libdwfl/find-debuginfo.c - platform/external/elfutils.git - Git at Google

 /* Standard find_debuginfo callback for libdwfl.
    Copyright (C) 2005-2010, 2014, 2015, 2019 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 <stdio.h>
 #include <fcntl.h>
 #include <unistd.h>
 #include <sys/stat.h>
 #include "system.h"


 /* Try to open [DIR/][SUBDIR/]DEBUGLINK, return file descriptor or -1.
    On success, *DEBUGINFO_FILE_NAME has the malloc'd name of the open file.  */
 static int
 try_open (const struct stat *main_stat,
 	  const char *dir, const char *subdir, const char *debuglink,
 	  char **debuginfo_file_name)
 {
   char *fname;
   if (dir == NULL && subdir == NULL)
     {
       fname = strdup (debuglink);
       if (unlikely (fname == NULL))
 	return -1;
     }
   else if ((subdir == NULL ? asprintf (&fname, "%s/%s", dir, debuglink)
 	    : dir == NULL ? asprintf (&fname, "%s/%s", subdir, debuglink)
 	    : asprintf (&fname, "%s/%s/%s", dir, subdir, debuglink)) < 0)
     return -1;

   struct stat st;
   int fd = TEMP_FAILURE_RETRY (open (fname, O_RDONLY));
   if (fd < 0)
     free (fname);
   else if (fstat (fd, &st) == 0
 	   && st.st_ino == main_stat->st_ino
 	   && st.st_dev == main_stat->st_dev)
     {
       /* This is the main file by another name.  Don't look at it again.  */
       free (fname);
       close (fd);
       errno = ENOENT;
       fd = -1;
     }
   else
     *debuginfo_file_name = fname;

   return fd;
 }

 /* Return true iff the FD's contents CRC matches DEBUGLINK_CRC.  */
 static inline bool
 check_crc (int fd, GElf_Word debuglink_crc)
 {
   uint32_t file_crc;
   return (__libdwfl_crc32_file (fd, &file_crc) == 0
 	  && file_crc == debuglink_crc);
 }

 static bool
 validate (Dwfl_Module *mod, int fd, bool check, GElf_Word debuglink_crc)
 {
   /* For alt debug files always check the build-id from the Dwarf and alt.  */
   if (mod->dw != NULL)
     {
       bool valid = false;
       const void *build_id;
       const char *altname;
       ssize_t build_id_len = INTUSE(dwelf_dwarf_gnu_debugaltlink) (mod->dw,
 								   &altname,
 								   &build_id);
       if (build_id_len > 0)
 	{
 	  /* We need to open an Elf handle on the file so we can check its
 	     build ID note for validation.  Backdoor the handle into the
 	     module data structure since we had to open it early anyway.  */
 	  Dwfl_Error error = __libdw_open_file (&fd, &mod->alt_elf,
 						false, false);
 	  if (error != DWFL_E_NOERROR)
 	    __libdwfl_seterrno (error);
 	  else
 	    {
 	      const void *alt_build_id;
 	      ssize_t alt_len = INTUSE(dwelf_elf_gnu_build_id) (mod->alt_elf,
 								&alt_build_id);
 	      if (alt_len > 0 && alt_len == build_id_len
 		  && memcmp (build_id, alt_build_id, alt_len) == 0)
 		valid = true;
 	      else
 		{
 		  /* A mismatch!  */
 		  elf_end (mod->alt_elf);
 		  mod->alt_elf = NULL;
 		  close (fd);
 		  fd = -1;
 		}
 	    }
 	}
       return valid;
     }

   /* If we have a build ID, check only that.  */
   if (mod->build_id_len > 0)
     {
       /* We need to open an Elf handle on the file so we can check its
 	 build ID note for validation.  Backdoor the handle into the
 	 module data structure since we had to open it early anyway.  */

       mod->debug.valid = false;
       Dwfl_Error error = __libdw_open_file (&fd, &mod->debug.elf, false, false);
       if (error != DWFL_E_NOERROR)
 	__libdwfl_seterrno (error);
       else if (likely (__libdwfl_find_build_id (mod, false,
 						mod->debug.elf) == 2))
 	/* Also backdoor the gratuitous flag.  */
 	mod->debug.valid = true;
       else
 	{
 	  /* A mismatch!  */
 	  elf_end (mod->debug.elf);
 	  mod->debug.elf = NULL;
 	  close (fd);
 	  fd = -1;
 	}

       return mod->debug.valid;
     }

   return !check || check_crc (fd, debuglink_crc);
 }

 static int
 find_debuginfo_in_path (Dwfl_Module *mod, const char *file_name,
 			const char *debuglink_file, GElf_Word debuglink_crc,
 			char **debuginfo_file_name)
 {
   bool cancheck = debuglink_crc != (GElf_Word) 0;

   const char *file_basename = file_name == NULL ? NULL : basename (file_name);
   char *localname = NULL;

