libdwfl/core-file.c

/* Core file handling.
   Copyright (C) 2008 Red Hat, Inc.
   This file is part of Red Hat elfutils.

   Red Hat elfutils 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; version 2 of the License.

   Red Hat 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 a copy of the GNU General Public License along
   with Red Hat elfutils; if not, write to the Free Software Foundation,
   Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301 USA.

   In addition, as a special exception, Red Hat, Inc. gives You the
   additional right to link the code of Red Hat elfutils with code licensed
   under any Open Source Initiative certified open source license
   (http://www.opensource.org/licenses/index.php) which requires the
   distribution of source code with any binary distribution and to
   distribute linked combinations of the two.  Non-GPL Code permitted under
   this exception must only link to the code of Red Hat elfutils through
   those well defined interfaces identified in the file named EXCEPTION
   found in the source code files (the "Approved Interfaces").  The files
   of Non-GPL Code may instantiate templates or use macros or inline
   functions from the Approved Interfaces without causing the resulting
   work to be covered by the GNU General Public License.  Only Red Hat,
   Inc. may make changes or additions to the list of Approved Interfaces.
   Red Hat's grant of this exception is conditioned upon your not adding
   any new exceptions.  If you wish to add a new Approved Interface or
   exception, please contact Red Hat.  You must obey the GNU General Public
   License in all respects for all of the Red Hat elfutils code and other
   code used in conjunction with Red Hat elfutils except the Non-GPL Code
   covered by this exception.  If you modify this file, you may extend this
   exception to your version of the file, but you are not obligated to do
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   you must delete this exception statement from your version and license
   this file solely under the GPL without exception.

   Red Hat elfutils is an included package of the Open Invention Network.
   An included package of the Open Invention Network is a package for which
   Open Invention Network licensees cross-license their patents.  No patent
   license is granted, either expressly or impliedly, by designation as an
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   <http://www.openinventionnetwork.com>.  */

#include <config.h>
#include "../libelf/libelfP.h"	/* For NOTE_ALIGN.  */
#undef	_
#include "libdwflP.h"
#include <gelf.h>

#include <sys/param.h>
#include <unistd.h>
#include <endian.h>
#include <byteswap.h>
#include "system.h"


/* This is a prototype of what a new libelf interface might be.
   This implementation is pessimal for non-mmap cases and should
   be replaced by more diddling inside libelf internals.  */
static Elf *
elf_begin_rand (Elf *parent, loff_t offset, loff_t size, loff_t *next)
{
  if (parent == NULL)
    return NULL;

  /* On failure return, we update *NEXT to point back at OFFSET.  */
  inline Elf *fail (int error)
  {
    if (next != NULL)
      *next = offset;
    //__libelf_seterrno (error);
    __libdwfl_seterrno (DWFL_E (LIBELF, error));
    return NULL;
  }

  loff_t min = (parent->kind == ELF_K_ELF ?
		(parent->class == ELFCLASS32
		 ? sizeof (Elf32_Ehdr) : sizeof (Elf64_Ehdr))
		: parent->kind == ELF_K_AR ? SARMAG
		: 0);

  if (unlikely (offset < min)
      || unlikely (offset >= (loff_t) parent->maximum_size))
    return fail (ELF_E_RANGE);

  /* For an archive, fetch just the size field
     from the archive header to override SIZE.  */
  if (parent->kind == ELF_K_AR)
    {
      struct ar_hdr h = { .ar_size = "" };

      if (unlikely (parent->maximum_size - offset < sizeof h))
	return fail (ELF_E_RANGE);

      if (parent->map_address != NULL)
	memcpy (h.ar_size, parent->map_address + parent->start_offset + offset,
		sizeof h.ar_size);
      else if (unlikely (pread_retry (parent->fildes,
				      h.ar_size, sizeof (h.ar_size),
				      parent->start_offset + offset
				      + offsetof (struct ar_hdr, ar_size))
			 != sizeof (h.ar_size)))
	return fail (ELF_E_READ_ERROR);

      offset += sizeof h;

      char *endp;
      size = strtoll (h.ar_size, &endp, 10);
      if (unlikely (endp == h.ar_size)
	  || unlikely ((loff_t) parent->maximum_size - offset < size))
	return fail (ELF_E_INVALID_ARCHIVE);
    }

  if (unlikely ((loff_t) parent->maximum_size - offset < size))
    return fail (ELF_E_RANGE);

  /* Even if we fail at this point, update *NEXT to point past the file.  */
  if (next != NULL)
    *next = offset + size;

  if (unlikely (offset == 0)
      && unlikely (size == (loff_t) parent->maximum_size))
    return elf_clone (parent, parent->cmd);

