dwfl_build_id_find_elf.c revision de2ed97f33139af5c7a0811e4ec66fc896a13cf2 
1/* Find an ELF file for a module from its build ID.
2   Copyright (C) 2007-2010 Red Hat, Inc.
3   This file is part of elfutils.
4
5   This file is free software; you can redistribute it and/or modify
6   it under the terms of either
7
8     * the GNU Lesser General Public License as published by the Free
9       Software Foundation; either version 3 of the License, or (at
10       your option) any later version
11
12   or
13
14     * the GNU General Public License as published by the Free
15       Software Foundation; either version 2 of the License, or (at
16       your option) any later version
17
18   or both in parallel, as here.
19
20   elfutils is distributed in the hope that it will be useful, but
21   WITHOUT ANY WARRANTY; without even the implied warranty of
22   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
23   General Public License for more details.
24
25   You should have received copies of the GNU General Public License and
26   the GNU Lesser General Public License along with this program.  If
27   not, see <http://www.gnu.org/licenses/>.  */
28
29#include "libdwflP.h"
30#include <inttypes.h>
31#include <fcntl.h>
32#include <unistd.h>
33
34
35int
36internal_function
37__libdwfl_open_by_build_id (Dwfl_Module *mod, bool debug, char **file_name)
38{
39  /* If *FILE_NAME was primed into the module, leave it there
40     as the fallback when we have nothing to offer.  */
41  errno = 0;
42  if (mod->build_id_len <= 0)
43    return -1;
44
45  const size_t id_len = mod->build_id_len;
46  const uint8_t *id = mod->build_id_bits;
47
48  /* Search debuginfo_path directories' .build-id/ subdirectories.  */
49
50  char id_name[sizeof "/.build-id/" + 1 + id_len * 2 + sizeof ".debug" - 1];
51  strcpy (id_name, "/.build-id/");
52  int n = snprintf (&id_name[sizeof "/.build-id/" - 1],
53		    4, "%02" PRIx8 "/", (uint8_t) id[0]);
54  assert (n == 3);
55  for (size_t i = 1; i < id_len; ++i)
56    {
57      n = snprintf (&id_name[sizeof "/.build-id/" - 1 + 3 + (i - 1) * 2],
58		    3, "%02" PRIx8, (uint8_t) id[i]);
59      assert (n == 2);
60    }
61  if (debug)
62    strcpy (&id_name[sizeof "/.build-id/" - 1 + 3 + (id_len - 1) * 2],
63	    ".debug");
64
65  const Dwfl_Callbacks *const cb = mod->dwfl->callbacks;
66  char *path = strdupa ((cb->debuginfo_path ? *cb->debuginfo_path : NULL)
67			?: DEFAULT_DEBUGINFO_PATH);
68
69  int fd = -1;
70  char *dir;
71  while (fd < 0 && (dir = strsep (&path, ":")) != NULL)
72    {
73      if (dir[0] == '+' || dir[0] == '-')
74	++dir;
75
76      /* Only absolute directory names are useful to us.  */
77      if (dir[0] != '/')
78	continue;
79
80      size_t dirlen = strlen (dir);
81      char *name = malloc (dirlen + sizeof id_name);
82      if (unlikely (name == NULL))
83	break;
84      memcpy (mempcpy (name, dir, dirlen), id_name, sizeof id_name);
85
86      fd = TEMP_FAILURE_RETRY (open64 (name, O_RDONLY));
87      if (fd >= 0)
88	{
89	  if (*file_name != NULL)
90	    free (*file_name);
91	  *file_name = canonicalize_file_name (name);
92	  if (*file_name == NULL)
93	    {
94	      *file_name = name;
95	      name = NULL;
96	    }
97	}
98      free (name);
99    }
100
101  /* If we simply found nothing, clear errno.  If we had some other error
102     with the file, report that.  Possibly this should treat other errors
103     like ENOENT too.  But ignoring all errors could mask some that should
104     be reported.  */
105  if (fd < 0 && errno == ENOENT)
106    errno = 0;
107
108  return fd;
109}
110
111int
112dwfl_build_id_find_elf (Dwfl_Module *mod,
113			void **userdata __attribute__ ((unused)),
114			const char *modname __attribute__ ((unused)),
115			Dwarf_Addr base __attribute__ ((unused)),
116			char **file_name, Elf **elfp)
117{
118  *elfp = NULL;
119  int fd = __libdwfl_open_by_build_id (mod, false, file_name);
120  if (fd >= 0)
121    {
122      Dwfl_Error error = __libdw_open_file (&fd, elfp, true, false);
123      if (error != DWFL_E_NOERROR)
124	__libdwfl_seterrno (error);
125      else if (__libdwfl_find_build_id (mod, false, *elfp) == 2)
126	{
127	  /* This is a backdoor signal to short-circuit the ID refresh.  */
128	  mod->main.valid = true;
129	  return fd;
130	}
131      else
132	{
133	  /* This file does not contain the ID it should!  */
134	  elf_end (*elfp);
135	  *elfp = NULL;
136	  close (fd);
137	  fd = -1;
138	}
139      free (*file_name);
140      *file_name = NULL;
141    }
142  else if (errno == 0 && mod->build_id_len > 0)
143    /* Setting this with no file yet loaded is a marker that
144       the build ID is authoritative even if we also know a
145       putative *FILE_NAME.  */
146    mod->main.valid = true;
147
148  return fd;
149}
150INTDEF (dwfl_build_id_find_elf)
151