/* Find debugging and symbol information for a module in libdwfl.

   Copyright (C) 2005-2012, 2014, 2015 Red Hat, Inc.

   This file is part of elfutils.

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

   it under the terms of either

     * the GNU Lesser General Public License as published by the Free

       Software Foundation; either version 3 of the License, or (at

       your option) any later version

   or

     * the GNU General Public License as published by the Free

       Software Foundation; either version 2 of the License, or (at

       your option) any later version

   or both in parallel, as here.

   elfutils 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 copies of the GNU General Public License and

   the GNU Lesser General Public License along with this program.  If

   not, see <http://www.gnu.org/licenses/>.  */

#ifdef HAVE_CONFIG_H

# include <config.h>

#endif

#include "libdwflP.h"

#include <inttypes.h>

#include <fcntl.h>

#include <string.h>

#include <unistd.h>

#include "../libdw/libdwP.h"	/* DWARF_E_* values are here.  */

#include "../libelf/libelfP.h"

#include "system.h"

static inline Dwfl_Error

open_elf_file (Elf **elf, int *fd, char **name)

{

  if (*elf == NULL)

    {

      /* CBFAIL uses errno if it's set, so clear it first in case we don't

	 set it with an open failure below.  */

      errno = 0;

      /* If there was a pre-primed file name left that the callback left

	 behind, try to open that file name.  */

      if (*fd < 0 && *name != NULL)

	*fd = TEMP_FAILURE_RETRY (open (*name, O_RDONLY));

      if (*fd < 0)

	return CBFAIL;

      return __libdw_open_file (fd, elf, true, false);

    }

  else if (unlikely (elf_kind (*elf) != ELF_K_ELF))

    {

      elf_end (*elf);

      *elf = NULL;

      close (*fd);

      *fd = -1;

      return DWFL_E_BADELF;

    }

  /* Elf file already open and looks fine.  */

  return DWFL_E_NOERROR;

}

/* Open libelf FILE->fd and compute the load base of ELF as loaded in MOD.

   When we return success, FILE->elf and FILE->vaddr are set up.  */

static inline Dwfl_Error

open_elf (Dwfl_Module *mod, struct dwfl_file *file)

{

  Dwfl_Error error = open_elf_file (&file->elf, &file->fd, &file->name);

  if (error != DWFL_E_NOERROR)

    return error;

  GElf_Ehdr ehdr_mem, *ehdr = gelf_getehdr (file->elf, &ehdr_mem);

  if (ehdr == NULL)

    {

    elf_error:

      elf_end (file->elf);

      file->elf = NULL;

      close (file->fd);

      file->fd = -1;

      return DWFL_E (LIBELF, elf_errno ());

    }

  if (ehdr->e_type != ET_REL)

    {

      /* In any non-ET_REL file, we compute the "synchronization address".

	 We start with the address at the end of the first PT_LOAD

	 segment.  When prelink converts REL to RELA in an ET_DYN

	 file, it expands the space between the beginning of the

	 segment and the actual code/data addresses.  Since that

	 change wasn't made in the debug file, the distance from

	 p_vaddr to an address of interest (in an st_value or DWARF

	 data) now differs between the main and debug files.  The

	 distance from address_sync to an address of interest remains

	 consistent.

	 If there are no section headers at all (full stripping), then

	 the end of the first segment is a valid synchronization address.

	 This cannot happen in a prelinked file, since prelink itself

	 relies on section headers for prelinking and for undoing it.

	 (If you do full stripping on a prelinked file, then you get what

	 you deserve--you can neither undo the prelinking, nor expect to

	 line it up with a debug file separated before prelinking.)

