debug/segfault.c

   1 /* Catch segmentation faults and print backtrace.
   2    Copyright (C) 1998-2020 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1998.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <https://www.gnu.org/licenses/>.  */
  19
  20 #include <alloca.h>
  21 #include <ctype.h>
  22 #include <errno.h>
  23 #include <execinfo.h>
  24 #include <fcntl.h>
  25 #include <signal.h>
  26 #include <stdint.h>
  27 #include <stdio.h>
  28 #include <stdlib.h>
  29 #include <string.h>
  30 #include <unistd.h>
  31 #include <_itoa.h>
  32 #include <ldsodefs.h>
  33
  34 /* This file defines macros to access the content of the sigcontext element
  35    passed up by the signal handler.  */
  36 #include <sigcontextinfo.h>
  37
  38 #ifdef SA_SIGINFO
  39 # define SIGCONTEXT siginfo_t *info, void *
  40 #endif
  41
  42 /* Get code to possibly dump the content of all registers.  */
  43 #include <register-dump.h>
  44
  45 /* We'll use this a lot.  */
  46 #define WRITE_STRING(s) write (fd, s, strlen (s))
  47
  48 /* Name of the output file.  */
  49 static const char *fname;
  50
  51
  52 /* We better should not use `strerror' since it can call far too many
  53    other functions which might fail.  Do it here ourselves.  */
  54 static void
  55 write_strsignal (int fd, int signal)
  56 {
  57   if (signal < 0 || signal >= _NSIG || _sys_siglist[signal] == NULL)
  58     {
  59       char buf[30];
  60       char *ptr = _itoa_word (signal, &buf[sizeof (buf)], 10, 0);
  61       WRITE_STRING ("signal ");
  62       write (fd, buf, &buf[sizeof (buf)] - ptr);
  63     }
  64   else
  65     WRITE_STRING (_sys_siglist[signal]);
  66 }
  67
  68
  69 /* This function is called when a segmentation fault is caught.  The system
  70    is in an unstable state now.  This means especially that malloc() might
  71    not work anymore.  */
  72 static void
  73 catch_segfault (int signal, SIGCONTEXT ctx)
  74 {
  75   int fd, cnt, i;
  76   void **arr;
  77   struct sigaction sa;
  78   uintptr_t pc;
  79
  80   /* This is the name of the file we are writing to.  If none is given
  81      or we cannot write to this file write to stderr.  */
  82   fd = 2;
  83   if (fname != NULL)
  84     {
  85       fd = open (fname, O_TRUNC | O_WRONLY | O_CREAT, 0666);
  86       if (fd == -1)
  87         fd = 2;
  88     }
  89
  90   WRITE_STRING ("*** ");
  91   write_strsignal (fd, signal);
  92   WRITE_STRING ("\n");
  93
  94 #ifdef REGISTER_DUMP
  95   REGISTER_DUMP;
  96 #endif
  97
  98   WRITE_STRING ("\nBacktrace:\n");
  99
 100   /* Get the backtrace.  */
 101   arr = alloca (256 * sizeof (void *));
 102   cnt = backtrace (arr, 256);
 103
 104   /* Now try to locate the PC from signal context in the backtrace.
