xref: /third_party/elfutils/libdwfl/link_map.c (revision da0c48c4)

/* Report modules by examining dynamic linker data structures.
   Copyright (C) 2008-2016 Red Hat, Inc.
   Copyright (C) 2021 Mark J. Wielaard <mark@klomp.org>
   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/>.  */

#include <config.h>
#include "libdwflP.h"
#include "../libdw/memory-access.h"
#include "system.h"

#include <fcntl.h>

/* This element is always provided and always has a constant value.
   This makes it an easy thing to scan for to discern the format.  */
#define PROBE_TYPE	AT_PHENT
#define PROBE_VAL32	sizeof (Elf32_Phdr)
#define PROBE_VAL64	sizeof (Elf64_Phdr)


static inline bool
do_check64 (const char *a64, uint_fast8_t *elfdata)
{
  /* The AUXV pointer might not even be naturally aligned for 64-bit
     data, because note payloads in a core file are not aligned.  */
  const char *typep = a64 + offsetof (Elf64_auxv_t, a_type);
  uint64_t type = read_8ubyte_unaligned_noncvt (typep);
  const char *valp = a64 + offsetof (Elf64_auxv_t, a_un.a_val);
  uint64_t val = read_8ubyte_unaligned_noncvt (valp);

  if (type == BE64 (PROBE_TYPE)
      && val == BE64 (PROBE_VAL64))
    {
      *elfdata = ELFDATA2MSB;
      return true;
    }

  if (type == LE64 (PROBE_TYPE)
      && val == LE64 (PROBE_VAL64))
    {
      *elfdata = ELFDATA2LSB;
      return true;
    }

  return false;
}

static inline bool
do_check32 (const char *a32, uint_fast8_t *elfdata)
{
  /* The AUXV pointer might not even be naturally aligned for 32-bit
     data, because note payloads in a core file are not aligned.  */
  const char *typep = a32 + offsetof (Elf32_auxv_t, a_type);
  uint32_t type = read_4ubyte_unaligned_noncvt (typep);
  const char *valp = a32 + offsetof (Elf32_auxv_t, a_un.a_val);
  uint32_t val = read_4ubyte_unaligned_noncvt (valp);

  if (type == BE32 (PROBE_TYPE)
      && val == BE32 (PROBE_VAL32))
    {
      *elfdata = ELFDATA2MSB;
      return true;
    }

  if (type == LE32 (PROBE_TYPE)
      && val == LE32 (PROBE_VAL32))
    {
      *elfdata = ELFDATA2LSB;
      return true;
    }

  return false;
}

/* Examine an auxv data block and determine its format.
   Return true iff we figured it out.  */
static bool
auxv_format_probe (const void *auxv, size_t size,
		   uint_fast8_t *elfclass, uint_fast8_t *elfdata)
{
  for (size_t i = 0; i < size / sizeof (Elf64_auxv_t); ++i)
    {
      if (do_check64 (auxv + i * sizeof (Elf64_auxv_t), elfdata))
	{
	  *elfclass = ELFCLASS64;
	  return true;
	}

      if (do_check32 (auxv + (i * 2) * sizeof (Elf32_auxv_t), elfdata)
	  || do_check32 (auxv + (i * 2 + 1) * sizeof (Elf32_auxv_t), elfdata))
	{
	  *elfclass = ELFCLASS32;
	  return true;
	}
    }

  return false;
}

/* This is a Dwfl_Memory_Callback that wraps another memory callback.
   If the underlying callback cannot fill the data, then this will
   fall back to fetching data from module files.  */

struct integrated_memory_callback
{
  Dwfl_Memory_Callback *memory_callback;
  void *memory_callback_arg;
  void *buffer;
};

static bool
integrated_memory_callback (Dwfl *dwfl, int ndx,
			       void **buffer, size_t *buffer_available,
			       GElf_Addr vaddr,
			       size_t minread,
			       void *arg)
{
  struct integrated_memory_callback *info = arg;

  if (ndx == -1)
    {
      /* Called for cleanup.  */
      if (info->buffer != NULL)
	{
	  /* The last probe buffer came from the underlying callback.
	     Let it do its cleanup.  */
	  assert (*buffer == info->buffer); /* XXX */
	  *buffer = info->buffer;
	  info->buffer = NULL;
	  return (*info->memory_callback) (dwfl, ndx, buffer, buffer_available,
					   vaddr, minread,
					   info->memory_callback_arg);
	}
      *buffer = NULL;
      *buffer_available = 0;
      return false;
    }

  if (*buffer != NULL)
    /* For a final-read request, we only use the underlying callback.  */
    return (*info->memory_callback) (dwfl, ndx, buffer, buffer_available,
				     vaddr, minread, info->memory_callback_arg);

  /* Let the underlying callback try to fill this request.  */
  if ((*info->memory_callback) (dwfl, ndx, &info->buffer, buffer_available,
				vaddr, minread, info->memory_callback_arg))
    {
      *buffer = info->buffer;
      return true;
    }

