1 /* Stack overflow handling.
3 Copyright (C) 2002, 2004, 2006, 2008 Free Software Foundation, Inc.
5 This program is free software: you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation; either version 3 of the License, or
8 (at your option) any later version.
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>. */
18 /* Written by Paul Eggert. */
22 A program that uses alloca, dynamic arrays, or large local
23 variables may extend the stack by more than a page at a time. If
24 so, when the stack overflows the operating system may not detect
25 the overflow until the program uses the array, and this module may
26 incorrectly report a program error instead of a stack overflow.
28 To avoid this problem, allocate only small objects on the stack; a
29 program should be OK if it limits single allocations to a page or
30 less. Allocate larger arrays in static storage, or on the heap
31 (e.g., with malloc). Yes, this is a pain, but we don't know of any
32 better solution that is portable.
34 No attempt has been made to deal with multithreaded applications. */
40 # define __attribute__(x)
45 #define _(msgid) gettext (msgid)
49 # define ENOTSUP EINVAL
53 #if ! HAVE_STACK_T && ! defined stack_t
54 typedef struct sigaltstack stack_t;
57 # define SIGSTKSZ 16384
63 /* Posix 2001 declares ucontext_t in <ucontext.h>, Posix 200x in
66 # include <ucontext.h>
71 # define STDERR_FILENO 2
81 #if defined SA_ONSTACK && defined SA_SIGINFO
82 # define SIGACTION_WORKS 1
84 # define SIGACTION_WORKS 0
90 extern char *program_name;
92 /* The user-specified action to take when a SEGV-related program error
93 or stack overflow occurs. */
94 static void (* volatile segv_action) (int);
96 /* Translated messages for program errors and stack overflow. Do not
97 translate them in the signal handler, since gettext is not
99 static char const * volatile program_error_message;
100 static char const * volatile stack_overflow_message;
102 /* Output an error message, then exit with status EXIT_FAILURE if it
103 appears to have been a stack overflow, or with a core dump
104 otherwise. This function is async-signal-safe. */
106 static void die (int) __attribute__ ((noreturn));
112 message = signo ? program_error_message : stack_overflow_message;
113 write (STDERR_FILENO, program_name, strlen (program_name));
114 write (STDERR_FILENO, ": ", 2);
115 write (STDERR_FILENO, message, strlen (message));
116 write (STDERR_FILENO, "\n", 1);
118 _exit (exit_failure);
123 #if (HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK \
124 && HAVE_STACK_OVERFLOW_HANDLING) || HAVE_LIBSIGSEGV
126 /* Storage for the alternate signal stack. */
129 char buffer[SIGSTKSZ];
131 /* These other members are for proper alignment. There's no
132 standard way to guarantee stack alignment, but this seems enough
137 } alternate_signal_stack;
140 null_action (int signo __attribute__ ((unused)))
144 #endif /* SIGALTSTACK || LIBSIGSEGV */
146 /* Only use libsigsegv if we need it; platforms like Solaris can
147 detect stack overflow without the overhead of an external
149 #if HAVE_LIBSIGSEGV && ! HAVE_XSI_STACK_OVERFLOW_HEURISTIC
151 /* Nonzero if general segv handler could not be installed. */
152 static volatile int segv_handler_missing;
154 /* Handle a segmentation violation and exit if it cannot be stack
155 overflow. This function is async-signal-safe. */
157 static int segv_handler (void *address __attribute__ ((unused)),
163 sprintf (buf, "segv_handler serious=%d\n", serious);
164 write (STDERR_FILENO, buf, strlen (buf));
168 /* If this fault is not serious, return 0 to let the stack overflow
169 handler take a shot at it. */
175 /* Handle a segmentation violation that is likely to be a stack
176 overflow and exit. This function is async-signal-safe. */
178 static void overflow_handler (int, stackoverflow_context_t)
179 __attribute__ ((noreturn));
181 overflow_handler (int emergency,
182 stackoverflow_context_t context __attribute__ ((unused)))
187 sprintf (buf, "overflow_handler emergency=%d segv_handler_missing=%d\n",
