sysdeps/generic/segfault.c

   1 /* Catch segmentation faults and print backtrace.
   2    Copyright (C) 1998 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 Library General Public License as
   8    published by the Free Software Foundation; either version 2 of the
   9    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    Library General Public License for more details.
  15
  16    You should have received a copy of the GNU Library General Public
  17    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  18    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  19    Boston, MA 02111-1307, USA.  */
  20
  21 #include <execinfo.h>
  22 #include <fcntl.h>
  23 #include <signal.h>
  24 #include <stdlib.h>
  25 #include <unistd.h>
  26
  27 /* This file defines macros to access the content of the sigcontext element
  28    passed up by the signal handler.  */
  29 #include <sigcontextinfo.h>
  30
  31 /* This is a global variable set at program start time.  It marks the
  32    highest used stack address.  */
  33 extern void *__libc_stack_end;
  34
  35
  36 /* This implementation assumes a stack layout that matches the defaults
  37    used by gcc's `__builtin_frame_address' and `__builtin_return_address'
  38    (FP is the frame pointer register):
  39
  40           +-----------------+     +-----------------+
  41     FP -> | previous FP --------> | previous FP ------>...
  42           |                 |     |                 |
  43           | return address  |     | return address  |
  44           +-----------------+     +-----------------+
  45
  46   */
  47
  48 /* Get some notion of the current stack.  Need not be exactly the top
  49    of the stack, just something somewhere in the current frame.  */
  50 #ifndef CURRENT_STACK_FRAME
  51 # define CURRENT_STACK_FRAME  ({ char __csf; &__csf; })
  52 #endif
  53
  54 /* By default we assume that the stack grows downward.  */
  55 #ifndef INNER_THAN
  56 # define INNER_THAN <
  57 #endif
  58
  59 struct layout
  60 {
  61   struct layout *next;
  62   void *return_address;
  63 };
  64
  65
  66 /* This function is called when a segmentation fault is caught.  The system
  67    is in an instable state now.  This means especially that malloc() might
  68    not work anymore.  */
  69 static void
  70 catch_segfault (int signal, SIGCONTEXT ctx)
  71 {
  72   struct layout *current;
  73   void *top_frame;
  74   void *top_stack;
  75   const char *fname;
  76   int fd;
  77   void **arr;
  78   size_t cnt;
  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   fname = getenv ("SEGFAULT_OUTPUT_NAME");
  84   if (fname != NULL && fname[0] != '\0')
  85     {
  86       fd = open (fname, O_TRUNC | O_WRONLY | O_CREAT);
  87       if (fd == -1)
  88         fd = 2;
  89     }
  90
  91 #define WRITE_STRING(s) write (fd, s, sizeof (s) - 1)
  92   WRITE_STRING ("*** Segmentation Fault\n");
  93   WRITE_STRING ("Backtrace:\n");
  94
  95   top_frame = GET_FRAME (ctx);
  96   top_stack = GET_STACK (ctx);
  97
  98   /* First count how many entries we'll have.  */
  99   cnt = 1;
 100   current = (struct layout *) top_frame;
 101   while (!((void *) current INNER_THAN top_stack
 102            || !((void *) current INNER_THAN __libc_stack_end)))
 103     {
 104       ++cnt;
 105
 106       current = current->next;
 107     }
 108
 109   arr = alloca (cnt * sizeof (void *));
 110
 111   /* First handle the program counter from the structure.  */
 112   arr[0] = GET_PC (ctx);
 113
 114   current = (struct layout *) top_frame;
 115   cnt = 1;
 116   while (!((void *) current INNER_THAN top_stack
 117            || !((void *) current INNER_THAN __libc_stack_end)))
 118     {
 119       arr[cnt++] = current->return_address;
 120
 121       current = current->next;
 122     }
 123
 124   /* Now generate nicely formatted output.  */
 125   __backtrace_symbols_fd (arr, cnt, fd);
 126
 127   /* Nothing else to do.  */
 128   _exit (128 + SIGSEGV);
 129 }
 130
 131
 132 static void
 133 __attribute__ ((constructor))
 134 install_handler (void)
 135 {
 136   struct sigaction sa;
 137
 138   sa.sa_handler = (void *) catch_segfault;
 139   sigemptyset (&sa.sa_mask);
 140   sa.sa_flags = SA_RESTART;
 141
 142   sigaction (SIGSEGV, &sa, NULL);
 143
 144   /* Maybe we are expected to use an alternative stack.  */
 145   if (getenv ("SEGFAULT_USE_ALTSTACK") != 0)
 146     {
 147       void *stack_mem = malloc (2 * SIGSTKSZ);
 148       struct sigaltstack ss;
 149
 150       if (stack_mem != NULL)
 151         {
 152           ss.ss_sp = stack_mem;
 153           ss.ss_flags = SS_ONSTACK;
 154           ss.ss_size = 2 * SIGSTKSZ;
 155
 156           sigaltstack (&ss, NULL);
 157         }
 158     }
 159 }