  /* Now look for module text covering this address.  */

  Dwfl_Module *mod;
  (void) INTUSE(dwfl_addrsegment) (dwfl, vaddr, &mod);
  if (mod == NULL)
    return false;

  Dwarf_Addr bias;
  Elf_Scn *scn = INTUSE(dwfl_module_address_section) (mod, &vaddr, &bias);
  if (unlikely (scn == NULL))
    {
#if 0 // XXX would have to handle ndx=-1 cleanup calls passed down.
      /* If we have no sections we can try to fill it from the module file
	 based on its phdr mappings.  */
      if (likely (mod->e_type != ET_REL) && mod->main.elf != NULL)
	return INTUSE(dwfl_elf_phdr_memory_callback)
	  (dwfl, 0, buffer, buffer_available,
	   vaddr - mod->main.bias, minread, mod->main.elf);
#endif
      return false;
    }

  Elf_Data *data = elf_rawdata (scn, NULL);
  if (unlikely (data == NULL))
    // XXX throw error?
    return false;

  if (unlikely (data->d_size < vaddr))
    return false;

  /* Provide as much data as we have.  */
  void *contents = data->d_buf + vaddr;
  size_t avail = data->d_size - vaddr;
  if (unlikely (avail < minread))
    return false;

  /* If probing for a string, make sure it's terminated.  */
  if (minread == 0 && unlikely (memchr (contents, '\0', avail) == NULL))
    return false;

  /* We have it! */
  *buffer = contents;
  *buffer_available = avail;
  return true;
}

static size_t
addrsize (uint_fast8_t elfclass)
{
  return elfclass * 4;
}

struct memory_closure
{
  Dwfl *dwfl;
  Dwfl_Memory_Callback *callback;
  void *arg;
};

static inline int
release_buffer (struct memory_closure *closure,
                void **buffer, size_t *buffer_available, int result)
{
  if (*buffer != NULL)
    (*closure->callback) (closure->dwfl, -1, buffer, buffer_available, 0, 0,
                          closure->arg);

  return result;
}

static inline bool
read_addrs (struct memory_closure *closure,
	    uint_fast8_t elfclass, uint_fast8_t elfdata,
	    void **buffer, size_t *buffer_available,
	    GElf_Addr vaddr, GElf_Addr *read_vaddr,
	    size_t n, GElf_Addr *addrs /* [4] */)
{
  size_t nb = n * addrsize (elfclass); /* Address words -> bytes to read.  */
  Dwfl *dwfl = closure->dwfl;

  /* Read a new buffer if the old one doesn't cover these words.  */
  if (*buffer == NULL
      || vaddr < *read_vaddr
      || nb > *buffer_available
      || vaddr - (*read_vaddr) > *buffer_available - nb)
    {
      release_buffer (closure, buffer, buffer_available, 0);

      *read_vaddr = vaddr;
      int segndx = INTUSE(dwfl_addrsegment) (dwfl, vaddr, NULL);
      if (unlikely (segndx < 0)
	  || unlikely (! (*closure->callback) (dwfl, segndx,
					       buffer, buffer_available,
					       vaddr, nb, closure->arg)))
	return true;
    }

  unsigned char *addr = vaddr - (*read_vaddr) + (*buffer);

  if (elfclass == ELFCLASS32)
    {
      if (elfdata == ELFDATA2MSB)
	for (size_t i = 0; i < n; ++i)
	  addrs[i] = BE32 (read_4ubyte_unaligned_noncvt (addr + i * 4));
      else
	for (size_t i = 0; i < n; ++i)
	  addrs[i] = LE32 (read_4ubyte_unaligned_noncvt (addr + i * 4));
    }
  else
    {
      if (elfdata == ELFDATA2MSB)
	for (size_t i = 0; i < n; ++i)
	  addrs[i] = BE64 (read_8ubyte_unaligned_noncvt (addr + i * 8));
      else
	for (size_t i = 0; i < n; ++i)
	  addrs[i] = LE64 (read_8ubyte_unaligned_noncvt (addr + i * 8));
    }

  return false;
}

/* Report a module for each struct link_map in the linked list at r_map
   in the struct r_debug at R_DEBUG_VADDR.  For r_debug_info description
   see dwfl_link_map_report in libdwflP.h.  If R_DEBUG_INFO is not NULL then no
   modules get added to DWFL, caller has to add them from filled in
   R_DEBUG_INFO.

   For each link_map entry, if an existing module resides at its address,
   this just modifies that module's name and suggested file name.  If
   no such module exists, this calls dwfl_report_elf on the l_name string.