188 emergency, segv_handler_missing);
189 write (STDERR_FILENO, buf, strlen (buf));
193 die ((!emergency || segv_handler_missing) ? 0 : SIGSEGV);
197 c_stack_action (void (*action) (int))
199 segv_action = action ? action : null_action;
200 program_error_message = _("program error");
201 stack_overflow_message = _("stack overflow");
203 /* Always install the overflow handler. */
204 if (stackoverflow_install_handler (overflow_handler,
205 alternate_signal_stack.buffer,
206 sizeof alternate_signal_stack.buffer))
211 /* Try installing a general handler; if it fails, then treat all
212 segv as stack overflow. */
213 segv_handler_missing = sigsegv_install_handler (segv_handler);
217 #elif HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK && HAVE_STACK_OVERFLOW_HANDLING
219 /* Direction of the C runtime stack. This function is
220 async-signal-safe. */
223 # define find_stack_direction(ptr) STACK_DIRECTION
226 find_stack_direction (char const *addr)
229 return ! addr ? find_stack_direction (&dummy) : addr < &dummy ? 1 : -1;
235 /* Handle a segmentation violation and exit. This function is
236 async-signal-safe. */
238 static void segv_handler (int, siginfo_t *, void *) __attribute__((noreturn));
240 segv_handler (int signo, siginfo_t *info,
241 void *context __attribute__ ((unused)))
243 /* Clear SIGNO if it seems to have been a stack overflow. */
244 if (0 < info->si_code)
246 # if ! HAVE_XSI_STACK_OVERFLOW_HEURISTIC
247 /* We can't easily determine whether it is a stack overflow; so
248 assume that the rest of our program is perfect (!) and that
249 this segmentation violation is a stack overflow.
251 Note that although both Linux and Solaris provide
252 sigaltstack, SA_ONSTACK, and SA_SIGINFO, currently only
253 Solaris satisfies the XSI heueristic. This is because
254 Solaris populates uc_stack with the details of the
255 interrupted stack, while Linux populates it with the details
256 of the current stack. */
259 /* If the faulting address is within the stack, or within one
260 page of the stack end, assume that it is a stack
262 ucontext_t const *user_context = context;
263 char const *stack_base = user_context->uc_stack.ss_sp;
264 size_t stack_size = user_context->uc_stack.ss_size;
265 char const *faulting_address = info->si_addr;
266 size_t s = faulting_address - stack_base;
267 size_t page_size = sysconf (_SC_PAGESIZE);
268 if (find_stack_direction (NULL) < 0)
270 if (s < stack_size + page_size)
277 "segv_handler fault=%p base=%p size=%lx page=%lx signo=%d\n",
278 faulting_address, stack_base, (unsigned long) stack_size,
279 (unsigned long) page_size, signo);
280 write (STDERR_FILENO, buf, strlen (buf));
291 c_stack_action (void (*action) (int))
295 struct sigaction act;
297 # if SIGALTSTACK_SS_REVERSED
298 /* Irix mistakenly treats ss_sp as the upper bound, rather than
299 lower bound, of the alternate stack. */
300 st.ss_sp = alternate_signal_stack.buffer + SIGSTKSZ - sizeof (void *);
301 st.ss_size = sizeof alternate_signal_stack.buffer - sizeof (void *);
303 st.ss_sp = alternate_signal_stack.buffer;
304 st.ss_size = sizeof alternate_signal_stack.buffer;
306 r = sigaltstack (&st, NULL);
310 segv_action = action ? action : null_action;
311 program_error_message = _("program error");
312 stack_overflow_message = _("stack overflow");
314 sigemptyset (&act.sa_mask);
317 /* POSIX 1003.1-2001 says SA_RESETHAND implies SA_NODEFER, but
318 this is not true on Solaris 8 at least. It doesn't hurt to use
319 SA_NODEFER here, so leave it in. */
320 act.sa_flags = SA_NODEFER | SA_ONSTACK | SA_RESETHAND | SA_SIGINFO;
321 act.sa_sigaction = segv_handler;
323 act.sa_flags = SA_NODEFER | SA_ONSTACK | SA_RESETHAND;
324 act.sa_handler = die;
327 # if FAULT_YIELDS_SIGBUS
328 if (sigaction (SIGBUS, &act, NULL) < 0)
331 return sigaction (SIGSEGV, &act, NULL);
334 #else /* ! ((HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK
335 && HAVE_STACK_OVERFLOW_HANDLING) || HAVE_LIBSIGSEGV) */
338 c_stack_action (void (*action) (int) __attribute__ ((unused)))