1/*	$NetBSD$	*/
2
3/* Stack overflow handling.
4
5   Copyright (C) 2002 Free Software Foundation, Inc.
6
7   This program is free software; you can redistribute it and/or modify
8   it under the terms of the GNU General Public License as published by
9   the Free Software Foundation; either version 2, or (at your option)
10   any later version.
11
12   This program 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
15   GNU 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, write to the Free Software Foundation,
19   Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
20
21/* Written by Paul Eggert.  */
22
23/* This module assumes that each stack frame is smaller than a page.
24   If you use alloca, dynamic arrays, or large local variables, your
25   program may extend the stack by more than a page at a time.  If so,
26   the code below may incorrectly report a program error, or worse
27   yet, may not detect the overflow at all.  To avoid this problem,
28   don't use large local arrays.  */
29
30#if HAVE_CONFIG_H
31# include <config.h>
32#endif
33
34#include "gettext.h"
35#define _(msgid) gettext (msgid)
36
37#include <errno.h>
38#ifndef ENOTSUP
39# define ENOTSUP EINVAL
40#endif
41
42#if HAVE_INTTYPES_H
43# include <inttypes.h>
44#else
45# if HAVE_STDINT_H
46#  include <stdint.h>
47# endif
48#endif
49
50#include <signal.h>
51#include <stdlib.h>
52#include <string.h>
53
54#if HAVE_UNISTD_H
55# include <unistd.h>
56#endif
57#ifndef STDERR_FILENO
58# define STDERR_FILENO 2
59#endif
60
61#include "c-stack.h"
62#include "exitfail.h"
63
64extern char *program_name;
65
66#if HAVE_XSI_STACK_OVERFLOW_HEURISTIC
67
68# include <ucontext.h>
69
70
71/* Storage for the alternate signal stack.  */
72static union
73{
74  char buffer[SIGSTKSZ];
75
76  /* These other members are for proper alignment.  There's no
77     standard way to guarantee stack alignment, but this seems enough
78     in practice.  */
79  long double ld;
80  uintmax_t u;
81  void *p;
82} alternate_signal_stack;
83
84
85/* Direction of the C runtime stack.  This function is
86   async-signal-safe.  */
87
88# if STACK_DIRECTION
89#  define find_stack_direction(ptr) STACK_DIRECTION
90# else
91static int
92find_stack_direction (char const *addr)
93{
94  char dummy;
95  return ! addr ? find_stack_direction (&dummy) : addr < &dummy ? 1 : -1;
96}
97# endif
98
99/* The SIGSEGV handler.  */
100static void (* volatile segv_action) (int, siginfo_t *, void *);
101
102/* Handle a segmentation violation and exit.  This function is
103   async-signal-safe.  */
104
105static void
106segv_handler (int signo, siginfo_t *info, void *context)
107{
108  /* Clear SIGNO if it seems to have been a stack overflow.  */
109  if (0 < info->si_code)
110    {
111      /* If the faulting address is within the stack, or within one
112	 page of the stack end, assume that it is a stack
113	 overflow.  */
114      ucontext_t const *user_context = context;
115      char const *stack_min = user_context->uc_stack.ss_sp;
116      size_t stack_size = user_context->uc_stack.ss_size;
117      char const *faulting_address = info->si_addr;
118      size_t s = faulting_address - stack_min;
119      size_t page_size = sysconf (_SC_PAGESIZE);
120      if (find_stack_direction (0) < 0)
121	s += page_size;
122      if (s < stack_size + page_size)
123	signo = 0;
124    }
125
126  segv_action (signo, info, context);
127}
128
129#endif /* HAVE_XSI_STACK_OVERFLOW_HEURISTIC */
130
131
132/* Translated messages for program errors and stack overflow.  Do not
133   translate them in the signal handler, since gettext is not
134   async-signal-safe.  */
135static char const * volatile program_error_message;
136static char const * volatile stack_overflow_message;
137
138/* Output an error message, then exit with status EXIT_FAILURE if it
139   appears to have been a stack overflow, or with a core dump
140   otherwise.  This function is async-signal-safe.  */
141
142void
143c_stack_die (int signo, siginfo_t *info, void *context)
144{
145  char const *message =
146    signo ? program_error_message : stack_overflow_message;
147  write (STDERR_FILENO, program_name, strlen (program_name));
148  write (STDERR_FILENO, ": ", 2);
149  write (STDERR_FILENO, message, strlen (message));
150  write (STDERR_FILENO, "\n", 1);
151  if (! signo)
152    _exit (exit_failure);
153#if HAVE_SIGINFO_T
154  if (context && info && 0 <= info->si_code)
155    {
156      /* Re-raise the exception at the same address.  */
157      char *addr = info->si_addr;
158      *addr = 0;
159    }
160#endif
161  kill (getpid (), signo);
162}
163
164
165/* Set up ACTION so that it is invoked on C stack overflow.  Return -1
166   (setting errno) if this cannot be done.
167
168   ACTION must invoke only async-signal-safe functions.  ACTION
169   together with its callees must not require more than SIGSTKSZ bytes
170   of stack space.  */
171
172int
173c_stack_action (void (*action) (int, siginfo_t *, void *))
174{
175#if ! HAVE_XSI_STACK_OVERFLOW_HEURISTIC
176  errno = ENOTSUP;
177  return -1;
178#else
179  struct sigaction act;
180  stack_t st;
181  int r;
182
183  st.ss_flags = 0;
184  st.ss_sp = alternate_signal_stack.buffer;
185  st.ss_size = sizeof alternate_signal_stack.buffer;
186  r = sigaltstack (&st, 0);
187  if (r != 0)
188    return r;
189
190  program_error_message = _("program error");
191  stack_overflow_message = _("stack overflow");
192  segv_action = action;
193
194  sigemptyset (&act.sa_mask);
195
196  /* POSIX 1003.1-2001 says SA_RESETHAND implies SA_NODEFER, but this
197     is not true on Solaris 8 at least.  It doesn't hurt to use
198     SA_NODEFER here, so leave it in.  */
199  act.sa_flags = SA_NODEFER | SA_ONSTACK | SA_RESETHAND | SA_SIGINFO;
200
201  act.sa_sigaction = segv_handler;
202  return sigaction (SIGSEGV, &act, 0);
203#endif
204}
205
206#if DEBUG
207
208#include <stdio.h>
209
210int volatile exit_failure;
211
212static long
213recurse (char *p)
214{
215  char array[500];
216  array[0] = 1;
217  return *p + recurse (array);
218}
219
220char *program_name;
221
222int
223main (int argc, char **argv)
224{
225  program_name = argv[0];
226  c_stack_action (c_stack_die);
227  return recurse ("\1");
228}
229
230#endif /* DEBUG */
231
232/*
233Local Variables:
234compile-command: "gcc -D_GNU_SOURCE -DDEBUG \
235  -DHAVE_INTTYPES_H -DHAVE_SIGINFO_T \
236  -DHAVE_XSI_STACK_OVERFLOW_HEURISTIC -DHAVE_UNISTD_H \
237  -Wall -W -g c-stack.c -o c-stack"
238End:
239*/
240