	 However, when prelink processes an ET_EXEC file, it can do

	 something different.  There it juggles the "special" sections

	 (SHT_DYNSYM et al) to make space for the additional prelink

	 special sections.  Sometimes it will do this by moving a special

	 section like .dynstr after the real program sections in the first

	 PT_LOAD segment--i.e. to the end.  That changes the end address of

	 the segment, so it no longer lines up correctly and is not a valid

	 synchronization address to use.  Because of this, we need to apply

	 a different prelink-savvy means to discover the synchronization

	 address when there is a separate debug file and a prelinked main

	 file.  That is done in find_debuginfo, below.  */

      size_t phnum;

      if (unlikely (elf_getphdrnum (file->elf, &phnum) != 0))

	goto elf_error;

      file->vaddr = file->address_sync = 0;

      for (size_t i = 0; i < phnum; ++i)

	{

	  GElf_Phdr ph_mem;

	  GElf_Phdr *ph = gelf_getphdr (file->elf, i, &ph_mem);

	  if (unlikely (ph == NULL))

	    goto elf_error;

	  if (ph->p_type == PT_LOAD)

	    {

	      file->vaddr = ph->p_vaddr & -ph->p_align;

	      file->address_sync = ph->p_vaddr + ph->p_memsz;

	      break;

	    }

	}

    }

  /* We only want to set the module e_type explictly once, derived from

     the main ELF file.  (It might be changed for the kernel, because

     that is special - see below.)  open_elf is always called first for

     the main ELF file, because both find_dw and find_symtab call

     __libdwfl_getelf first to open the main file.  So don't let debug

     or aux files override the module e_type.  The kernel heuristic

     below could otherwise trigger for non-kernel/non-main files, since

     their phdrs might not match the actual load addresses.  */

  if (file == &mod->main)

    {

      mod->e_type = ehdr->e_type;

      /* Relocatable Linux kernels are ET_EXEC but act like ET_DYN.  */

      if (mod->e_type == ET_EXEC && file->vaddr != mod->low_addr)

	mod->e_type = ET_DYN;

    }

  else

    assert (mod->main.elf != NULL);

  return DWFL_E_NOERROR;

}

/* We have an authoritative build ID for this module MOD, so don't use

   a file by name that doesn't match that ID.  */

static void

mod_verify_build_id (Dwfl_Module *mod)

{

  assert (mod->build_id_len > 0);

  switch (__builtin_expect (__libdwfl_find_build_id (mod, false,

						     mod->main.elf), 2))

    {

    case 2:

      /* Build ID matches as it should. */

      return;

    case -1:			/* ELF error.  */

      mod->elferr = INTUSE(dwfl_errno) ();

      break;

    case 0:			/* File has no build ID note.  */

    case 1:			/* FIle has a build ID that does not match.  */

      mod->elferr = DWFL_E_WRONG_ID_ELF;

      break;

    default:

      abort ();

    }

  /* We get here when it was the right ELF file.  Clear it out.  */

  elf_end (mod->main.elf);

  mod->main.elf = NULL;

  if (mod->main.fd >= 0)

    {

      close (mod->main.fd);

      mod->main.fd = -1;

    }

}

/* Find the main ELF file for this module and open libelf on it.

   When we return success, MOD->main.elf and MOD->main.bias are set up.  */

void

internal_function

__libdwfl_getelf (Dwfl_Module *mod)

{

  if (mod->main.elf != NULL	/* Already done.  */

      || mod->elferr != DWFL_E_NOERROR)	/* Cached failure.  */

    return;

  mod->main.fd = (*mod->dwfl->callbacks->find_elf) (MODCB_ARGS (mod),

						    &mod->main.name,

						    &mod->main.elf);

  const bool fallback = mod->main.elf == NULL && mod->main.fd < 0;

  mod->elferr = open_elf (mod, &mod->main);

  if (mod->elferr != DWFL_E_NOERROR)

    return;

  if (!mod->main.valid)

    {

      /* Clear any explicitly reported build ID, just in case it was wrong.

