID;

  unsigned int addr_size;

  addr_size = SFRAME_RELOC_SIZE;

  /* The function descriptor entries as dumped by the assembler are not

     sorted on PCs.  */

  unsigned char sframe_flags = 0;

  sframe_flags |= !SFRAME_F_FDE_SORTED;

  unsigned int num_fdes = get_num_sframe_fdes ();

  unsigned int num_fres = get_num_sframe_fres ();

  symbolS **fre_symbols = XNEWVEC (symbolS *, num_fres);

  for (i = 0; i < num_fres; i++)

    fre_symbols[i] = symbol_temp_make ();

  end_of_frame_hdr = symbol_temp_make ();

  start_of_fre_section = symbol_temp_make ();

  start_of_func_desc_section = symbol_temp_make ();

  end_of_frame_section = symbol_temp_make ();

  /* Output the preamble of SFrame section.  */

  out_two (SFRAME_MAGIC);

  out_one (SFRAME_VERSION);

  out_one (sframe_flags);

  /* abi/arch.  */

#ifdef sframe_get_abi_arch

  abi_arch = sframe_get_abi_arch ();

#endif

  gas_assert (abi_arch);

  out_one (abi_arch);

  /* Offset for the FP register from CFA.  Neither of the AMD64 or AAPCS64

     ABIs have a fixed offset for the FP register from the CFA.  This may be

     useful in future (but not without additional support in the toolchain)

     for specialized handling/encoding for cases where, for example,

     -fno-omit-frame-pointer is used.  */

  out_one (fixed_fp_offset);

  /* Offset for the return address from CFA is fixed for some ABIs

     (e.g., AMD64), output a SFRAME_CFA_FIXED_RA_INVALID otherwise.  */

#ifdef sframe_ra_tracking_p

  if (!sframe_ra_tracking_p ())

    fixed_ra_offset = sframe_cfa_ra_offset ();

#endif

  out_one (fixed_ra_offset);

  /* None of the AMD64, or AARCH64 ABIs need the auxiliary header.

     When the need does arise to use this field, the appropriate backend

     must provide this information.  */

  out_one (0); /* Auxiliary SFrame header length.  */

  out_four (num_fdes); /* Number of FDEs.  */

  out_four (num_fres); /* Number of FREs.  */

  /* FRE sub-section len.  */

  exp.X_op = O_subtract;

  exp.X_add_symbol = end_of_frame_section;

  exp.X_op_symbol = start_of_fre_section;

  exp.X_add_number = 0;

  emit_expr (&exp, addr_size);

  /* Offset of Function Index sub-section.  */

  exp.X_op = O_subtract;

  exp.X_add_symbol = end_of_frame_hdr;

  exp.X_op_symbol = start_of_func_desc_section;

  exp.X_add_number = 0;

  emit_expr (&exp, addr_size);

  /* Offset of FRE sub-section.  */

  exp.X_op = O_subtract;

  exp.X_add_symbol = start_of_fre_section;

  exp.X_op_symbol = end_of_frame_hdr;

  exp.X_add_number = 0;

  emit_expr (&exp, addr_size);

  symbol_set_value_now (end_of_frame_hdr);

  symbol_set_value_now (start_of_func_desc_section);

  /* Output the SFrame function descriptor entries.  */

  i = 0;

  for (sframe_fde = all_sframe_fdes; sframe_fde; sframe_fde = sframe_fde->next)

    {

      output_sframe_funcdesc (start_of_fre_section,

            fre_symbols[i], sframe_fde);

      i += sframe_fde->num_fres;

    }

  symbol_set_value_now (start_of_fre_section);

  /* Output the SFrame FREs.  */

  i = 0;

  sframe_fde = all_sframe_fdes;

  for (sframe_fde = all_sframe_fdes; sframe_fde; sframe_fde = sframe_fde->next)

    {

      for (sframe_fre = sframe_fde->sframe_fres;

     sframe_fre;

     sframe_fre = sframe_fre->next)

