elfutils/libdwfl/offline.c

/* Recover relocatibility for addresses computed from debug information.
   Copyright (C) 2005-2009, 2012 Red Hat, Inc.
   Copyright (C) 2022 Mark J. Wielaard <[email protected]>
   Copyright (C) 2022 Google LLC
   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 "libelfP.h"
#include "libdwflP.h"
#include <fcntl.h>

/* Since dwfl_report_elf lays out the sections already, this will only be
   called when the section headers of the debuginfo file are being
   consulted instead, or for the section placed at 0.  With binutils
   strip-to-debug, the symbol table is in the debuginfo file and relocation
   looks there.  */
int
dwfl_offline_section_address (Dwfl_Module *mod,
			      void **userdata __attribute__ ((unused)),
			      const char *modname __attribute__ ((unused)),
			      Dwarf_Addr base __attribute__ ((unused)),
			      const char *secname __attribute__ ((unused)),
			      Elf32_Word shndx,
			      const GElf_Shdr *shdr __attribute__ ((unused)),
			      Dwarf_Addr *addr)
{
  if (mod->e_type != ET_REL
      || shdr->sh_addr != 0
      || !(shdr->sh_flags & SHF_ALLOC)
      || shndx == 0)
    return -1;

  if (mod->debug.elf == NULL)
    /* We are only here because sh_addr is zero even though layout is complete.
       The first section in the first file under -e is placed at 0.  */
    return 0;

  /* The section numbers might not match between the two files.
     The best we can rely on is the order of SHF_ALLOC sections.  */

  Elf_Scn *ourscn = elf_getscn (mod->debug.elf, shndx);
  Elf_Scn *scn = NULL;
  uint_fast32_t skip_alloc = 0;
  while ((scn = elf_nextscn (mod->debug.elf, scn)) != ourscn)
    {
      assert (scn != NULL);
      GElf_Shdr shdr_mem;
      GElf_Shdr *sh = gelf_getshdr (scn, &shdr_mem);
      if (unlikely (sh == NULL))
	return -1;
      if (sh->sh_flags & SHF_ALLOC)
	++skip_alloc;
    }

  scn = NULL;
  while ((scn = elf_nextscn (mod->main.elf, scn)) != NULL)
    {
      GElf_Shdr shdr_mem;
      GElf_Shdr *main_shdr = gelf_getshdr (scn, &shdr_mem);
      if (unlikely (main_shdr == NULL))
	return -1;
      if ((main_shdr->sh_flags & SHF_ALLOC) && skip_alloc-- == 0)
	{
	  assert (main_shdr->sh_flags == shdr->sh_flags);
	  *addr = main_shdr->sh_addr;
	  return 0;
	}
    }

  /* This should never happen.  */
  return -1;
}
INTDEF (dwfl_offline_section_address)

/* Forward declarations.  */
static Dwfl_Module *process_elf (Dwfl *dwfl, const char *name,
				 const char *file_name, int fd, Elf *elf);
static Dwfl_Module *process_archive (Dwfl *dwfl, const char *name,
				     const char *file_name, int fd, Elf *elf,
				     int (*predicate) (const char *module,
						       const char *file));

/* Report one module for an ELF file, or many for an archive.
   Always consumes ELF and FD.  */
static Dwfl_Module *
process_file (Dwfl *dwfl, const char *name, const char *file_name, int fd,
	      Elf *elf, int (*predicate) (const char *module,
					  const char *file))
{
  switch (elf_kind (elf))
    {
    default:
    case ELF_K_NONE:
      __libdwfl_seterrno (elf == NULL ? DWFL_E_LIBELF : DWFL_E_BADELF);
      return NULL;

    case ELF_K_ELF:
      return process_elf (dwfl, name, file_name, fd, elf);

    case ELF_K_AR:
      return process_archive (dwfl, name, file_name, fd, elf, predicate);
    }
}

/* Report the open ELF file as a module.  Always consumes ELF and FD.  */
static Dwfl_Module *
process_elf (Dwfl *dwfl, const char *name, const char *file_name, int fd,
	     Elf *elf)
{
  Dwfl_Module *mod = __libdwfl_report_elf (dwfl, name, file_name, fd, elf,
					   dwfl->offline_next_address, true,
					   false);
  if (mod != NULL)
    {
      /* If this is an ET_EXEC file with fixed addresses, the address range
	 it consumed may or may not intersect with the arbitrary range we
	 will use for relocatable modules.  Make sure we always use a free
	 range for the offline allocations.  If this module did use
	 offline_next_address, it may have rounded it up for the module's
	 alignment requirements.  */
      if ((dwfl->offline_next_address >= mod->low_addr
	   || mod->low_addr - dwfl->offline_next_address < OFFLINE_REDZONE)
	  && dwfl->offline_next_address < mod->high_addr + OFFLINE_REDZONE)
	dwfl->offline_next_address = mod->high_addr + OFFLINE_REDZONE;