	 We'll fetch it from the file when asked.  */

      free (mod->build_id_bits);

      mod->build_id_bits = NULL;

      mod->build_id_len = 0;

    }

  else if (fallback)

    mod_verify_build_id (mod);

  mod->main_bias = mod->e_type == ET_REL ? 0 : mod->low_addr - mod->main.vaddr;

}

static inline void

consider_shdr (GElf_Addr interp,

               GElf_Word sh_type,

               GElf_Xword sh_flags,

               GElf_Addr sh_addr,

               GElf_Xword sh_size,

               GElf_Addr *phighest)

{

  if ((sh_flags & SHF_ALLOC)

      && ((sh_type == SHT_PROGBITS && sh_addr != interp)

          || sh_type == SHT_NOBITS))

    {

      const GElf_Addr sh_end = sh_addr + sh_size;

      if (sh_end > *phighest)

        *phighest = sh_end;

    }

}

/* If the main file might have been prelinked, then we need to

   discover the correct synchronization address between the main and

   debug files.  Because of prelink's section juggling, we cannot rely

   on the address_sync computed from PT_LOAD segments (see open_elf).

   We will attempt to discover a synchronization address based on the

   section headers instead.  But finding a section address that is

   safe to use requires identifying which sections are SHT_PROGBITS.

   We can do that in the main file, but in the debug file all the

   allocated sections have been transformed into SHT_NOBITS so we have

   lost the means to match them up correctly.

   The only method left to us is to decode the .gnu.prelink_undo

   section in the prelinked main file.  This shows what the sections

   looked like before prelink juggled them--when they still had a

   direct correspondence to the debug file.  */

static Dwfl_Error

find_prelink_address_sync (Dwfl_Module *mod, struct dwfl_file *file)

{

  /* The magic section is only identified by name.  */

  size_t shstrndx;

  if (elf_getshdrstrndx (mod->main.elf, &shstrndx) < 0)

    return DWFL_E_LIBELF;

  Elf_Scn *scn = NULL;

  while ((scn = elf_nextscn (mod->main.elf, scn)) != NULL)

    {

      GElf_Shdr shdr_mem;

      GElf_Shdr *shdr = gelf_getshdr (scn, &shdr_mem);

      if (unlikely (shdr == NULL))

	return DWFL_E_LIBELF;

      if (shdr->sh_type == SHT_PROGBITS

	  && !(shdr->sh_flags & SHF_ALLOC)

	  && shdr->sh_name != 0)

	{

	  const char *secname = elf_strptr (mod->main.elf, shstrndx,

					    shdr->sh_name);

	  if (unlikely (secname == NULL))

	    return DWFL_E_LIBELF;

	  if (!strcmp (secname, ".gnu.prelink_undo"))

	    break;

	}

    }

  if (scn == NULL)

    /* There was no .gnu.prelink_undo section.  */

    return DWFL_E_NOERROR;

  Elf_Data *undodata = elf_rawdata (scn, NULL);

  if (unlikely (undodata == NULL))

    return DWFL_E_LIBELF;

  /* Decode the section.  It consists of the original ehdr, phdrs,

     and shdrs (but omits section 0).  */

  union

  {

    Elf32_Ehdr e32;

    Elf64_Ehdr e64;

  } ehdr;

  Elf_Data dst =

    {

      .d_buf = &ehdr,

      .d_size = sizeof ehdr,

      .d_type = ELF_T_EHDR,

      .d_version = EV_CURRENT

    };

  Elf_Data src = *undodata;

  src.d_size = gelf_fsize (mod->main.elf, ELF_T_EHDR, 1, EV_CURRENT);

  src.d_type = ELF_T_EHDR;

  if (unlikely (gelf_xlatetom (mod->main.elf, &dst, &src,

			       elf_getident (mod->main.elf, NULL)[EI_DATA])

		== NULL))

    return DWFL_E_LIBELF;

  size_t shentsize = gelf_fsize (mod->main.elf, ELF_T_SHDR, 1, EV_CURRENT);

  size_t phentsize = gelf_fsize (mod->main.elf, ELF_T_PHDR, 1, EV_CURRENT);

  uint_fast16_t phnum;

  uint_fast16_t shnum;

  if (ehdr.e32.e_ident[EI_CLASS] == ELFCLASS32)