  {

    symbol_set_value_now (fre_symbols[i]);

    output_sframe_row_entry (get_dw_fde_start_addrS (sframe_fde->dw_fde),

           get_dw_fde_end_addrS (sframe_fde->dw_fde),

           sframe_fre);

    i++;

  }

    }

  symbol_set_value_now (end_of_frame_section);

  gas_assert (i == num_fres);

  free (fre_symbols);

  fre_symbols = NULL;

}

/* List of SFrame FDE entries.  */

struct sframe_func_entry *all_sframe_fdes;

/* Tail of the list to add to.  */

static struct sframe_func_entry **last_sframe_fde = &all_sframe_fdes;

static unsigned int

get_num_sframe_fdes (void)

{

  struct sframe_func_entry *sframe_fde;

  unsigned int total_fdes = 0;

  for (sframe_fde = all_sframe_fdes; sframe_fde ; sframe_fde = sframe_fde->next)

    total_fdes++;

  return total_fdes;

}

/* Get the total number of SFrame row entries across the FDEs.  */

static unsigned int

get_num_sframe_fres (void)

{

  struct sframe_func_entry *sframe_fde;

  unsigned int total_fres = 0;

  for (sframe_fde = all_sframe_fdes; sframe_fde ; sframe_fde = sframe_fde->next)

    total_fres += sframe_fde->num_fres;

  return total_fres;

}

/* Allocate an SFrame FDE.  */

static struct sframe_func_entry*

sframe_fde_alloc (void)

{

  struct sframe_func_entry *sframe_fde = XCNEW (struct sframe_func_entry);

  return sframe_fde;

}

/* Link the SFrame FDE in.  */

static int

sframe_fde_link (struct sframe_func_entry *sframe_fde)

{

  *last_sframe_fde = sframe_fde;

  last_sframe_fde = &sframe_fde->next;

  return 0;

}

/* Free up the SFrame FDE.  */

static void

sframe_fde_free (struct sframe_func_entry *sframe_fde)

{

  XDELETE (sframe_fde);

  sframe_fde = NULL;

}

/* SFrame translation context functions.  */

/* Allocate a new SFrame translation context.  */

static struct sframe_xlate_ctx*

sframe_xlate_ctx_alloc (void)

{

  struct sframe_xlate_ctx* xlate_ctx = XCNEW (struct sframe_xlate_ctx);

  return xlate_ctx;

}

/* Initialize the given SFrame translation context.  */

static void

sframe_xlate_ctx_init (struct sframe_xlate_ctx *xlate_ctx)

{

  xlate_ctx->dw_fde = NULL;

  xlate_ctx->first_fre = NULL;

  xlate_ctx->last_fre = NULL;

  xlate_ctx->cur_fre = NULL;

  xlate_ctx->remember_fre = NULL;

  xlate_ctx->num_xlate_fres = 0;

}

/* Cleanup the given SFrame translation context.  */

static void

sframe_xlate_ctx_cleanup (struct sframe_xlate_ctx *xlate_ctx)

{

  struct sframe_row_entry *fre, *fre_next;

  if (xlate_ctx->num_xlate_fres)

    {

      fre = xlate_ctx->first_fre;

      while (fre)

  {

    fre_next = fre->next;

    XDELETE (fre);

    fre = fre_next;

  }

    }

  XDELETE (xlate_ctx->cur_fre);

  sframe_xlate_ctx_init (xlate_ctx);

}

/* Transfer the state from the SFrame translation context to the SFrame FDE.  */

static void

sframe_xlate_ctx_finalize (struct sframe_xlate_ctx *xlate_ctx,

         struct sframe_func_entry *sframe_fde)

{

  sframe_fde->dw_fde = xlate_ctx->dw_fde;

  sframe_fde->sframe_fres = xlate_ctx->first_fre;

  sframe_fde->num_fres = xlate_ctx->num_xlate_fres;