   Returns the number of modules found, or -1 for errors.  */

static int
report_r_debug (uint_fast8_t elfclass, uint_fast8_t elfdata,
		Dwfl *dwfl, GElf_Addr r_debug_vaddr,
		Dwfl_Memory_Callback *memory_callback,
		void *memory_callback_arg,
		struct r_debug_info *r_debug_info)
{
  /* Skip r_version, to aligned r_map field.  */
  GElf_Addr read_vaddr = r_debug_vaddr + addrsize (elfclass);

  void *buffer = NULL;
  size_t buffer_available = 0;
  GElf_Addr addrs[4];
  struct memory_closure memory_closure = { dwfl, memory_callback,
                                           memory_callback_arg };
  if (unlikely (read_addrs (&memory_closure, elfclass, elfdata,
			    &buffer, &buffer_available, read_vaddr, &read_vaddr,
			    1, addrs)))
    return release_buffer (&memory_closure, &buffer, &buffer_available, -1);

  GElf_Addr next = addrs[0];

  Dwfl_Module **lastmodp = &dwfl->modulelist;
  int result = 0;

  /* There can't be more elements in the link_map list than there are
     segments.  DWFL->lookup_elts is probably twice that number, so it
     is certainly above the upper bound.  If we iterate too many times,
     there must be a loop in the pointers due to link_map clobberation.  */
  size_t iterations = 0;
  while (next != 0 && ++iterations < dwfl->lookup_elts)
    {
      if (read_addrs (&memory_closure, elfclass, elfdata,
		      &buffer, &buffer_available, next, &read_vaddr,
		      4, addrs))
	return release_buffer (&memory_closure, &buffer, &buffer_available, -1);

      /* Unused: l_addr is the difference between the address in memory
         and the ELF file when the core was created. We need to
         recalculate the difference below because the ELF file we use
         might be differently pre-linked.  */
      // GElf_Addr l_addr = addrs[0];
      GElf_Addr l_name = addrs[1];
      GElf_Addr l_ld = addrs[2];
      next = addrs[3];

      /* If a clobbered or truncated memory image has no useful pointer,
	 just skip this element.  */
      if (l_ld == 0)
	continue;

      /* Fetch the string at the l_name address.  */
      const char *name = NULL;
      if (buffer != NULL
	  && read_vaddr <= l_name
	  && l_name + 1 - read_vaddr < buffer_available
	  && memchr (l_name - read_vaddr + buffer, '\0',
		     buffer_available - (l_name - read_vaddr)) != NULL)
	name = l_name - read_vaddr + buffer;
      else
	{
	  release_buffer (&memory_closure, &buffer, &buffer_available, 0);
	  read_vaddr = l_name;
	  int segndx = INTUSE(dwfl_addrsegment) (dwfl, l_name, NULL);
	  if (likely (segndx >= 0)
	      && (*memory_callback) (dwfl, segndx,
				     &buffer, &buffer_available,
				     l_name, 0, memory_callback_arg))
	    name = buffer;
	}

      if (name != NULL && name[0] == '\0')
	name = NULL;

      if (iterations == 1
	  && dwfl->user_core != NULL
	  && dwfl->user_core->executable_for_core != NULL)
	name = dwfl->user_core->executable_for_core;

      struct r_debug_info_module *r_debug_info_module = NULL;
      if (r_debug_info != NULL)
	{
	  /* Save link map information about valid shared library (or
	     executable) which has not been found on disk.  */
	  const char *name1 = name == NULL ? "" : name;
	  r_debug_info_module = malloc (sizeof (*r_debug_info_module)
					+ strlen (name1) + 1);
	  if (unlikely (r_debug_info_module == NULL))
	    release_buffer (&memory_closure, &buffer,
                            &buffer_available, result);
	  r_debug_info_module->fd = -1;
	  r_debug_info_module->elf = NULL;
	  r_debug_info_module->l_ld = l_ld;
	  r_debug_info_module->start = 0;
	  r_debug_info_module->end = 0;
	  r_debug_info_module->disk_file_has_build_id = false;
	  strcpy (r_debug_info_module->name, name1);
	  r_debug_info_module->next = r_debug_info->module;
	  r_debug_info->module = r_debug_info_module;
	}

      Dwfl_Module *mod = NULL;
      if (name != NULL)
	{
	  /* This code is mostly inlined dwfl_report_elf.  */
	  // XXX hook for sysroot
	  int fd = open (name, O_RDONLY);
	  if (fd >= 0)
	    {
	      Elf *elf;
	      Dwfl_Error error = __libdw_open_file (&fd, &elf, true, false);
	      GElf_Addr elf_dynamic_vaddr;
	      if (error == DWFL_E_NOERROR
		  && __libdwfl_dynamic_vaddr_get (elf, &elf_dynamic_vaddr))
		{
		  const void *build_id_bits;
		  GElf_Addr build_id_elfaddr;
		  int build_id_len;
		  bool valid = true;

		  if (__libdwfl_find_elf_build_id (NULL, elf, &build_id_bits,
						   &build_id_elfaddr,
						   &build_id_len) > 0
		      && build_id_elfaddr != 0)
		    {
		      if (r_debug_info_module != NULL)
			r_debug_info_module->disk_file_has_build_id = true;
		      GElf_Addr build_id_vaddr = (build_id_elfaddr
						  - elf_dynamic_vaddr + l_ld);