    {

      if (ehdr.e32.e_shentsize != shentsize

	  || ehdr.e32.e_phentsize != phentsize)

	return DWFL_E_BAD_PRELINK;

      phnum = ehdr.e32.e_phnum;

      shnum = ehdr.e32.e_shnum;

    }

  else

    {

      if (ehdr.e64.e_shentsize != shentsize

	  || ehdr.e64.e_phentsize != phentsize)

	return DWFL_E_BAD_PRELINK;

      phnum = ehdr.e64.e_phnum;

      shnum = ehdr.e64.e_shnum;

    }

  /* Since prelink does not store the zeroth section header in the undo

     section, it cannot support SHN_XINDEX encoding.  */

  if (unlikely (shnum >= SHN_LORESERVE) || unlikely(shnum == 0)

      || unlikely (undodata->d_size != (src.d_size

					+ phnum * phentsize

					+ (shnum - 1) * shentsize)))

    return DWFL_E_BAD_PRELINK;

  --shnum;

  /* We look at the allocated SHT_PROGBITS (or SHT_NOBITS) sections.  (Most

     every file will have some SHT_PROGBITS sections, but it's possible to

     have one with nothing but .bss, i.e. SHT_NOBITS.)  The special sections

     that can be moved around have different sh_type values--except for

     .interp, the section that became the PT_INTERP segment.  So we exclude

     the SHT_PROGBITS section whose address matches the PT_INTERP p_vaddr.

     For this reason, we must examine the phdrs first to find PT_INTERP.  */

  GElf_Addr main_interp = 0;

  {

    size_t main_phnum;

    if (unlikely (elf_getphdrnum (mod->main.elf, &main_phnum)))

      return DWFL_E_LIBELF;

    for (size_t i = 0; i < main_phnum; ++i)

      {

	GElf_Phdr phdr;

	if (unlikely (gelf_getphdr (mod->main.elf, i, &phdr) == NULL))

	  return DWFL_E_LIBELF;

	if (phdr.p_type == PT_INTERP)

	  {

	    main_interp = phdr.p_vaddr;

	    break;

	  }

      }

  }

  src.d_buf += src.d_size;

  src.d_type = ELF_T_PHDR;

  src.d_size = phnum * phentsize;

  GElf_Addr undo_interp = 0;

  bool class32 = ehdr.e32.e_ident[EI_CLASS] == ELFCLASS32;

  {

    size_t phdr_size = class32 ? sizeof (Elf32_Phdr) : sizeof (Elf64_Phdr);

    if (unlikely (phnum > SIZE_MAX / phdr_size))

      return DWFL_E_NOMEM;

    const size_t phdrs_bytes = phnum * phdr_size;

    void *phdrs = malloc (phdrs_bytes);

    if (unlikely (phdrs == NULL))

      return DWFL_E_NOMEM;

    dst.d_buf = phdrs;

    dst.d_size = phdrs_bytes;

    if (unlikely (gelf_xlatetom (mod->main.elf, &dst, &src,

				 ehdr.e32.e_ident[EI_DATA]) == NULL))

      {

	free (phdrs);

	return DWFL_E_LIBELF;

      }

    if (class32)

      {

	Elf32_Phdr (*p32)[phnum] = phdrs;

	for (uint_fast16_t i = 0; i < phnum; ++i)

	  if ((*p32)[i].p_type == PT_INTERP)

	    {

	      undo_interp = (*p32)[i].p_vaddr;

	      break;

	    }

      }

    else

      {

	Elf64_Phdr (*p64)[phnum] = phdrs;

	for (uint_fast16_t i = 0; i < phnum; ++i)

	  if ((*p64)[i].p_type == PT_INTERP)

	    {

	      undo_interp = (*p64)[i].p_vaddr;

	      break;

	    }

      }

    free (phdrs);