   /* We invent a debuglink .debug name if NULL, but then want to try the
      basename too.  */
   bool debuglink_null = debuglink_file == NULL;
   if (debuglink_null)
     {
       /* For a alt debug multi file we need a name, for a separate debug
 	 name we may be able to fall back on file_basename.debug.  */
       if (file_basename == NULL || mod->dw != NULL)
 	{
 	  errno = 0;
 	  return -1;
 	}

       size_t len = strlen (file_basename);
       localname = malloc (len + sizeof ".debug");
       if (unlikely (localname == NULL))
 	return -1;
       memcpy (localname, file_basename, len);
       memcpy (&localname[len], ".debug", sizeof ".debug");
       debuglink_file = localname;
       cancheck = false;
     }

   /* Look for a file named DEBUGLINK_FILE in the directories
      indicated by the debug directory path setting.  */

   const Dwfl_Callbacks *const cb = mod->dwfl->callbacks;
   char *localpath = strdup ((cb->debuginfo_path ? *cb->debuginfo_path : NULL)
 			    ?: DEFAULT_DEBUGINFO_PATH);
   if (unlikely (localpath == NULL))
     {
       free (localname);
       return -1;
     }

   /* A leading - or + in the whole path sets whether to check file CRCs.  */
   bool defcheck = true;
   char *path = localpath;
   if (path[0] == '-' || path[0] == '+')
     {
       defcheck = path[0] == '+';
       ++path;
     }

   /* XXX dev/ino should be cached in struct dwfl_file.  */
   struct stat main_stat;
   if (unlikely ((mod->main.fd != -1 ? fstat (mod->main.fd, &main_stat)
 		 : file_name != NULL ? stat (file_name, &main_stat)
 		 : -1) < 0))
     {
       main_stat.st_dev = 0;
       main_stat.st_ino = 0;
     }

   char *file_dirname = (file_basename == file_name ? NULL
 			: strndup (file_name, file_basename - 1 - file_name));
   if (file_basename != file_name && file_dirname == NULL)
     {
       free (localpath);
       free (localname);
       return -1;
     }
   char *p;
   while ((p = strsep (&path, ":")) != NULL)
     {
       /* A leading - or + says whether to check file CRCs for this element.  */
       bool check = defcheck;
       if (*p == '+' || *p == '-')
 	check = *p++ == '+';
       check = check && cancheck;

       /* Try the basename too, if we made up the debuglink name and this
 	 is not the main directory.  */
       bool try_file_basename;

       const char *dir, *subdir, *file;
       switch (p[0])
 	{
 	case '\0':
 	  /* An empty entry says to try the main file's directory.  */
 	  dir = file_dirname;
 	  subdir = NULL;
 	  file = debuglink_file;
 	  try_file_basename = false;
 	  break;
 	case '/':
 	  /* An absolute path says to look there for a subdirectory
 	     named by the main file's absolute directory.  This cannot
 	     be applied to a relative file name.  For alt debug files
 	     it means to look for the basename file in that dir or the
 	     .dwz subdir (see below).  */
 	  if (mod->dw == NULL
 	      && (file_dirname == NULL || file_dirname[0] != '/'))
 	    continue;
 	  dir = p;
 	  if (mod->dw == NULL)
 	    {
 	      subdir = file_dirname;
 	      /* We want to explore all sub-subdirs.  Chop off one slash
 		 at a time.  */
 	    explore_dir:
 	      subdir = strchr (subdir, '/');
 	      if (subdir != NULL)
 		subdir = subdir + 1;
 	      if (subdir && *subdir == 0)
 		continue;
 	      file = debuglink_file;
 	    }
 	  else
 	    {
 	      subdir = NULL;
 	      file = basename (debuglink_file);
 	    }
 	  try_file_basename = debuglink_null;
 	  break;
 	default:
 	  /* A relative path says to try a subdirectory of that name
 	     in the main file's directory.  */
 	  dir = file_dirname;
 	  subdir = p;
 	  file = debuglink_file;
 	  try_file_basename = debuglink_null;
 	  break;
 	}