		      release_buffer (&memory_closure, &buffer,
				      &buffer_available, 0);
		      int segndx = INTUSE(dwfl_addrsegment) (dwfl,
							     build_id_vaddr,
							     NULL);
		      if (! (*memory_callback) (dwfl, segndx,
						&buffer, &buffer_available,
						build_id_vaddr, build_id_len,
						memory_callback_arg))
			{
			  /* File has valid build-id which cannot be read from
			     memory.  This happens for core files without bit 4
			     (0x10) set in Linux /proc/PID/coredump_filter.  */
			}
		      else
			{
			  if (memcmp (build_id_bits, buffer, build_id_len) != 0)
			    /* File has valid build-id which does not match
			       the one in memory.  */
			    valid = false;
			  release_buffer (&memory_closure, &buffer,
					  &buffer_available, 0);

			}
		    }

		  if (valid)
		    {
		      // It is like l_addr but it handles differently prelinked
		      // files at core dumping vs. core loading time.
		      GElf_Addr base = l_ld - elf_dynamic_vaddr;
		      if (r_debug_info_module == NULL)
			{
			  // XXX hook for sysroot
			  mod = __libdwfl_report_elf (dwfl, basename (name),
						      name, fd, elf, base,
						      true, true);
			  if (mod != NULL)
			    {
			      elf = NULL;
			      fd = -1;
			    }
			}
		      else if (__libdwfl_elf_address_range (elf, base, true,
							    true, NULL, NULL,
						    &r_debug_info_module->start,
						    &r_debug_info_module->end,
							    NULL, NULL))
			{
			  r_debug_info_module->elf = elf;
			  r_debug_info_module->fd = fd;
			  elf = NULL;
			  fd = -1;
			}
		    }
		  if (elf != NULL)
		    elf_end (elf);
		  if (fd != -1)
		    close (fd);
		}
	    }
	}

      if (mod != NULL)
	{
	  ++result;

	  /* Move this module to the end of the list, so that we end
	     up with a list in the same order as the link_map chain.  */
	  if (mod->next != NULL)
	    {
	      if (*lastmodp != mod)
		{
		  lastmodp = &dwfl->modulelist;
		  while (*lastmodp != mod)
		    lastmodp = &(*lastmodp)->next;
		}
	      *lastmodp = mod->next;
	      mod->next = NULL;
	      while (*lastmodp != NULL)
		lastmodp = &(*lastmodp)->next;
	      *lastmodp = mod;
	    }

	  lastmodp = &mod->next;
	}
    }

  return release_buffer (&memory_closure, &buffer, &buffer_available, result);
}

static GElf_Addr
consider_executable (Dwfl_Module *mod, GElf_Addr at_phdr, GElf_Addr at_entry,
		     uint_fast8_t *elfclass, uint_fast8_t *elfdata,
		     Dwfl_Memory_Callback *memory_callback,
		     void *memory_callback_arg)
{
  GElf_Ehdr ehdr;
  if (unlikely (gelf_getehdr (mod->main.elf, &ehdr) == NULL))
    return 0;

  if (at_entry != 0)
    {
      /* If we have an AT_ENTRY value, reject this executable if
	 its entry point address could not have supplied that.  */

      if (ehdr.e_entry == 0)
	return 0;

      if (mod->e_type == ET_EXEC)
	{
	  if (ehdr.e_entry != at_entry)
	    return 0;
	}
      else
	{
	  /* It could be a PIE.  */
	}
    }

  // XXX this could be saved in the file cache: phdr vaddr, DT_DEBUG d_val vaddr
  /* Find the vaddr of the DT_DEBUG's d_ptr.  This is the memory
     address where &r_debug was written at runtime.  */
  GElf_Xword align = mod->dwfl->segment_align;
  GElf_Addr d_val_vaddr = 0;
  size_t phnum;
  if (elf_getphdrnum (mod->main.elf, &phnum) != 0)
    return 0;

  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_align > 1 && (align == 0 || phdr->p_align < align))
	align = phdr->p_align;

      if (at_phdr != 0
	  && phdr->p_type == PT_LOAD
	  && (phdr->p_offset & -align) == (ehdr.e_phoff & -align))
	{
	  /* This is the segment that would map the phdrs.
	     If we have an AT_PHDR value, reject this executable
	     if its phdr mapping could not have supplied that.  */
	  if (mod->e_type == ET_EXEC)
	    {
	      if (ehdr.e_phoff - phdr->p_offset + phdr->p_vaddr != at_phdr)
		return 0;
	    }
	  else
	    {
	      /* It could be a PIE.  If the AT_PHDR value and our
		 phdr address don't match modulo ALIGN, then this
		 could not have been the right PIE.  */
	      if (((ehdr.e_phoff - phdr->p_offset + phdr->p_vaddr) & -align)
		  != (at_phdr & -align))
		return 0;