}

static struct sframe_row_entry*

sframe_row_entry_new (void)

{

  struct sframe_row_entry *fre = XCNEW (struct sframe_row_entry);

  /* Reset cfa_base_reg to -1.  A value of 0 will imply some valid register

     for the supported arches.  */

  fre->cfa_base_reg = -1;

  fre->merge_candidate = true;

  /* Reset the mangled RA status bit to zero by default.  We will initialize it in

     sframe_row_entry_initialize () with the sticky bit if set.  */

  fre->mangled_ra_p = false;

  return fre;

}

/* Add the given FRE in the list of frame row entries in the given FDE

   translation context.  */

static void

sframe_xlate_ctx_add_fre (struct sframe_xlate_ctx *xlate_ctx,

       struct sframe_row_entry *fre)

{

  gas_assert (xlate_ctx && fre);

  /* Add the frame row entry.  */

  if (!xlate_ctx->first_fre)

    xlate_ctx->first_fre = fre;

  else if (xlate_ctx->last_fre)

    xlate_ctx->last_fre->next = fre;

  xlate_ctx->last_fre = fre;

  /* Keep track of the total number of SFrame frame row entries.  */

  xlate_ctx->num_xlate_fres++;

}

/* A SFrame Frame Row Entry is self-sufficient in terms of stack tracing info

   for a given PC.  It contains information assimilated from multiple CFI

   instructions, and hence, a new SFrame FRE is initialized with the data from

   the previous known FRE, if any.

   Understandably, not all information (especially the instruction begin

   and end boundaries) needs to be relayed.  Hence, the caller of this API

   must set the pc_begin and pc_end as applicable.  */

static void

sframe_row_entry_initialize (struct sframe_row_entry *cur_fre,

           struct sframe_row_entry *prev_fre)

{

  gas_assert (prev_fre);

  cur_fre->cfa_base_reg = prev_fre->cfa_base_reg;

  cur_fre->cfa_offset = prev_fre->cfa_offset;

  cur_fre->bp_loc = prev_fre->bp_loc;

  cur_fre->bp_offset = prev_fre->bp_offset;

  cur_fre->ra_loc = prev_fre->ra_loc;

  cur_fre->ra_offset = prev_fre->ra_offset;

  /* Treat RA mangling as a sticky bit.  It retains its value until another

     .cfi_negate_ra_state is seen.  */

  cur_fre->mangled_ra_p = prev_fre->mangled_ra_p;

}

/* Translate DW_CFA_advance_loc into SFrame context.

   Return SFRAME_XLATE_OK if success.  */

static int

sframe_xlate_do_advance_loc (struct sframe_xlate_ctx *xlate_ctx,

           struct cfi_insn_data *cfi_insn)

{

  struct sframe_row_entry *last_fre = xlate_ctx->last_fre;

  /* Get the scratchpad FRE currently being updated as the cfi_insn's

     get interpreted.  This FRE eventually gets linked in into the

     list of FREs for the specific function.  */

  struct sframe_row_entry *cur_fre = xlate_ctx->cur_fre;

  if (cur_fre)

    {

      if (!cur_fre->merge_candidate)

  {

    sframe_fre_set_end_addr (cur_fre, cfi_insn->u.ll.lab2);

    sframe_xlate_ctx_add_fre (xlate_ctx, cur_fre);

    last_fre = xlate_ctx->last_fre;

    xlate_ctx->cur_fre = sframe_row_entry_new ();

    cur_fre = xlate_ctx->cur_fre;

    if (last_fre)

      sframe_row_entry_initialize (cur_fre, last_fre);

  }

      else

  {

    sframe_fre_set_end_addr (last_fre, cfi_insn->u.ll.lab2);

    gas_assert (last_fre->merge_candidate == false);

  }

    }

  else

    {

      xlate_ctx->cur_fre = sframe_row_entry_new ();

      cur_fre = xlate_ctx->cur_fre;

    }