auxprogs/getoff.c

   1 /*
   2    This file is part of Valgrind, a dynamic binary instrumentation
   3    framework.
   4
   5    Copyright (C) 2014-2015 Philippe Waroquiers
   6
   7    This program is free software; you can redistribute it and/or
   8    modify it under the terms of the GNU General Public License as
   9    published by the Free Software Foundation; either version 2 of the
  10    License, or (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful, but
  13    WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15    General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program; if not, write to the Free Software
  19    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  20    02111-1307, USA.
  21
  22    The GNU General Public License is contained in the file COPYING.
  23 */
  24
  25 /* This file is used to generate target executable(s) getoff-<platform>
  26    In a bi-arch setup, this is used to build 2 executables
  27    (for the primary and secondary platforms).
  28
  29    This program uses user space libraries to retrieve some platform
  30    dependent offsets needed for Valgrind core, but that cannot (easily)
  31    be retrieved by Valgrind core.
  32
  33    This is currently used only for handling the gdbsrv QGetTlsAddr query :
  34    it only computes and outputs lm_modid_offset in struct link_map
  35    of the dynamic linker. In theory, we should also compute the offset needed
  36    to get the dtv from the thread register/pointer/...
  37    Currently, the various valgrind-low-xxxxxx.c files are hardcoding this
  38    offset as it is deemed (?) stable, and there is no clear way how to
  39    compute this dtv offset.
  40
  41    The getoff-<platform> executable will be launched automatically by
  42    Valgrind gdbserver when the first QGetTlsAddr query is retrieved.
  43
  44    On plaforms that do not support __thread and/or that do not provide
  45    dlinfo RTLD_DI_TLS_MODID, this executable produces no output. */
  46
  47 #ifndef _GNU_SOURCE
  48 #define _GNU_SOURCE
  49 #endif
  50 #include <config.h>
  51
  52 #include <assert.h>
  53 #include <errno.h>
  54 #include <stdlib.h>
  55 #include <stdio.h>
  56 #include <string.h>
  57
  58 #ifdef HAVE_DLINFO_RTLD_DI_TLS_MODID
  59 #include <link.h>
  60 #include <dlfcn.h>
  61 #endif
  62
  63 /* true if arg matches the provided option */
  64 static
  65 int is_opt(char* arg, const char *option)
  66 {
  67    int option_len = strlen(option);
  68    if (option[option_len-1] == '=')
  69       return (0 == strncmp(option, arg, option_len));
  70    else
  71       return (0 == strcmp(option, arg));
  72 }
  73
  74 static int verbose = 0;
  75
  76 static
  77 void usage (char* progname)
  78 {
  79    fprintf(stderr,
  80 "Usage: %s [--help] [-h] [-v] [-o <outputfile>]\n"
  81 "Outputs various user space offsets\n"
  82 "By default, outputs on stdout.\n"
  83 "Use -o to output to <outputfile>\n"
  84 "-v : be more verbose\n",
  85 progname);
  86
  87 }
  88
  89 int main (int argc, char** argv)
  90 {
  91    int i;
  92    FILE *outputfile;
  93    int nr_errors = 0;
  94
  95    outputfile = stdout;
  96
  97    i = 1;
  98    while (i < argc) {
  99       if (is_opt(argv[i], "--help") || is_opt(argv[i], "-h")) {
 100          usage(argv[0]);
 101          exit(0);
 102       } else if (is_opt(argv[i], "-v")) {
 103          verbose++;
 104       } else if (is_opt(argv[i], "-o")) {
 105          if (i+1 == argc) {
 106             fprintf(stderr,
 107                     "missing output file for -o option\n"
 108                     "Use --help for more information.\n");
 109             exit (1);
 110          }
 111          i++;
 112          outputfile = fopen(argv[i], "w");
 113          if (outputfile == NULL) {
 114             fprintf(stderr, "Could not fopen %s in write mode\n", argv[i]);
 115             perror ("fopen output file failed");
 116             exit (1);
 117          }
 118       } else {
 119          fprintf (stderr,
 120                   "unknown or invalid argument %s\n"
 121                   "Use --help for more information.\n",
 122                   argv[i]);
 123          exit(1);
 124       }
 125       i++;
 126    }
 127
 128 #ifdef HAVE_DLINFO_RTLD_DI_TLS_MODID
 129    /* Compute offset of lm_modid in struct link_map.
 130       This is needed to support QGetTlsAddr gdbsrv query.
 131       Computation is done using an ugly hack, but less ugly than
 132       hardcoding the offset depending on the glibc version and
 133       platform.
 134       The below works, based the assumption that RTLD_DI_TLS_MODID
 135       just access and returns directly the field in the dummy
 136       link_map structure we have prepared.
 137
 138       If glibc debug info is installed on your system, you can
 139       also find this offset by doing in GDB:
 140           p &((struct link_map*)0x0)->l_tls_modid
 141       (see also coregrind/m_gdbserver/valgrind_low.h target_get_dtv
 142        comments).
 143    */
 144    {
 145       #define MAX_LINKMAP_WORDS 10000
 146       size_t dummy_link_map[MAX_LINKMAP_WORDS];
 147       size_t off;
 148       size_t modid_offset;
 149       for (off = 0; off < MAX_LINKMAP_WORDS; off++)
 150          dummy_link_map[off] = off;
 151       if (dlinfo ((void*)dummy_link_map, RTLD_DI_TLS_MODID,
 152                   &modid_offset) == 0) {
 153          assert(modid_offset >= 0 && modid_offset < MAX_LINKMAP_WORDS);
 154          fprintf(outputfile,
 155                  "lm_modid_offset 0x%zx\n", modid_offset*sizeof(size_t));
 156       } else {
 157          fprintf(stderr,
 158                  "Error computing lm_modid_offset.\n"
 159                  "dlinfo error %s\n", dlerror());
 160          nr_errors++;
 161       }
 162       #undef MAX_LINKMAP_WORDS
 163    }
 164
 165    if (outputfile != stdout)
 166       if (fclose (outputfile) != 0) {
 167          perror ("fclose output file failed\n");
 168          nr_errors++;
 169       }
 170 #else
 171    if (verbose)
 172       fprintf(stderr,
 173               "cannot compute lm_modid_offset.\n"
 174               "configure did not define HAVE_DLINFO_RTLD_DI_TLS_MODID.\n");
 175 #endif
 176
 177    if (nr_errors == 0)
 178       exit(0);
 179    else
 180       exit(1);
 181 }