	      /* Calculate the bias applied to the PIE's p_vaddr values.  */
	      GElf_Addr bias = (at_phdr - (ehdr.e_phoff - phdr->p_offset
					   + phdr->p_vaddr));

	      /* Final sanity check: if we have an AT_ENTRY value,
		 reject this PIE unless its biased e_entry matches.  */
	      if (at_entry != 0 && at_entry != ehdr.e_entry + bias)
		return 0;

	      /* If we're changing the module's address range,
		 we've just invalidated the module lookup table.  */
	      GElf_Addr mod_bias = dwfl_adjusted_address (mod, 0);
	      if (bias != mod_bias)
		{
		  mod->low_addr -= mod_bias;
		  mod->high_addr -= mod_bias;
		  mod->low_addr += bias;
		  mod->high_addr += bias;

		  free (mod->dwfl->lookup_module);
		  mod->dwfl->lookup_module = NULL;
		}
	    }
	}

      if (phdr->p_type == PT_DYNAMIC)
	{
	  Elf_Data *data = elf_getdata_rawchunk (mod->main.elf, phdr->p_offset,
						 phdr->p_filesz, ELF_T_DYN);
	  if (data == NULL)
	    continue;
	  const size_t entsize = gelf_fsize (mod->main.elf,
					     ELF_T_DYN, 1, EV_CURRENT);
	  const size_t n = data->d_size / entsize;
	  for (size_t j = 0; j < n; ++j)
	    {
	      GElf_Dyn dyn_mem;
	      GElf_Dyn *dyn = gelf_getdyn (data, j, &dyn_mem);
	      if (dyn != NULL && dyn->d_tag == DT_DEBUG)
		{
		  d_val_vaddr = phdr->p_vaddr + entsize * j + entsize / 2;
		  break;
		}
	    }
	}
    }

  if (d_val_vaddr != 0)
    {
      /* Now we have the final address from which to read &r_debug.  */
      d_val_vaddr = dwfl_adjusted_address (mod, d_val_vaddr);

      void *buffer = NULL;
      size_t buffer_available = addrsize (ehdr.e_ident[EI_CLASS]);

      int segndx = INTUSE(dwfl_addrsegment) (mod->dwfl, d_val_vaddr, NULL);

      if ((*memory_callback) (mod->dwfl, segndx,
			      &buffer, &buffer_available,
			      d_val_vaddr, buffer_available,
			      memory_callback_arg))
	{
	  const union
	  {
	    Elf32_Addr a32;
	    Elf64_Addr a64;
	  } *u = buffer;

	  GElf_Addr vaddr;
	  if (ehdr.e_ident[EI_CLASS] == ELFCLASS32)
	    vaddr = (ehdr.e_ident[EI_DATA] == ELFDATA2MSB
		     ? BE32 (u->a32) : LE32 (u->a32));
	  else
	    vaddr = (ehdr.e_ident[EI_DATA] == ELFDATA2MSB
		     ? BE64 (u->a64) : LE64 (u->a64));

	  (*memory_callback) (mod->dwfl, -1, &buffer, &buffer_available, 0, 0,
			      memory_callback_arg);

	  if (*elfclass == ELFCLASSNONE)
	    *elfclass = ehdr.e_ident[EI_CLASS];
	  else if (*elfclass != ehdr.e_ident[EI_CLASS])
	    return 0;

	  if (*elfdata == ELFDATANONE)
	    *elfdata = ehdr.e_ident[EI_DATA];
	  else if (*elfdata != ehdr.e_ident[EI_DATA])
	    return 0;

	  return vaddr;
	}
    }

  return 0;
}

/* Try to find an existing executable module with a DT_DEBUG.  */
static GElf_Addr
find_executable (Dwfl *dwfl, GElf_Addr at_phdr, GElf_Addr at_entry,
		 uint_fast8_t *elfclass, uint_fast8_t *elfdata,
		 Dwfl_Memory_Callback *memory_callback,
		 void *memory_callback_arg)
{
  for (Dwfl_Module *mod = dwfl->modulelist; mod != NULL; mod = mod->next)
    if (mod->main.elf != NULL)
      {
	GElf_Addr r_debug_vaddr = consider_executable (mod, at_phdr, at_entry,
						       elfclass, elfdata,
						       memory_callback,
						       memory_callback_arg);
	if (r_debug_vaddr != 0)
	  return r_debug_vaddr;
      }

  return 0;
}


int
dwfl_link_map_report (Dwfl *dwfl, const void *auxv, size_t auxv_size,
		      Dwfl_Memory_Callback *memory_callback,
		      void *memory_callback_arg,
		      struct r_debug_info *r_debug_info)
{
  GElf_Addr r_debug_vaddr = 0;

  uint_fast8_t elfclass = ELFCLASSNONE;
  uint_fast8_t elfdata = ELFDATANONE;
  if (likely (auxv != NULL)
      && likely (auxv_format_probe (auxv, auxv_size, &elfclass, &elfdata)))
    {
      GElf_Addr entry = 0;
      GElf_Addr phdr = 0;
      GElf_Xword phent = 0;
      GElf_Xword phnum = 0;