  }

  if (unlikely ((main_interp == 0) != (undo_interp == 0)))

    return DWFL_E_BAD_PRELINK;

  src.d_buf += src.d_size;

  src.d_type = ELF_T_SHDR;

  src.d_size = gelf_fsize (mod->main.elf, ELF_T_SHDR, shnum, EV_CURRENT);

  size_t shdr_size = class32 ? sizeof (Elf32_Shdr) : sizeof (Elf64_Shdr);

  if (unlikely (shnum > SIZE_MAX / shdr_size))

    return DWFL_E_NOMEM;

  const size_t shdrs_bytes = shnum * shdr_size;

  void *shdrs = malloc (shdrs_bytes);

  if (unlikely (shdrs == NULL))

    return DWFL_E_NOMEM;

  dst.d_buf = shdrs;

  dst.d_size = shdrs_bytes;

  if (unlikely (gelf_xlatetom (mod->main.elf, &dst, &src,

			       ehdr.e32.e_ident[EI_DATA]) == NULL))

    {

      free (shdrs);

      return DWFL_E_LIBELF;

    }

  /* Now we can look at the original section headers of the main file

     before it was prelinked.  First we'll apply our method to the main

     file sections as they are after prelinking, to calculate the

     synchronization address of the main file.  Then we'll apply that

     same method to the saved section headers, to calculate the matching

     synchronization address of the debug file.

     The method is to consider SHF_ALLOC sections that are either

     SHT_PROGBITS or SHT_NOBITS, excluding the section whose sh_addr

     matches the PT_INTERP p_vaddr.  The special sections that can be

     moved by prelink have other types, except for .interp (which

     becomes PT_INTERP).  The "real" sections cannot move as such, but

     .bss can be split into .dynbss and .bss, with the total memory

     image remaining the same but being spread across the two sections.

     So we consider the highest section end, which still matches up.  */

  GElf_Addr highest;

  highest = 0;

  scn = NULL;

  while ((scn = elf_nextscn (mod->main.elf, scn)) != NULL)

    {

      GElf_Shdr sh_mem;

      GElf_Shdr *sh = gelf_getshdr (scn, &sh_mem);

      if (unlikely (sh == NULL))

	{

	  free (shdrs);

	  return DWFL_E_LIBELF;

	}

      consider_shdr (main_interp, sh->sh_type, sh->sh_flags,

		     sh->sh_addr, sh->sh_size, &highest);

    }

  if (highest > mod->main.vaddr)

    {

      mod->main.address_sync = highest;

      highest = 0;

      if (class32)

	{

	  Elf32_Shdr (*s32)[shnum] = shdrs;

	  for (size_t i = 0; i < shnum; ++i)

	    consider_shdr (undo_interp, (*s32)[i].sh_type,

			   (*s32)[i].sh_flags, (*s32)[i].sh_addr,

			   (*s32)[i].sh_size, &highest);

	}

      else

	{

	  Elf64_Shdr (*s64)[shnum] = shdrs;

	  for (size_t i = 0; i < shnum; ++i)

	    consider_shdr (undo_interp, (*s64)[i].sh_type,

			   (*s64)[i].sh_flags, (*s64)[i].sh_addr,

			   (*s64)[i].sh_size, &highest);

	}

      if (highest > file->vaddr)

	file->address_sync = highest;

      else

	{

	  free (shdrs);

	  return DWFL_E_BAD_PRELINK;

	}

    }

  free (shdrs);

  return DWFL_E_NOERROR;

}

/* Find the separate debuginfo file for this module and open libelf on it.

   When we return success, MOD->debug is set up.  */

static Dwfl_Error

find_debuginfo (Dwfl_Module *mod)

{

  if (mod->debug.elf != NULL)

    return DWFL_E_NOERROR;

  GElf_Word debuglink_crc = 0;

  const char *debuglink_file;

  debuglink_file = INTUSE(dwelf_elf_gnu_debuglink) (mod->main.elf,

						    &debuglink_crc);

  mod->debug.fd = (*mod->dwfl->callbacks->find_debuginfo) (MODCB_ARGS (mod),

							   mod->main.name,

							   debuglink_file,

							   debuglink_crc,

							   &mod->debug.name);

  Dwfl_Error result = open_elf (mod, &mod->debug);

  if (result == DWFL_E_NOERROR && mod->debug.address_sync != 0)

    result = find_prelink_address_sync (mod, &mod->debug);

  return result;