       char *fname = NULL;
       int fd = try_open (&main_stat, dir, subdir, file, &fname);
       if (fd < 0 && try_file_basename)
 	fd = try_open (&main_stat, dir, subdir, file_basename, &fname);
       if (fd < 0)
 	switch (errno)
 	  {
 	  case ENOENT:
 	  case ENOTDIR:
 	    /* If we are looking for the alt file also try the .dwz subdir.
 	       But only if this is the empty or absolute path.  */
 	    if (mod->dw != NULL && (p[0] == '\0' || p[0] == '/'))
 	      {
 		fd = try_open (&main_stat, dir, ".dwz",
 			       basename (file), &fname);
 		if (fd < 0)
 		  {
 		    if (errno != ENOENT && errno != ENOTDIR)
 		      goto fail_free;
 		    else
 		      continue;
 		  }
 		break;
 	      }
 	    /* If possible try again with a sub-subdir.  */
 	    if (mod->dw == NULL && subdir)
 	      goto explore_dir;
 	    continue;
 	  default:
 	    goto fail_free;
 	  }
       if (validate (mod, fd, check, debuglink_crc))
 	{
 	  free (localpath);
 	  free (localname);
 	  free (file_dirname);
 	  *debuginfo_file_name = fname;
 	  return fd;
 	}
       free (fname);
       close (fd);
     }

   /* No dice.  */
   errno = 0;
 fail_free:
   free (localpath);
   free (localname);
   free (file_dirname);
   return -1;
 }

 int
 dwfl_standard_find_debuginfo (Dwfl_Module *mod,
 			      void **userdata __attribute__ ((unused)),
 			      const char *modname __attribute__ ((unused)),
 			      GElf_Addr base __attribute__ ((unused)),
 			      const char *file_name,
 			      const char *debuglink_file,
 			      GElf_Word debuglink_crc,
 			      char **debuginfo_file_name)
 {
   if (mod == NULL)
     return -1;

   /* First try by build ID if we have one.  If that succeeds or fails
      other than just by finding nothing, that's all we do.  */
   const unsigned char *bits = NULL;
   GElf_Addr vaddr;
   int bits_len;
   if ((bits_len = INTUSE(dwfl_module_build_id) (mod, &bits, &vaddr)) > 0)
     {
       /* Dropping most arguments means we cannot rely on them in
 	 dwfl_build_id_find_debuginfo.  But leave it that way since
 	 some user code out there also does this, so we'll have to
 	 handle it anyway.  */
       int fd = INTUSE(dwfl_build_id_find_debuginfo) (mod,
 						     NULL, NULL, 0,
 						     NULL, NULL, 0,
 						     debuginfo_file_name);

       /* Did the build_id callback find something or report an error?
          Then we are done.  Otherwise fallback on path based search.  */
       if (fd >= 0
 	  || (mod->dw == NULL && mod->debug.elf != NULL)
 	  || (mod->dw != NULL && mod->alt_elf != NULL)
 	  || errno != 0)
 	return fd;
     }

   /* Failing that, search the path by name.  */
   int fd = find_debuginfo_in_path (mod, file_name,
 				   debuglink_file, debuglink_crc,
 				   debuginfo_file_name);

   if (fd < 0 && errno == 0 && file_name != NULL)
     {
       /* If FILE_NAME is a symlink, the debug file might be associated
 	 with the symlink target name instead.  */

       char *canon = realpath (file_name, NULL);
       if (canon != NULL && strcmp (file_name, canon))
 	fd = find_debuginfo_in_path (mod, canon,
 				     debuglink_file, debuglink_crc,
 				     debuginfo_file_name);
       free (canon);
     }