#define READ_AUXV32(ptr)	read_4ubyte_unaligned_noncvt (ptr)
#define READ_AUXV64(ptr)	read_8ubyte_unaligned_noncvt (ptr)
#define AUXV_SCAN(NN, BL) do                                            \
	{                                                               \
	  const Elf##NN##_auxv_t *av = auxv;                            \
	  for (size_t i = 0; i < auxv_size / sizeof av[0]; ++i)         \
	    {                                                           \
	      const char *typep = auxv + i * sizeof (Elf##NN##_auxv_t); \
	      typep += offsetof (Elf##NN##_auxv_t, a_type);             \
	      uint##NN##_t type = READ_AUXV##NN (typep);                \
	      const char *valp = auxv + i * sizeof (Elf##NN##_auxv_t);  \
	      valp += offsetof (Elf##NN##_auxv_t, a_un.a_val);          \
	      uint##NN##_t val = BL##NN (READ_AUXV##NN (valp));         \
	      if (type == BL##NN (AT_ENTRY))                            \
		entry = val;                                            \
	      else if (type == BL##NN (AT_PHDR))                        \
		phdr = val;                                             \
	      else if (type == BL##NN (AT_PHNUM))                       \
		phnum = val;                                            \
	      else if (type == BL##NN (AT_PHENT))                       \
		phent = val;                                            \
	      else if (type == BL##NN (AT_PAGESZ))                      \
		{                                                       \
		  if (val > 1                                           \
		      && (dwfl->segment_align == 0                      \
			  || val < dwfl->segment_align))                \
		    dwfl->segment_align = val;                          \
		}                                                       \
	    }                                                           \
	}                                                               \
      while (0)

      if (elfclass == ELFCLASS32)
	{
	  if (elfdata == ELFDATA2MSB)
	    AUXV_SCAN (32, BE);
	  else
	    AUXV_SCAN (32, LE);
	}
      else
	{
	  if (elfdata == ELFDATA2MSB)
	    AUXV_SCAN (64, BE);
	  else
	    AUXV_SCAN (64, LE);
	}

      /* If we found the phdr dimensions, search phdrs for PT_DYNAMIC.  */
      GElf_Addr dyn_vaddr = 0;
      GElf_Xword dyn_filesz = 0;
      GElf_Addr dyn_bias = (GElf_Addr) -1;

      if (phdr != 0 && phnum != 0
	  && ((elfclass == ELFCLASS32 && phent == sizeof (Elf32_Phdr))
	      || (elfclass == ELFCLASS64 && phent == sizeof (Elf64_Phdr))))
	{
	  Dwfl_Module *phdr_mod;
	  int phdr_segndx = INTUSE(dwfl_addrsegment) (dwfl, phdr, &phdr_mod);
	  Elf_Data in =
	    {
	      .d_type = ELF_T_PHDR,
	      .d_version = EV_CURRENT,
	      .d_size = phnum * phent,
	      .d_buf = NULL
	    };
	  bool in_ok = (*memory_callback) (dwfl, phdr_segndx, &in.d_buf,
					   &in.d_size, phdr, phnum * phent,
					   memory_callback_arg);
	  bool in_from_exec = false;
	  if (! in_ok
	      && dwfl->user_core != NULL
	      && dwfl->user_core->executable_for_core != NULL)
	    {
	      /* AUXV -> PHDR -> DYNAMIC
		 Both AUXV and DYNAMIC should be always present in a core file.
		 PHDR may be missing in core file, try to read it from
		 EXECUTABLE_FOR_CORE to find where DYNAMIC is located in the
		 core file.  */

