aboutsummaryrefslogtreecommitdiff
path: root/sysdeps/generic/segfault.c
blob: 6504123e1861c5fbcb05e48b86416b57b1238aad (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
/* Catch segmentation faults and print backtrace.
   Copyright (C) 1998 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Ulrich Drepper <drepper@cygnus.com>, 1998.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If not,
   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

#include <execinfo.h>
#include <fcntl.h>
#include <signal.h>
#include <stdlib.h>
#include <unistd.h>

/* This file defines macros to access the content of the sigcontext element
   passed up by the signal handler.  */
#include <sigcontextinfo.h>

/* This is a global variable set at program start time.  It marks the
   highest used stack address.  */
extern void *__libc_stack_end;


/* This implementation assumes a stack layout that matches the defaults
   used by gcc's `__builtin_frame_address' and `__builtin_return_address'
   (FP is the frame pointer register):

	  +-----------------+     +-----------------+
    FP -> | previous FP --------> | previous FP ------>...
	  |                 |     |                 |
	  | return address  |     | return address  |
	  +-----------------+     +-----------------+

  */

/* Get some notion of the current stack.  Need not be exactly the top
   of the stack, just something somewhere in the current frame.  */
#ifndef CURRENT_STACK_FRAME
# define CURRENT_STACK_FRAME  ({ char __csf; &__csf; })
#endif

/* By default we assume that the stack grows downward.  */
#ifndef INNER_THAN
# define INNER_THAN <
#endif

struct layout
{
  struct layout *next;
  void *return_address;
};


/* This function is called when a segmentation fault is caught.  The system
   is in an instable state now.  This means especially that malloc() might
   not work anymore.  */
static void
catch_segfault (int signal, SIGCONTEXT ctx)
{
  struct layout *current;
  void *top_frame;
  void *top_stack;
  const char *fname;
  int fd;
  void **arr;
  size_t cnt;

  /* This is the name of the file we are writing to.  If none is given
     or we cannot write to this file write to stderr.  */
  fd = 2;
  fname = getenv ("SEGFAULT_OUTPUT_NAME");
  if (fname != NULL && fname[0] != '\0')
    {
      fd = open (fname, O_TRUNC | O_WRONLY | O_CREAT);
      if (fd == -1)
	fd = 2;
    }

#define WRITE_STRING(s) write (fd, s, sizeof (s) - 1)
  WRITE_STRING ("*** Segmentation Fault\n");
  WRITE_STRING ("Backtrace:\n");

  top_frame = GET_FRAME (ctx);
  top_stack = GET_STACK (ctx);

  /* First count how many entries we'll have.  */
  cnt = 1;
  current = (struct layout *) top_frame;
  while (!((void *) current INNER_THAN top_stack
	   || !((void *) current INNER_THAN __libc_stack_end)))
    {
      ++cnt;

      current = current->next;
    }

  arr = alloca (cnt * sizeof (void *));

  /* First handle the program counter from the structure.  */
  arr[0] = GET_PC (ctx);

  current = (struct layout *) top_frame;
  cnt = 1;
  while (!((void *) current INNER_THAN top_stack
	   || !((void *) current INNER_THAN __libc_stack_end)))
    {
      arr[cnt++] = current->return_address;

      current = current->next;
    }

  /* Now generate nicely formatted output.  */
  __backtrace_symbols_fd (arr, cnt, fd);

  /* Nothing else to do.  */
  _exit (128 + SIGSEGV);
}


static void
__attribute__ ((constructor))
install_handler (void)
{
  struct sigaction sa;

  sa.sa_handler = (void *) catch_segfault;
  sigemptyset (&sa.sa_mask);
  sa.sa_flags = SA_RESTART;

  sigaction (SIGSEGV, &sa, NULL);

  /* Maybe we are expected to use an alternative stack.  */
  if (getenv ("SEGFAULT_USE_ALTSTACK") != 0)
    {
      void *stack_mem = malloc (2 * SIGSTKSZ);
      struct sigaltstack ss;

      if (stack_mem != NULL)
	{
	  ss.ss_sp = stack_mem;
	  ss.ss_flags = SS_ONSTACK;
	  ss.ss_size = 2 * SIGSTKSZ;

	  sigaltstack (&ss, NULL);
	}
    }
}