 #ifdef ENABLE_LIBDEBUGINFOD
   /* Still nothing? Try if we can use the debuginfod client.
      But note that we might be looking for the alt file.
      We use the same trick as dwfl_build_id_find_debuginfo.
      If the debug file (dw) is already set, then we must be
      looking for the altfile. But we cannot use the actual
      file/path name given as hint. We'll have to lookup the
      alt file "build-id". Because the debuginfod client only
      handles build-ids.  */
   if (fd < 0)
     {
       if (mod->dw != NULL)
 	{
 	  const char *altname;
 	  bits_len = INTUSE(dwelf_dwarf_gnu_debugaltlink) (mod->dw, &altname,
 							   (const void **)
 							   &bits);
 	}

       if (bits_len > 0)
 	fd = __libdwfl_debuginfod_find_debuginfo (mod->dwfl, bits, bits_len);
     }
 #endif

   return fd;
 }
 INTDEF (dwfl_standard_find_debuginfo)
	/* Standard find_debuginfo callback for libdwfl.
	Copyright (C) 2005-2010, 2014, 2015, 2019 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 <stdio.h>
	#include <fcntl.h>
	#include <unistd.h>
	#include <sys/stat.h>
	#include "system.h"


	/* Try to open [DIR/][SUBDIR/]DEBUGLINK, return file descriptor or -1.
	On success, DEBUGINFO_FILE_NAME has the malloc'd name of the open file. /
	static int
	try_open (const struct stat *main_stat,
	const char dir, const char subdir, const char *debuglink,
	char **debuginfo_file_name)
	{
	char *fname;
	if (dir == NULL && subdir == NULL)
	{
	fname = strdup (debuglink);
	if (unlikely (fname == NULL))
	return -1;
	}
	else if ((subdir == NULL ? asprintf (&fname, "%s/%s", dir, debuglink)
	: dir == NULL ? asprintf (&fname, "%s/%s", subdir, debuglink)
	: asprintf (&fname, "%s/%s/%s", dir, subdir, debuglink)) < 0)
	return -1;

	struct stat st;
	int fd = TEMP_FAILURE_RETRY (open (fname, O_RDONLY));
	if (fd < 0)
	free (fname);
	else if (fstat (fd, &st) == 0
	&& st.st_ino == main_stat->st_ino
	&& st.st_dev == main_stat->st_dev)
	{
	/* This is the main file by another name. Don't look at it again. */
	free (fname);
	close (fd);
	errno = ENOENT;
	fd = -1;
	}
	else
	*debuginfo_file_name = fname;

	return fd;
	}

	/* Return true iff the FD's contents CRC matches DEBUGLINK_CRC. */
	static inline bool
	check_crc (int fd, GElf_Word debuglink_crc)
	{
	uint32_t file_crc;
	return (__libdwfl_crc32_file (fd, &file_crc) == 0
	&& file_crc == debuglink_crc);
	}

	static bool
	validate (Dwfl_Module *mod, int fd, bool check, GElf_Word debuglink_crc)
	{
	/* For alt debug files always check the build-id from the Dwarf and alt. */
	if (mod->dw != NULL)
	{
	bool valid = false;
	const void *build_id;
	const char *altname;
	ssize_t build_id_len = INTUSE(dwelf_dwarf_gnu_debugaltlink) (mod->dw,
	&altname,
	&build_id);
	if (build_id_len > 0)
	{
	/* We need to open an Elf handle on the file so we can check its
	build ID note for validation. Backdoor the handle into the
	module data structure since we had to open it early anyway. */
	Dwfl_Error error = __libdw_open_file (&fd, &mod->alt_elf,
	false, false);
	if (error != DWFL_E_NOERROR)
	__libdwfl_seterrno (error);
	else
	{
	const void *alt_build_id;
	ssize_t alt_len = INTUSE(dwelf_elf_gnu_build_id) (mod->alt_elf,
	&alt_build_id);
	if (alt_len > 0 && alt_len == build_id_len
	&& memcmp (build_id, alt_build_id, alt_len) == 0)
	valid = true;
	else
	{
	/* A mismatch! */
	elf_end (mod->alt_elf);
	mod->alt_elf = NULL;
	close (fd);
	fd = -1;
	}
	}
	}
	return valid;
	}