 105      Normally it will be found at arr[2], but it might appear later
 106      if there were some signal handler wrappers.  Allow a few bytes
 107      difference to cope with as many arches as possible.  */
 108   pc = sigcontext_get_pc (ctx);
 109   for (i = 0; i < cnt; ++i)
 110     if ((uintptr_t) arr[i] >= pc - 16 && (uintptr_t) arr[i] <= pc + 16)
 111       break;
 112
 113   /* If we haven't found it, better dump full backtrace even including
 114      the signal handler frames instead of not dumping anything.  */
 115   if (i == cnt)
 116     i = 0;
 117
 118   /* Now generate nicely formatted output.  */
 119   __backtrace_symbols_fd (arr + i, cnt - i, fd);
 120
 121 #ifdef HAVE_PROC_SELF
 122   /* Now the link map.  */
 123   int mapfd = open ("/proc/self/maps", O_RDONLY);
 124   if (mapfd != -1)
 125     {
 126       write (fd, "\nMemory map:\n\n", 14);
 127
 128       char buf[256];
 129       ssize_t n;
 130
 131       while ((n = TEMP_FAILURE_RETRY (read (mapfd, buf, sizeof (buf)))) > 0)
 132         TEMP_FAILURE_RETRY (write (fd, buf, n));
 133
 134       close (mapfd);
 135     }
 136 #endif
 137
 138   /* Pass on the signal (so that a core file is produced).  */
 139   sa.sa_handler = SIG_DFL;
 140   sigemptyset (&sa.sa_mask);
 141   sa.sa_flags = 0;
 142   sigaction (signal, &sa, NULL);
 143   raise (signal);
 144 }
 145
 146
 147 static void
 148 __attribute__ ((constructor))
 149 install_handler (void)
 150 {
 151   struct sigaction sa;
 152   const char *sigs = getenv ("SEGFAULT_SIGNALS");
 153   const char *name;
 154
 155 #ifdef SA_SIGINFO
 156   sa.sa_sigaction = catch_segfault;
 157   sa.sa_flags = SA_SIGINFO;
 158 #else
 159   sa.sa_handler = (void*) catch_segfault;
 160   sa.sa_flags = 0;
 161 #endif
 162   sigemptyset (&sa.sa_mask);
 163   sa.sa_flags |= SA_RESTART;
 164
 165   /* Maybe we are expected to use an alternative stack.  */
 166   if (getenv ("SEGFAULT_USE_ALTSTACK") != 0)
 167     {
 168       void *stack_mem = malloc (2 * SIGSTKSZ);
 169       stack_t ss;
 170
 171       if (stack_mem != NULL)
 172         {
 173           ss.ss_sp = stack_mem;
 174           ss.ss_flags = 0;
 175           ss.ss_size = 2 * SIGSTKSZ;
 176
 177           if (sigaltstack (&ss, NULL) == 0)
 178             sa.sa_flags |= SA_ONSTACK;
 179         }
 180     }
 181
 182   if (sigs == NULL)
 183     sigaction (SIGSEGV, &sa, NULL);
 184   else if (sigs[0] == '\0')
 185     /* Do not do anything.  */
 186     return;
 187   else
 188     {
 189       const char *where;
 190       int all = __strcasecmp (sigs, "all") == 0;
 191
 192 #define INSTALL_FOR_SIG(sig, name) \
 193       where = __strcasestr (sigs, name);                                      \
 194       if (all || (where != NULL                                               \
 195                   && (where == sigs || !isalnum (where[-1]))                  \
 196                   && !isalnum (where[sizeof (name) - 1])))                    \
 197         sigaction (sig, &sa, NULL);
 198
 199       INSTALL_FOR_SIG (SIGSEGV, "segv");
 200       INSTALL_FOR_SIG (SIGILL, "ill");
 201 #ifdef SIGBUS
 202       INSTALL_FOR_SIG (SIGBUS, "bus");
 203 #endif
 204 #ifdef SIGSTKFLT
 205       INSTALL_FOR_SIG (SIGSTKFLT, "stkflt");
 206 #endif
 207       INSTALL_FOR_SIG (SIGABRT, "abrt");
 208       INSTALL_FOR_SIG (SIGFPE, "fpe");
 209     }
 210
 211   /* Preserve the output file name if there is any given.  */
 212   name = getenv ("SEGFAULT_OUTPUT_NAME");
 213   if (name != NULL && name[0] != '\0')
 214     {
 215       int ret = access (name, R_OK | W_OK);
 216
 217       if (ret == 0 || (ret == -1 && errno == ENOENT))
 218         fname = __strdup (name);
 219     }
 220 }