  /* Note the image is guaranteed live only as long as PARENT
     lives.  Using elf_memory is quite suboptimal if the whole
     file is not mmap'd.  We really should have something like
     a generalization of the archive support.  */
  Elf_Data *data = elf_getdata_rawchunk (parent, offset, size, ELF_T_BYTE);
  if (data == NULL)
    return NULL;
  assert ((loff_t) data->d_size == size);
  return elf_memory (data->d_buf, size);
}


int
dwfl_report_core_segments (Dwfl *dwfl, Elf *elf, const GElf_Ehdr *ehdr,
			   GElf_Phdr *notes)
{
  if (unlikely (dwfl == NULL))
    return -1;

  if (unlikely (elf == NULL) || unlikely (ehdr == NULL))
    {
      __libdw_seterrno (DWFL_E_LIBELF);
      return -1;
    }

  int result = 0;

  if (notes != NULL)
    notes->p_type = PT_NULL;

  for (int ndx = 0; result >= 0 && ndx < ehdr->e_phnum; ++ndx)
    {
      GElf_Phdr phdr_mem;
      GElf_Phdr *phdr = gelf_getphdr (elf, ndx, &phdr_mem);
      if (unlikely (phdr == NULL))
	{
	  __libdwfl_seterrno (DWFL_E_LIBELF);
	  return -1;
	}
      switch (phdr->p_type)
	{
	case PT_LOAD:
	  result = dwfl_report_segment (dwfl, ndx, phdr, 0, NULL);
	  break;

	case PT_NOTE:
	  if (notes != NULL)
	    {
	      *notes = *phdr;
	      notes = NULL;
	    }
	  break;
	}
    }

  return result;
}

/* Never read more than this much without mmap.  */
#define MAX_EAGER_COST	8192

static bool
core_file_read_eagerly (Dwfl_Module *mod,
			void **userdata __attribute__ ((unused)),
			const char *name __attribute__ ((unused)),
			Dwarf_Addr start __attribute__ ((unused)),
			void **buffer, size_t *buffer_available,
			GElf_Off cost, GElf_Off worthwhile,
			GElf_Off whole,
			GElf_Off contiguous __attribute__ ((unused)),
			void *arg, Elf **elfp)
{
  Elf *core = arg;

  if (whole <= *buffer_available)
    {
      /* All there ever was, we already have on hand.  */

      if (core->map_address == NULL)
	{
	  /* We already malloc'd the buffer.  */
	  *elfp = elf_memory (*buffer, whole);
	  if (unlikely (*elfp == NULL))
	    return false;

	  (*elfp)->flags |= ELF_F_MALLOCED;
	  *buffer = NULL;
	  *buffer_available = 0;
	  return true;
	}

      /* We can use the image inside the core file directly.  */
      *elfp = elf_begin_rand (core, *buffer - core->map_address, whole, NULL);
      *buffer = NULL;
      *buffer_available = 0;
      return *elfp != NULL;
    }

  /* We don't have the whole file.
     Figure out if this is better than nothing.  */

  if (worthwhile == 0)
    /* Caller doesn't think so.  */
    return false;

  /*
    XXX would like to fall back to partial file via memory
    when build id find_elf fails
    also, link_map name may give file name from disk better than partial here
    requires find_elf hook re-doing the magic to fall back if no file found
  */

  if (mod->build_id_len > 0)
    /* There is a build ID that could help us find the whole file,
       which might be more useful than what we have.
       We'll just rely on that.  */
    return false;

  if (core->map_address != NULL)
    /* It's cheap to get, so get it.  */
    return true;

  /* Only use it if there isn't too much to be read.  */
  return cost <= MAX_EAGER_COST;
}

bool
dwfl_elf_phdr_memory_callback (Dwfl *dwfl, int ndx,
			       void **buffer, size_t *buffer_available,
			       GElf_Addr vaddr,
			       size_t minread,
			       void *arg)
{
  Elf *elf = arg;

  if (ndx == -1)
    {
      /* Called for cleanup.  */
      if (elf->map_address == NULL)
	free (*buffer);
      *buffer = NULL;
      *buffer_available = 0;
      return false;
    }

  const GElf_Off align = dwfl->segment_align ?: 1;
  GElf_Phdr phdr;

  do
    if (unlikely (gelf_getphdr (elf, ndx++, &phdr) == NULL))
      return true;
  while (phdr.p_type != PT_LOAD
	 || ((phdr.p_vaddr + phdr.p_memsz + align - 1) & -align) <= vaddr);

  GElf_Off start = vaddr - phdr.p_vaddr + phdr.p_offset;
  GElf_Off end = (phdr.p_offset + phdr.p_filesz + align - 1) & -align;