	/* If we have a build ID, check only that. */
	if (mod->build_id_len > 0)
	{
	/* We need to open an Elf handle on the file so we can check its
	build ID note for validation. Backdoor the handle into the
	module data structure since we had to open it early anyway. */

	mod->debug.valid = false;
	Dwfl_Error error = __libdw_open_file (&fd, &mod->debug.elf, false, false);
	if (error != DWFL_E_NOERROR)
	__libdwfl_seterrno (error);
	else if (likely (__libdwfl_find_build_id (mod, false,
	mod->debug.elf) == 2))
	/* Also backdoor the gratuitous flag. */
	mod->debug.valid = true;
	else
	{
	/* A mismatch! */
	elf_end (mod->debug.elf);
	mod->debug.elf = NULL;
	close (fd);
	fd = -1;
	}

	return mod->debug.valid;
	}

	return !check \|\| check_crc (fd, debuglink_crc);
	}

	static int
	find_debuginfo_in_path (Dwfl_Module mod, const char file_name,
	const char *debuglink_file, GElf_Word debuglink_crc,
	char **debuginfo_file_name)
	{
	bool cancheck = debuglink_crc != (GElf_Word) 0;

	const char *file_basename = file_name == NULL ? NULL : basename (file_name);
	char *localname = NULL;

	/* We invent a debuglink .debug name if NULL, but then want to try the
	basename too. */
	bool debuglink_null = debuglink_file == NULL;
	if (debuglink_null)
	{
	/* For a alt debug multi file we need a name, for a separate debug
	name we may be able to fall back on file_basename.debug. */
	if (file_basename == NULL \|\| mod->dw != NULL)
	{
	errno = 0;
	return -1;
	}

	size_t len = strlen (file_basename);
	localname = malloc (len + sizeof ".debug");
	if (unlikely (localname == NULL))
	return -1;
	memcpy (localname, file_basename, len);
	memcpy (&localname[len], ".debug", sizeof ".debug");
	debuglink_file = localname;
	cancheck = false;
	}

	/* Look for a file named DEBUGLINK_FILE in the directories
	indicated by the debug directory path setting. */

	const Dwfl_Callbacks *const cb = mod->dwfl->callbacks;
	char localpath = strdup ((cb->debuginfo_path ? cb->debuginfo_path : NULL)
	?: DEFAULT_DEBUGINFO_PATH);
	if (unlikely (localpath == NULL))
	{
	free (localname);
	return -1;
	}

	/* A leading - or + in the whole path sets whether to check file CRCs. */
	bool defcheck = true;
	char *path = localpath;
	if (path[0] == '-' \|\| path[0] == '+')
	{
	defcheck = path[0] == '+';
	++path;
	}

	/* XXX dev/ino should be cached in struct dwfl_file. */
	struct stat main_stat;
	if (unlikely ((mod->main.fd != -1 ? fstat (mod->main.fd, &main_stat)
	: file_name != NULL ? stat (file_name, &main_stat)
	: -1) < 0))
	{
	main_stat.st_dev = 0;
	main_stat.st_ino = 0;
	}

	char *file_dirname = (file_basename == file_name ? NULL
	: strndup (file_name, file_basename - 1 - file_name));
	if (file_basename != file_name && file_dirname == NULL)
	{
	free (localpath);
	free (localname);
	return -1;
	}
	char *p;
	while ((p = strsep (&path, ":")) != NULL)
	{
	/* A leading - or + says whether to check file CRCs for this element. */
	bool check = defcheck;
	if (p == '+' \|\| p == '-')
	check = *p++ == '+';
	check = check && cancheck;

	/* Try the basename too, if we made up the debuglink name and this
	is not the main directory. */
	bool try_file_basename;

	const char dir, subdir, *file;
	switch (p[0])
	{
	case '\0':
	/* An empty entry says to try the main file's directory. */
	dir = file_dirname;
	subdir = NULL;
	file = debuglink_file;
	try_file_basename = false;
	break;
	case '/':
	/* An absolute path says to look there for a subdirectory
	named by the main file's absolute directory. This cannot
	be applied to a relative file name. For alt debug files
	it means to look for the basename file in that dir or the
	.dwz subdir (see below). */
	if (mod->dw == NULL
	&& (file_dirname == NULL \|\| file_dirname[0] != '/'))
	continue;
	dir = p;
	if (mod->dw == NULL)
	{
	subdir = file_dirname;
	/* We want to explore all sub-subdirs. Chop off one slash
	at a time. */
	explore_dir:
	subdir = strchr (subdir, '/');
	if (subdir != NULL)
	subdir = subdir + 1;
	if (subdir && *subdir == 0)
	continue;
	file = debuglink_file;
	}
	else
	{
	subdir = NULL;
	file = basename (debuglink_file);
	}
	try_file_basename = debuglink_null;
	break;
	default:
	/* A relative path says to try a subdirectory of that name
	in the main file's directory. */
	dir = file_dirname;
	subdir = p;
	file = debuglink_file;
	try_file_basename = debuglink_null;
	break;
	}