}

/* Try to find the alternative debug link for the given DWARF and set

   it if found.  Only called when mod->dw is already setup but still

   might need an alternative (dwz multi) debug file.  filename is either

   the main or debug name from which the Dwarf was created. */

static void

find_debug_altlink (Dwfl_Module *mod, const char *filename)

{

  assert (mod->dw != NULL);

  const char *altname;

  const void *build_id;

  ssize_t build_id_len = INTUSE(dwelf_dwarf_gnu_debugaltlink) (mod->dw,

							       &altname,

							       &build_id);

  if (build_id_len > 0)

    {

      /* We could store altfile in the module, but don't really need it.  */

      char *altfile = NULL;

      mod->alt_fd = (*mod->dwfl->callbacks->find_debuginfo) (MODCB_ARGS (mod),

							     filename,

							     altname,

							     0,

							     &altfile);

      /* The (internal) callbacks might just set mod->alt_elf directly

	 because they open the Elf anyway for sanity checking.

	 Otherwise open either the given file name or use the fd

	 returned.  */

      Dwfl_Error error = open_elf_file (&mod->alt_elf, &mod->alt_fd,

					&altfile);

      if (error == DWFL_E_NOERROR)

	{

	  mod->alt = INTUSE(dwarf_begin_elf) (mod->alt_elf,

					      DWARF_C_READ, NULL);

	  if (mod->alt == NULL)

	    {

	      elf_end (mod->alt_elf);

	      mod->alt_elf = NULL;

	      close (mod->alt_fd);

	      mod->alt_fd = -1;

	    }

	  else

	    dwarf_setalt (mod->dw, mod->alt);

	}

      free (altfile); /* See above, we don't really need it.  */

    }

}

/* Try to find a symbol table in FILE.

   Returns DWFL_E_NOERROR if a proper one is found.

   Returns DWFL_E_NO_SYMTAB if not, but still sets results for SHT_DYNSYM.  */

static Dwfl_Error

load_symtab (struct dwfl_file *file, struct dwfl_file **symfile,

	     Elf_Scn **symscn, Elf_Scn **xndxscn,

	     size_t *syments, int *first_global, GElf_Word *strshndx)

{

  bool symtab = false;

  Elf_Scn *scn = NULL;

  while ((scn = elf_nextscn (file->elf, scn)) != NULL)

    {

      GElf_Shdr shdr_mem, *shdr = gelf_getshdr (scn, &shdr_mem);

      if (shdr != NULL)

	switch (shdr->sh_type)

	  {

	  case SHT_SYMTAB:

	    if (shdr->sh_entsize == 0)

	      break;

	    symtab = true;

	    *symscn = scn;

	    *symfile = file;

	    *strshndx = shdr->sh_link;

	    *syments = shdr->sh_size / shdr->sh_entsize;

	    *first_global = shdr->sh_info;

	    if (*xndxscn != NULL)

	      return DWFL_E_NOERROR;

	    break;

	  case SHT_DYNSYM:

	    if (symtab)

	      break;

	    /* Use this if need be, but keep looking for SHT_SYMTAB.  */

	    if (shdr->sh_entsize == 0)

	      break;

	    *symscn = scn;

	    *symfile = file;

	    *strshndx = shdr->sh_link;

	    *syments = shdr->sh_size / shdr->sh_entsize;

	    *first_global = shdr->sh_info;

	    break;

	  case SHT_SYMTAB_SHNDX:

	    *xndxscn = scn;

	    if (symtab)

	      return DWFL_E_NOERROR;

	    break;

	  default:

	    break;

	  }

    }

  if (symtab)

    /* We found one, though no SHT_SYMTAB_SHNDX to go with it.  */

    return DWFL_E_NOERROR;

  /* We found no SHT_SYMTAB, so any SHT_SYMTAB_SHNDX was bogus.