	      int fd = open (dwfl->user_core->executable_for_core, O_RDONLY);
	      Elf *elf;
	      Dwfl_Error error = DWFL_E_ERRNO;
	      if (fd != -1)
		error = __libdw_open_file (&fd, &elf, true, false);
	      if (error != DWFL_E_NOERROR)
		{
		  __libdwfl_seterrno (error);
		  return false;
		}
	      GElf_Ehdr ehdr_mem, *ehdr = gelf_getehdr (elf, &ehdr_mem);
	      if (ehdr == NULL)
		{
		  elf_end (elf);
		  close (fd);
		  __libdwfl_seterrno (DWFL_E_LIBELF);
		  return false;
		}
	      size_t e_phnum;
	      if (elf_getphdrnum (elf, &e_phnum) != 0)
		{
		  elf_end (elf);
		  close (fd);
		  __libdwfl_seterrno (DWFL_E_LIBELF);
		  return false;
		}
	      if (e_phnum != phnum || ehdr->e_phentsize != phent)
		{
		  elf_end (elf);
		  close (fd);
		  __libdwfl_seterrno (DWFL_E_BADELF);
		  return false;
		}
	      off_t off = ehdr->e_phoff;
	      assert (in.d_buf == NULL);
	      /* Note this in the !in_ok path.  That means memory_callback
		 failed.  But the callback might still have reset the d_size
		 value (to zero).  So explicitly set it here again.  */
	      if (unlikely (phnum > SIZE_MAX / phent))
		{
		  __libdwfl_seterrno (DWFL_E_NOMEM);
		  return false;
		}
	      in.d_size = phnum * phent;
	      in.d_buf = malloc (in.d_size);
	      if (unlikely (in.d_buf == NULL))
		{
		  elf_end (elf);
		  close (fd);
		  __libdwfl_seterrno (DWFL_E_NOMEM);
		  return false;
		}
	      ssize_t nread = pread_retry (fd, in.d_buf, in.d_size, off);
	      elf_end (elf);
	      close (fd);
	      if (nread != (ssize_t) in.d_size)
		{
		  free (in.d_buf);
		  __libdwfl_seterrno (DWFL_E_ERRNO);
		  return false;
		}
	      in_ok = true;
	      in_from_exec = true;
	    }
	  if (in_ok)
	    {
	      if (unlikely (phnum > SIZE_MAX / phent))
		{
		  __libdwfl_seterrno (DWFL_E_NOMEM);
		  return false;
		}
	      size_t nbytes = phnum * phent;
	      /* We can only process as many bytes/phnum as there are
		 in in.d_size. The data might have been truncated.  */
	      if (nbytes > in.d_size)
		{
		  nbytes = in.d_size;
		  phnum = nbytes / phent;
		  if (phnum == 0)
		    {
		      __libdwfl_seterrno (DWFL_E_BADELF);
		      return false;
		    }
		}
	      void *buf = malloc (nbytes);
	      Elf32_Phdr (*p32)[phnum] = buf;
	      Elf64_Phdr (*p64)[phnum] = buf;
	      if (unlikely (buf == NULL))
		{
		  __libdwfl_seterrno (DWFL_E_NOMEM);
		  return false;
		}
	      Elf_Data out =
		{
		  .d_type = ELF_T_PHDR,
		  .d_version = EV_CURRENT,
		  .d_size = nbytes,
		  .d_buf = buf
		};
	      if (in.d_size > out.d_size)
		{
		  in.d_size = out.d_size;
		  phnum = in.d_size / phent;
		  if (phnum == 0)
		    {
		      free (buf);
		      __libdwfl_seterrno (DWFL_E_BADELF);
		      return false;
		    }
		}
	      bool is32 = (elfclass == ELFCLASS32);
	      size_t phdr_align = (is32
				   ? __alignof__ (Elf32_Phdr)
				   : __alignof__ (Elf64_Phdr));
	      if (!in_from_exec
		  && ((uintptr_t) in.d_buf & (phdr_align - 1)) != 0)
		{
		  memcpy (out.d_buf, in.d_buf, in.d_size);
		  in.d_buf = out.d_buf;
		}
	      if (likely ((elfclass == ELFCLASS32
			   ? elf32_xlatetom : elf64_xlatetom)
			  (&out, &in, elfdata) != NULL))
		{
		  for (size_t i = 0; i < phnum; ++i)
		    {
		      GElf_Word type = (is32
					? (*p32)[i].p_type
					: (*p64)[i].p_type);
		      GElf_Addr vaddr = (is32
					 ? (*p32)[i].p_vaddr
					 : (*p64)[i].p_vaddr);
		      GElf_Xword filesz = (is32
					   ? (*p32)[i].p_filesz
					   : (*p64)[i].p_filesz);

		      if (type == PT_PHDR)
			{
			  if (dyn_bias == (GElf_Addr) -1
			      /* Do a sanity check on the putative address.  */
			      && ((vaddr & (dwfl->segment_align - 1))
				  == (phdr & (dwfl->segment_align - 1))))
			    {
			      dyn_bias = phdr - vaddr;
			      if (dyn_vaddr != 0)
				break;
			    }

			}
		      else if (type == PT_DYNAMIC)
			{
			  dyn_vaddr = vaddr;
			  dyn_filesz = filesz;
			  if (dyn_bias != (GElf_Addr) -1)
			    break;
			}
		    }
		}

	      if (in_from_exec)
		free (in.d_buf);
	      else
		(*memory_callback) (dwfl, -1, &in.d_buf, &in.d_size, 0, 0,
				    memory_callback_arg);
	      free (buf);
	    }
	  else
	    /* We could not read the executable's phdrs from the
	       memory image.  If we have a presupplied executable,
	       we can still use the AT_PHDR and AT_ENTRY values to
	       verify it, and to adjust its bias if it's a PIE.