  /* Use following contiguous segments to get towards SIZE.  */
  inline bool more (size_t size)
  {
    while (end <= start || end - start < size)
      {
	if (phdr.p_filesz < phdr.p_memsz)
	  /* This segment is truncated, so no following one helps us.  */
	  return false;

	if (unlikely (gelf_getphdr (elf, ndx++, &phdr) == NULL))
	  return false;

	if (phdr.p_type == PT_LOAD)
	  {
	    if (phdr.p_offset > end)
	      /* It's discontiguous!  */
	      return false;

	    end = (phdr.p_offset + phdr.p_filesz + align - 1) & -align;
	  }
      }
    return true;
  }

  /* We need at least this much.  */
  if (! more (minread))
    return false;

  /* See how much more we can get of what the caller wants.  */
  (void) more (*buffer_available);

  /* If it's already on hand anyway, use as much as there is.  */
  if (elf->map_address != NULL)
    (void) more (elf->maximum_size - start);

  if (unlikely (end - start > elf->maximum_size))
    end = start + elf->maximum_size;

  if (elf->map_address != NULL)
    {
      void *contents = elf->map_address + elf->start_offset + start;
      size_t size = end - start;

      if (minread == 0)		/* String mode.  */
	{
	  const void *eos = memchr (contents, '\0', size);
	  if (unlikely (eos == NULL) || unlikely (eos == contents))
	    return false;
	  size = eos + 1 - contents;
	}

      if (*buffer == NULL)
	{
	  *buffer = contents;
	  *buffer_available = size;
	}
      else
	{
	  *buffer_available = MIN (size, *buffer_available);
	  memcpy (*buffer, contents, *buffer_available);
	}
    }
  else
    {
      void *into = *buffer;
      if (*buffer == NULL)
	{
	  *buffer_available = MIN (minread ?: 512,
				   MAX (4096, MIN (end - start,
						   *buffer_available)));
	  into = malloc (*buffer_available);
	  if (unlikely (into == NULL))
	    {
	      __libdwfl_seterrno (DWFL_E_NOMEM);
	      return false;
	    }
	}

      ssize_t nread = pread_retry (elf->fildes, into, *buffer_available, start);
      if (nread < (ssize_t) minread)
	{
	  if (into != *buffer)
	    free (into);
	  if (nread < 0)
	    __libdwfl_seterrno (DWFL_E_ERRNO);
	  return false;
	}

      if (minread == 0)		/* String mode.  */
	{
	  const void *eos = memchr (into, '\0', nread);
	  if (unlikely (eos == NULL) || unlikely (eos == into))
	    {
	      if (*buffer == NULL)
		free (into);
	      return false;
	    }
	  nread = eos + 1 - into;
	}

      if (*buffer == NULL)
	*buffer = into;
      *buffer_available = nread;
    }

  return true;
}

int
dwfl_core_file_report (Dwfl *dwfl, Elf *elf, const GElf_Ehdr *ehdr)
{
  GElf_Phdr notes_phdr;

  /* First report each PT_LOAD segment.  */
  int ndx = dwfl_report_core_segments (dwfl, elf, ehdr, &notes_phdr);
  if (unlikely (ndx <= 0))
    return ndx;

  /* Now sniff segment contents for modules.  */
  ndx = 0;
  do
    {
      int seg = dwfl_segment_report_module (dwfl, ndx, NULL,
					    &dwfl_elf_phdr_memory_callback, elf,
					    core_file_read_eagerly, elf);
      if (unlikely (seg < 0))
	return seg;
      ndx = seg > ndx ? seg : ndx + 1;
    }
  while (ndx < ehdr->e_phnum);

  /* Next, we should follow the chain from DT_DEBUG.  */

  const void *auxv = NULL;
  size_t auxv_size = 0;
  if (likely (notes_phdr.p_type == PT_NOTE))
    {
      /* PT_NOTE -> NT_AUXV -> AT_PHDR -> PT_DYNAMIC -> DT_DEBUG */

      Elf_Data *notes = elf_getdata_rawchunk (elf,
					      notes_phdr.p_offset,
					      notes_phdr.p_filesz,
					      ELF_T_NHDR);
      if (likely (notes != NULL))
	{
	  size_t pos = 0;
	  GElf_Nhdr nhdr;
	  size_t name_pos;
	  size_t desc_pos;
	  while ((pos = gelf_getnote (notes, pos, &nhdr,
				      &name_pos, &desc_pos)) > 0)
	    if (nhdr.n_type == NT_AUXV
		&& nhdr.n_namesz == sizeof "CORE"
		&& !memcmp (notes->d_buf + name_pos, "CORE", sizeof "CORE"))
	      {
		auxv = notes->d_buf + desc_pos;
		auxv_size = nhdr.n_descsz;
		break;
	      }
	}
    }

  /* Now we have NT_AUXV contents.  From here on this processing could be
     used for a live process with auxv read from /proc.  */

  return dwfl_link_map_report (dwfl, auxv, auxv_size,
			       dwfl_elf_phdr_memory_callback, elf);
}
INTDEF (dwfl_core_file_report)