     We might have found an SHT_DYNSYM and set *SYMSCN et al though.  */

  *xndxscn = NULL;

  return DWFL_E_NO_SYMTAB;

}

/* Translate addresses into file offsets.

   OFFS[*] start out zero and remain zero if unresolved.  */

static void

find_offsets (Elf *elf, GElf_Addr main_bias, size_t phnum, size_t n,

	      GElf_Addr addrs[n], GElf_Off offs[n])

{

  size_t unsolved = n;

  for (size_t i = 0; i < phnum; ++i)

    {

      GElf_Phdr phdr_mem;

      GElf_Phdr *phdr = gelf_getphdr (elf, i, &phdr_mem);

      if (phdr != NULL && phdr->p_type == PT_LOAD && phdr->p_memsz > 0)

	for (size_t j = 0; j < n; ++j)

	  if (offs[j] == 0

	      && addrs[j] >= phdr->p_vaddr + main_bias

	      && addrs[j] - (phdr->p_vaddr + main_bias) < phdr->p_filesz)

	    {

	      offs[j] = addrs[j] - (phdr->p_vaddr + main_bias) + phdr->p_offset;

	      if (--unsolved == 0)

		break;

	    }

    }

}

/* Various addresses we might want to pull from the dynamic segment.  */

enum

{

  i_symtab,

  i_strtab,

  i_hash,

  i_gnu_hash,

  i_max

};

/* Translate pointers into file offsets.  ADJUST is either zero

   in case the dynamic segment wasn't adjusted or mod->main_bias.

   Will set mod->symfile if the translated offsets can be used as

   symbol table.  */

static void

translate_offs (GElf_Addr adjust,

                Dwfl_Module *mod, size_t phnum,

                GElf_Addr addrs[i_max], GElf_Xword strsz,

                GElf_Ehdr *ehdr)

{

  GElf_Off offs[i_max] = { 0, };

  find_offsets (mod->main.elf, adjust, phnum, i_max, addrs, offs);

  /* Figure out the size of the symbol table.  */

  if (offs[i_hash] != 0)

    {

      /* In the original format, .hash says the size of .dynsym.  */

      size_t entsz = SH_ENTSIZE_HASH (ehdr);

      Elf_Data *data = elf_getdata_rawchunk (mod->main.elf,

					     offs[i_hash] + entsz, entsz,

					     (entsz == 4

					      ? ELF_T_WORD : ELF_T_XWORD));

      if (data != NULL)

	mod->syments = (entsz == 4

			? *(const GElf_Word *) data->d_buf

			: *(const GElf_Xword *) data->d_buf);

    }

  if (offs[i_gnu_hash] != 0 && mod->syments == 0)

    {

      /* In the new format, we can derive it with some work.  */

      const struct

      {

        Elf32_Word nbuckets;

        Elf32_Word symndx;

        Elf32_Word maskwords;

        Elf32_Word shift2;

      } *header;

      Elf_Data *data = elf_getdata_rawchunk (mod->main.elf, offs[i_gnu_hash],

					     sizeof *header, ELF_T_WORD);

      if (data != NULL)

        {

          header = data->d_buf;

          Elf32_Word nbuckets = header->nbuckets;

          Elf32_Word symndx = header->symndx;

          GElf_Off buckets_at = (offs[i_gnu_hash] + sizeof *header

				 + (gelf_getclass (mod->main.elf)

				    * sizeof (Elf32_Word)

				    * header->maskwords));

          // elf_getdata_rawchunk takes a size_t, make sure it

          // doesn't overflow.