	       If there was an ET_EXEC module presupplied that contains
	       the AT_PHDR address, then we only consider that one.
	       We'll either accept it if its phdr location and e_entry
	       make sense or reject it if they don't.  If there is no
	       presupplied ET_EXEC, then look for a presupplied module,
	       which might be a PIE (ET_DYN) that needs its bias adjusted.  */
	    r_debug_vaddr = ((phdr_mod == NULL
			      || phdr_mod->main.elf == NULL
			      || phdr_mod->e_type != ET_EXEC)
			     ? find_executable (dwfl, phdr, entry,
						&elfclass, &elfdata,
						memory_callback,
						memory_callback_arg)
			     : consider_executable (phdr_mod, phdr, entry,
						    &elfclass, &elfdata,
						    memory_callback,
						    memory_callback_arg));
	}

      /* If we found PT_DYNAMIC, search it for DT_DEBUG.  */
      if (dyn_filesz != 0)
	{
	  if (dyn_bias != (GElf_Addr) -1)
	    dyn_vaddr += dyn_bias;

	  Elf_Data in =
	    {
	      .d_type = ELF_T_DYN,
	      .d_version = EV_CURRENT,
	      .d_size = dyn_filesz,
	      .d_buf = NULL
	    };
	  int dyn_segndx = dwfl_addrsegment (dwfl, dyn_vaddr, NULL);
	  if ((*memory_callback) (dwfl, dyn_segndx, &in.d_buf, &in.d_size,
				  dyn_vaddr, dyn_filesz, memory_callback_arg))
	    {
	      size_t entsize = (elfclass == ELFCLASS32
				? sizeof (Elf32_Dyn) : sizeof (Elf64_Dyn));
	      if (unlikely (dyn_filesz > SIZE_MAX / entsize))
		{
		  __libdwfl_seterrno (DWFL_E_NOMEM);
		  return false;
		}
	      /* We can only process as many bytes as there are in
	         in.d_size. The data might have been truncated.  */
	      if (dyn_filesz > in.d_size)
		dyn_filesz = in.d_size;
	      if (dyn_filesz / entsize == 0)
		{
		  __libdwfl_seterrno (DWFL_E_BADELF);
		  return false;
		}
	      void *buf = malloc (dyn_filesz);
	      if (unlikely (buf == NULL))
		{
		  __libdwfl_seterrno (DWFL_E_NOMEM);
		  return false;
		}
	      Elf_Data out =
		{
		  .d_type = ELF_T_DYN,
		  .d_version = EV_CURRENT,
		  .d_size = dyn_filesz,
		  .d_buf = buf
		};
	      if (in.d_size > out.d_size)
		in.d_size = out.d_size;
	      size_t dyn_align = (elfclass == ELFCLASS32
			          ? __alignof__ (Elf32_Dyn)
				  : __alignof__ (Elf64_Dyn));
	      if (((uintptr_t) in.d_buf & (dyn_align - 1)) != 0)
		{
		  memcpy (out.d_buf, in.d_buf, in.d_size);
		  in.d_buf = out.d_buf;
		}
	      if (likely ((elfclass == ELFCLASS32
			   ? elf32_xlatetom : elf64_xlatetom)
			  (&out, &in, elfdata) != NULL))
		{
		  /* We are looking for DT_DEBUG.  */
		  if (elfclass == ELFCLASS32)
		    {
		      Elf32_Dyn (*d32)[dyn_filesz / sizeof (Elf32_Dyn)] = buf;
		      size_t n = dyn_filesz / sizeof (Elf32_Dyn);
		      for (size_t i = 0; i < n; ++i)
			if ((*d32)[i].d_tag == DT_DEBUG)
			  {
			    r_debug_vaddr = (*d32)[i].d_un.d_val;
			    break;
			  }
		    }
		  else
		    {
		      Elf64_Dyn (*d64)[dyn_filesz / sizeof (Elf64_Dyn)] = buf;
		      size_t n = dyn_filesz / sizeof (Elf64_Dyn);
		      for (size_t i = 0; i < n; ++i)
			if ((*d64)[i].d_tag == DT_DEBUG)
			  {
			    r_debug_vaddr = (*d64)[i].d_un.d_val;
			    break;
			  }
		    }
		}

	      (*memory_callback) (dwfl, -1, &in.d_buf, &in.d_size, 0, 0,
				  memory_callback_arg);
	      free (buf);
	    }
	}
    }
  else
    /* We have to look for a presupplied executable file to determine
       the vaddr of its dynamic section and DT_DEBUG therein.  */
    r_debug_vaddr = find_executable (dwfl, 0, 0, &elfclass, &elfdata,
				     memory_callback, memory_callback_arg);

  if (r_debug_vaddr == 0)
    return 0;

  /* For following pointers from struct link_map, we will use an
     integrated memory access callback that can consult module text
     elided from the core file.  This is necessary when the l_name
     pointer for the dynamic linker's own entry is a pointer into the
     executable's .interp section.  */
  struct integrated_memory_callback mcb =
    {
      .memory_callback = memory_callback,
      .memory_callback_arg = memory_callback_arg
    };

  /* Now we can follow the dynamic linker's library list.  */
  return report_r_debug (elfclass, elfdata, dwfl, r_debug_vaddr,
			 &integrated_memory_callback, &mcb, r_debug_info);
}
INTDEF (dwfl_link_map_report)