1: /* Catch segmentation faults and print backtrace.
    2:    Copyright (C) 1998, 1999, 2000, 2001, 2002, 2004, 2007
    3:    Free Software Foundation, Inc.
    4:    This file is part of the GNU C Library.
    5:    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1998.
    6: 
    7:    The GNU C Library is free software; you can redistribute it and/or
    8:    modify it under the terms of the GNU Lesser General Public
    9:    License as published by the Free Software Foundation; either
   10:    version 2.1 of the License, or (at your option) any later version.
   11: 
   12:    The GNU C Library is distributed in the hope that it will be useful,
   13:    but WITHOUT ANY WARRANTY; without even the implied warranty of
   14:    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   15:    Lesser General Public License for more details.
   16: 
   17:    You should have received a copy of the GNU Lesser General Public
   18:    License along with the GNU C Library; if not, write to the Free
   19:    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   20:    02111-1307 USA.  */
   21: 
   22: #include <alloca.h>
   23: #include <ctype.h>
   24: #include <errno.h>
   25: #include <execinfo.h>
   26: #include <fcntl.h>
   27: #include <signal.h>
   28: #include <stdint.h>
   29: #include <stdio.h>
   30: #include <stdlib.h>
   31: #include <string.h>
   32: #include <unistd.h>
   33: #include <stdio-common/_itoa.h>
   34: #include <ldsodefs.h>
   35: 
   36: #include <bp-checks.h>
   37: 
   38: /* This file defines macros to access the content of the sigcontext element
   39:    passed up by the signal handler.  */
   40: #include <sigcontextinfo.h>
   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 = (uintptr_t) 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:   sa.sa_handler = (void *) catch_segfault;
  156:   sigemptyset (&sa.sa_mask);
  157:   sa.sa_flags = SA_RESTART;
  158: 
  159:   /* Maybe we are expected to use an alternative stack.  */
  160:   if (getenv ("SEGFAULT_USE_ALTSTACK") != 0)
  161:     {
  162:       void *stack_mem = malloc (2 * SIGSTKSZ);
  163:       struct sigaltstack ss;
  164: 
  165:       if (stack_mem != NULL)
  166:         {
  167:           ss.ss_sp = stack_mem;
  168:           ss.ss_flags = 0;
  169:           ss.ss_size = 2 * SIGSTKSZ;
  170: 
  171:           if (sigaltstack (&ss, NULL) == 0)
  172:             sa.sa_flags |= SA_ONSTACK;
  173:         }
  174:     }
  175: 
  176:   if (sigs == NULL)
  177:     sigaction (SIGSEGV, &sa, NULL);
  178:   else if (sigs[0] == '\0')
  179:     /* Do not do anything.  */
  180:     return;
  181:   else
  182:     {
  183:       const char *where;
  184:       int all = __strcasecmp (sigs, "all") == 0;
  185: 
  186: #define INSTALL_FOR_SIG(sig, name) \
  187:       where = __strcasestr (sigs, name);                                      \
  188:       if (all || (where != NULL                                               \
  189:                   && (where == sigs || !isalnum (where[-1]))                \
  190:                   && !isalnum (where[sizeof (name) - 1])))                  \
  191:         sigaction (sig, &sa, NULL);
  192: 
  193:       INSTALL_FOR_SIG (SIGSEGV, "segv");
  194:       INSTALL_FOR_SIG (SIGILL, "ill");
  195: #ifdef SIGBUS
  196:       INSTALL_FOR_SIG (SIGBUS, "bus");
  197: #endif
  198: #ifdef SIGSTKFLT
  199:       INSTALL_FOR_SIG (SIGSTKFLT, "stkflt");
  200: #endif
  201:       INSTALL_FOR_SIG (SIGABRT, "abrt");
  202:       INSTALL_FOR_SIG (SIGFPE, "fpe");
  203:     }
  204: 
  205:   /* Preserve the output file name if there is any given.  */
  206:   name = getenv ("SEGFAULT_OUTPUT_NAME");
  207:   if (name != NULL && name[0] != '\0')
  208:     {
  209:       int ret = access (name, R_OK | W_OK);
  210: 
  211:       if (ret == 0 || (ret == -1 && errno == ENOENT))
  212:         fname = __strdup (name);
  213:     }
  214: }