	char *fname = NULL;
	int fd = try_open (&main_stat, dir, subdir, file, &fname);
	if (fd < 0 && try_file_basename)
	fd = try_open (&main_stat, dir, subdir, file_basename, &fname);
	if (fd < 0)
	switch (errno)
	{
	case ENOENT:
	case ENOTDIR:
	/* If we are looking for the alt file also try the .dwz subdir.
	But only if this is the empty or absolute path. */
	if (mod->dw != NULL && (p[0] == '\0' \|\| p[0] == '/'))
	{
	fd = try_open (&main_stat, dir, ".dwz",
	basename (file), &fname);
	if (fd < 0)
	{
	if (errno != ENOENT && errno != ENOTDIR)
	goto fail_free;
	else
	continue;
	}
	break;
	}
	/* If possible try again with a sub-subdir. */
	if (mod->dw == NULL && subdir)
	goto explore_dir;
	continue;
	default:
	goto fail_free;
	}
	if (validate (mod, fd, check, debuglink_crc))
	{
	free (localpath);
	free (localname);
	free (file_dirname);
	*debuginfo_file_name = fname;
	return fd;
	}
	free (fname);
	close (fd);
	}

	/* No dice. */
	errno = 0;
	fail_free:
	free (localpath);
	free (localname);
	free (file_dirname);
	return -1;
	}

	int
	dwfl_standard_find_debuginfo (Dwfl_Module *mod,
	void **userdata __attribute__ ((unused)),
	const char *modname __attribute__ ((unused)),
	GElf_Addr base __attribute__ ((unused)),
	const char *file_name,
	const char *debuglink_file,
	GElf_Word debuglink_crc,
	char **debuginfo_file_name)
	{
	if (mod == NULL)
	return -1;

	/* First try by build ID if we have one. If that succeeds or fails
	other than just by finding nothing, that's all we do. */
	const unsigned char *bits = NULL;
	GElf_Addr vaddr;
	int bits_len;
	if ((bits_len = INTUSE(dwfl_module_build_id) (mod, &bits, &vaddr)) > 0)
	{
	/* Dropping most arguments means we cannot rely on them in
	dwfl_build_id_find_debuginfo. But leave it that way since
	some user code out there also does this, so we'll have to
	handle it anyway. */
	int fd = INTUSE(dwfl_build_id_find_debuginfo) (mod,
	NULL, NULL, 0,
	NULL, NULL, 0,
	debuginfo_file_name);

	/* Did the build_id callback find something or report an error?
	Then we are done. Otherwise fallback on path based search. */
	if (fd >= 0
	\|\| (mod->dw == NULL && mod->debug.elf != NULL)
	\|\| (mod->dw != NULL && mod->alt_elf != NULL)
	\|\| errno != 0)
	return fd;
	}

	/* Failing that, search the path by name. */
	int fd = find_debuginfo_in_path (mod, file_name,
	debuglink_file, debuglink_crc,
	debuginfo_file_name);

	if (fd < 0 && errno == 0 && file_name != NULL)
	{
	/* If FILE_NAME is a symlink, the debug file might be associated
	with the symlink target name instead. */

	char *canon = realpath (file_name, NULL);
	if (canon != NULL && strcmp (file_name, canon))
	fd = find_debuginfo_in_path (mod, canon,
	debuglink_file, debuglink_crc,
	debuginfo_file_name);
	free (canon);
	}

	#ifdef ENABLE_LIBDEBUGINFOD
	/* Still nothing? Try if we can use the debuginfod client.
	But note that we might be looking for the alt file.
	We use the same trick as dwfl_build_id_find_debuginfo.
	If the debug file (dw) is already set, then we must be
	looking for the altfile. But we cannot use the actual
	file/path name given as hint. We'll have to lookup the
	alt file "build-id". Because the debuginfod client only
	handles build-ids. */
	if (fd < 0)
	{
	if (mod->dw != NULL)
	{
	const char *altname;
	bits_len = INTUSE(dwelf_dwarf_gnu_debugaltlink) (mod->dw, &altname,
	(const void **)
	&bits);
	}

	if (bits_len > 0)
	fd = __libdwfl_debuginfod_find_debuginfo (mod->dwfl, bits, bits_len);
	}
	#endif

	return fd;
	}
	INTDEF (dwfl_standard_find_debuginfo)