#if SIZE_MAX <= UINT32_MAX

          if (nbuckets > SIZE_MAX / sizeof (Elf32_Word))

            data = NULL;

          else

#endif

            data = elf_getdata_rawchunk (mod->main.elf, buckets_at,

					   nbuckets * sizeof (Elf32_Word),

					   ELF_T_WORD);

	  if (data != NULL && symndx < nbuckets)

	    {

	      const Elf32_Word *const buckets = data->d_buf;

	      Elf32_Word maxndx = symndx;

	      for (Elf32_Word bucket = 0; bucket < nbuckets; ++bucket)

		if (buckets[bucket] > maxndx)

		  maxndx = buckets[bucket];

	      GElf_Off hasharr_at = (buckets_at

				     + nbuckets * sizeof (Elf32_Word));

	      hasharr_at += (maxndx - symndx) * sizeof (Elf32_Word);

	      do

		{

		  data = elf_getdata_rawchunk (mod->main.elf,

					       hasharr_at,

					       sizeof (Elf32_Word),

					       ELF_T_WORD);

		  if (data != NULL

		      && (*(const Elf32_Word *) data->d_buf & 1u))

		    {

		      mod->syments = maxndx + 1;

		      break;

		    }

		  ++maxndx;

		  hasharr_at += sizeof (Elf32_Word);

		}

	      while (data != NULL);

	    }

	}

    }

  if (offs[i_strtab] > offs[i_symtab] && mod->syments == 0)

    mod->syments = ((offs[i_strtab] - offs[i_symtab])

		    / gelf_fsize (mod->main.elf,

				  ELF_T_SYM, 1, EV_CURRENT));

  if (mod->syments > 0)

    {

      mod->symdata = elf_getdata_rawchunk (mod->main.elf,

					   offs[i_symtab],

					   gelf_fsize (mod->main.elf,

						       ELF_T_SYM,

						       mod->syments,

						       EV_CURRENT),

						       ELF_T_SYM);

      if (mod->symdata != NULL)

	{

	  mod->symstrdata = elf_getdata_rawchunk (mod->main.elf,

						  offs[i_strtab],

						  strsz,

						  ELF_T_BYTE);

	  if (mod->symstrdata == NULL)

	    mod->symdata = NULL;

	}

      if (mod->symdata == NULL)

	mod->symerr = DWFL_E (LIBELF, elf_errno ());

      else

	{

	  mod->symfile = &mod->main;

	  mod->symerr = DWFL_E_NOERROR;

	}

    }

}

/* Try to find a dynamic symbol table via phdrs.  */

static void

find_dynsym (Dwfl_Module *mod)

{

  GElf_Ehdr ehdr_mem;

  GElf_Ehdr *ehdr = gelf_getehdr (mod->main.elf, &ehdr_mem);

  size_t phnum;

  if (unlikely (elf_getphdrnum (mod->main.elf, &phnum) != 0))

    return;

  for (size_t i = 0; i < phnum; ++i)

    {

      GElf_Phdr phdr_mem;

      GElf_Phdr *phdr = gelf_getphdr (mod->main.elf, i, &phdr_mem);

      if (phdr == NULL)

	break;

      if (phdr->p_type == PT_DYNAMIC)

	{

	  /* Examine the dynamic section for the pointers we need.  */

	  Elf_Data *data = elf_getdata_rawchunk (mod->main.elf,

						 phdr->p_offset, phdr->p_filesz,

						 ELF_T_DYN);

	  if (data == NULL)

	    continue;

	  GElf_Addr addrs[i_max] = { 0, };

	  GElf_Xword strsz = 0;

	  size_t n = data->d_size / gelf_fsize (mod->main.elf,

						ELF_T_DYN, 1, EV_CURRENT);

	  for (size_t j = 0; j < n; ++j)

	    {

	      GElf_Dyn dyn_mem;

	      GElf_Dyn *dyn = gelf_getdyn (data, j, &dyn_mem);

	      if (dyn != NULL)

		switch (dyn->d_tag)

		  {

		  case DT_SYMTAB:

		    addrs[i_symtab] = dyn->d_un.d_ptr;

		    continue;

		  case DT_HASH:

		    addrs[i_hash] = dyn->d_un.d_ptr;

		    continue;

		  case DT_GNU_HASH:

		    addrs[i_gnu_hash] = dyn->d_un.d_ptr;

		    continue;

		  case DT_STRTAB:

		    addrs[i_strtab] = dyn->d_un.d_ptr;

		    continue;

		  case DT_STRSZ:

		    strsz = dyn->d_un.d_val;

		    continue;