      /* Don't keep the file descriptor around.  */
      if (mod->main.fd != -1 && elf_cntl (mod->main.elf, ELF_C_FDREAD) == 0)
	{
	  /* Grab the path in case we want to report this file as
	     Dwarf later.  */
	  mod->elfpath = __libdw_elfpath (mod->main.fd);
	  close (mod->main.fd);
	  mod->main.fd = -1;
	}
    }

  return mod;
}

/* Always consumes MEMBER.  Returns elf_next result on success.
   For errors returns ELF_C_NULL with *MOD set to null.  */
static Elf_Cmd
process_archive_member (Dwfl *dwfl, const char *name, const char *file_name,
			int (*predicate) (const char *module, const char *file),
			int fd, Elf *member, Dwfl_Module **mod)
{
  const Elf_Arhdr *h = elf_getarhdr (member);
  if (unlikely (h == NULL))
    {
      __libdwfl_seterrno (DWFL_E_LIBELF);
    fail:
      elf_end (member);
      *mod = NULL;
      return ELF_C_NULL;
    }

  if (!strcmp (h->ar_name, "/") || !strcmp (h->ar_name, "//")
      || !strcmp (h->ar_name, "/SYM64/"))
    {
    skip:;
      /* Skip this and go to the next.  */
      Elf_Cmd result = elf_next (member);
      elf_end (member);
      return result;
    }

  char *member_name;
  if (unlikely (asprintf (&member_name, "%s(%s)", file_name, h->ar_name) < 0))
    {
    nomem:
      __libdwfl_seterrno (DWFL_E_NOMEM);
      elf_end (member);
      *mod = NULL;
      return ELF_C_NULL;
    }

  char *module_name = NULL;
  if (name == NULL || name[0] == '\0')
    name = h->ar_name;
  else if (unlikely (asprintf (&module_name, "%s:%s", name, h->ar_name) < 0))
    {
      free (member_name);
      goto nomem;
    }
  else
    name = module_name;

  if (predicate != NULL)
    {
      /* Let the predicate decide whether to use this one.  */
      int want = (*predicate) (name, member_name);
      if (want <= 0)
	{
	  free (member_name);
	  free (module_name);
	  if (unlikely (want < 0))
	    {
	      __libdwfl_seterrno (DWFL_E_CB);
	      goto fail;
	    }
	  goto skip;
	}
    }

  /* We let __libdwfl_report_elf cache the fd in mod->main.fd,
     though it's the same fd for all the members.
     On module teardown we will close it only on the last Elf reference.  */
  *mod = process_file (dwfl, name, member_name, fd, member, predicate);
  free (member_name);
  free (module_name);

  if (*mod == NULL)
    {
      elf_end (member);
      return ELF_C_NULL;
    }

  /* Advance the archive-reading offset for the next iteration.  */
  return elf_next (member);
}

/* Report each member of the archive as its own module.  */
static Dwfl_Module *
process_archive (Dwfl *dwfl, const char *name, const char *file_name, int fd,
		 Elf *archive,
		 int (*predicate) (const char *module, const char *file))

{
  Dwfl_Module *mod = NULL;
  /* elf_begin supports opening archives even with fd == -1 passed.  */
  Elf *member = elf_begin (fd, archive->cmd, archive);
  if (unlikely (member == NULL)) /* Empty archive.  */
    {
      __libdwfl_seterrno (DWFL_E_BADELF);
      return NULL;
    }

  while (process_archive_member (dwfl, name, file_name, predicate,
				 fd, member, &mod) != ELF_C_NULL)
    member = elf_begin (fd, archive->cmd, archive);

  /* We can drop the archive Elf handle even if we're still using members
     in live modules.  When the last module's elf_end on a member returns
     zero, that module will close FD.  If no modules survived the predicate,
     we are all done with the file right here.  */
  if (mod != NULL		/* If no modules, caller will clean up.  */
      && elf_end (archive) == 0)
    close (fd);

  return mod;
}

Dwfl_Module *
internal_function
__libdwfl_report_offline (Dwfl *dwfl, const char *name,
			  const char *file_name, int fd, bool closefd,
			  int (*predicate) (const char *module,
					    const char *file))
{
  Elf *elf;
  Dwfl_Error error = __libdw_open_file (&fd, &elf, closefd, true);
  if (error != DWFL_E_NOERROR)
    {
      __libdwfl_seterrno (error);
      return NULL;
    }
  Dwfl_Module *mod = process_file (dwfl, name, file_name, fd, elf, predicate);
  if (mod == NULL)
    {
      elf_end (elf);
      if (closefd)
	close (fd);
    }
  return mod;
}

Dwfl_Module *
dwfl_report_offline (Dwfl *dwfl, const char *name,
		     const char *file_name, int fd)
{
  if (dwfl == NULL)
    return NULL;

  bool closefd = false;
  if (fd < 0)
    {
      closefd = true;
      fd = open (file_name, O_RDONLY);
      if (fd < 0)
	{
	  __libdwfl_seterrno (DWFL_E_ERRNO);
	  return NULL;
	}
    }

  return __libdwfl_report_offline (dwfl, name, file_name, fd, closefd, NULL);
}
INTDEF (dwfl_report_offline)

Dwfl_Module *
dwfl_report_offline_memory (Dwfl *dwfl, const char *name,
			    const char *file_name, char *data, size_t size)
{
  if (dwfl == NULL)
    return NULL;

  Elf *elf;
  Dwfl_Error error = __libdw_open_elf_memory (data, size, &elf, true);
  if (error != DWFL_E_NOERROR)
    {
      __libdwfl_seterrno (error);
      return NULL;
    }
  /* It is ok to pass fd == -1 here, because libelf uses it as a value for
     "no file opened" and supports working with files without fd, thanks to
     the existence of the elf_memory function.  */
  Dwfl_Module *mod = process_file (dwfl, name, file_name, -1, elf, NULL);
  if (mod == NULL)
    elf_end (elf);
  return mod;
}
INTDEF (dwfl_report_offline_memory)