auxprogs/getoff.c

   1 /*
   2    This file is part of Valgrind, a dynamic binary instrumentation
   3    framework.
   4
   5    Copyright (C) 2014-2017 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, see <http://www.gnu.org/licenses/>.
  19
  20    The GNU General Public License is contained in the file COPYING.
  21 */
  22
  23 /* This file is used to generate target executable(s) getoff-<platform>
  24    In a bi-arch setup, this is used to build 2 executables
  25    (for the primary and secondary platforms).
  26
  27    This program uses user space libraries to retrieve some platform
  28    dependent offsets needed for Valgrind core, but that cannot (easily)
  29    be retrieved by Valgrind core.
  30
  31    This is currently used only for handling the gdbsrv QGetTlsAddr query :
  32    it only computes and outputs lm_modid_offset in struct link_map
  33    of the dynamic linker. In theory, we should also compute the offset needed
  34    to get the dtv from the thread register/pointer/...
  35    Currently, the various valgrind-low-xxxxxx.c files are hardcoding this
  36    offset as it is deemed (?) stable, and there is no clear way how to
  37    compute this dtv offset.
  38
  39    The getoff-<platform> executable will be launched automatically by
  40    Valgrind gdbserver when the first QGetTlsAddr query is retrieved.
  41
  42    On plaforms that do not support __thread and/or that do not provide
  43    dlinfo RTLD_DI_TLS_MODID, this executable produces no output. */
  44
  45 #ifndef _GNU_SOURCE
  46 #define _GNU_SOURCE
  47 #endif
  48 #include <config.h>
  49
  50 #include <assert.h>
  51 #include <errno.h>
  52 #include <stdlib.h>
  53 #include <stdio.h>
  54 #include <string.h>
  55
  56 #ifdef HAVE_DLINFO_RTLD_DI_TLS_MODID
  57 #include <link.h>
  58 #include <dlfcn.h>
  59 #endif
  60
  61 /* true if arg matches the provided option */
  62 static
  63 int is_opt(char* arg, const char *option)
  64 {
  65    int option_len = strlen(option);
  66    if (option[option_len-1] == '=')
  67       return (0 == strncmp(option, arg, option_len));
  68    else
  69       return (0 == strcmp(option, arg));
  70 }
  71
  72 static int verbose = 0;
  73
  74 static
  75 void usage (char* progname)
  76 {
  77    fprintf(stderr,
  78 "Usage: %s [--help] [-h] [-v] [-o <outputfile>]\n"
  79 "Outputs various user space offsets\n"
  80 "By default, outputs on stdout.\n"
  81 "Use -o to output to <outputfile>\n"
  82 "-v : be more verbose\n",
  83 progname);
  84
  85 }
  86
  87 int main (int argc, char** argv)
  88 {
  89    int i;
  90    FILE *outputfile;
  91    int nr_errors = 0;
  92
  93    outputfile = stdout;
  94
  95    i = 1;
  96    while (i < argc) {
  97       if (is_opt(argv[i], "--help") || is_opt(argv[i], "-h")) {
  98          usage(argv[0]);
  99          exit(0);
 100       } else if (is_opt(argv[i], "-v")) {
 101          verbose++;
 102       } else if (is_opt(argv[i], "-o")) {
 103          if (i+1 == argc) {
 104             fprintf(stderr,
 105                     "missing output file for -o option\n"
 106                     "Use --help for more information.\n");
 107             exit (1);
 108          }
 109          i++;
 110          outputfile = fopen(argv[i], "w");
 111          if (outputfile == NULL) {
 112             fprintf(stderr, "Could not fopen %s in write mode\n", argv[i]);
 113             perror ("fopen output file failed");
 114             exit (1);
 115          }
 116       } else {
 117          fprintf (stderr,
 118                   "unknown or invalid argument %s\n"
 119                   "Use --help for more information.\n",
 120                   argv[i]);
 121          exit(1);
 122       }
 123       i++;
 124    }
 125
 126 #ifdef HAVE_DLINFO_RTLD_DI_TLS_MODID
 127    /* Compute offset of lm_modid in struct link_map.
 128       This is needed to support QGetTlsAddr gdbsrv query.
 129       Computation is done using an ugly hack, but less ugly than
 130       hardcoding the offset depending on the glibc version and
 131       platform.
 132       The below works, based the assumption that RTLD_DI_TLS_MODID
 133       just access and returns directly the field in the dummy
 134       link_map structure we have prepared.
 135
 136       If glibc debug info is installed on your system, you can
 137       also find this offset by doing in GDB:
 138           p &((struct link_map*)0x0)->l_tls_modid
 139       (see also coregrind/m_gdbserver/valgrind_low.h target_get_dtv
 140        comments).
 141    */
 142    {
 143       #define MAX_LINKMAP_WORDS 10000
 144       size_t dummy_link_map[MAX_LINKMAP_WORDS];
 145       size_t off;
 146       size_t modid_offset;
 147       for (off = 0; off < MAX_LINKMAP_WORDS; off++)
 148          dummy_link_map[off] = off;
 149       if (dlinfo ((void*)dummy_link_map, RTLD_DI_TLS_MODID,
 150                   &modid_offset) == 0) {
 151          assert(modid_offset >= 0 && modid_offset < MAX_LINKMAP_WORDS);
 152          fprintf(outputfile,
 153                  "lm_modid_offset 0x%zx\n", modid_offset*sizeof(size_t));
 154       } else {
 155          fprintf(stderr,
 156                  "Error computing lm_modid_offset.\n"
 157                  "dlinfo error %s\n", dlerror());
 158          nr_errors++;
 159       }
 160       #undef MAX_LINKMAP_WORDS
 161    }
 162
 163    if (outputfile != stdout)
 164       if (fclose (outputfile) != 0) {
 165          perror ("fclose output file failed\n");
 166          nr_errors++;
 167       }
 168 #else
 169    if (verbose)
 170       fprintf(stderr,
 171               "cannot compute lm_modid_offset.\n"
 172               "configure did not define HAVE_DLINFO_RTLD_DI_TLS_MODID.\n");
 173 #endif
 174
 175    if (nr_errors == 0)
 176       exit(0);
 177    else
 178       exit(1);
 179 }