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/* Stack overflow handling.
Copyright (C) 2002, 2004, 2006, 2008-2021 Free Software Foundation, Inc.
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program 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 General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>. */
/* Written by Paul Eggert. */
/* NOTES:
A program that uses alloca, dynamic arrays, or large local
variables may extend the stack by more than a page at a time. If
so, when the stack overflows the operating system may not detect
the overflow until the program uses the array, and this module may
incorrectly report a program error instead of a stack overflow.
To avoid this problem, allocate only small objects on the stack; a
program should be OK if it limits single allocations to a page or
less. Allocate larger arrays in static storage, or on the heap
(e.g., with malloc). Yes, this is a pain, but we don't know of any
better solution that is portable.
No attempt has been made to deal with multithreaded applications. */
#include <config.h>
#include "c-stack.h"
#include <errno.h>
#include <inttypes.h>
#include <signal.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#if DEBUG
# include <stdio.h>
#endif
#include <sigsegv.h>
#include "exitfail.h"
#include "getprogname.h"
#include "idx.h"
#include "ignore-value.h"
#include "gettext.h"
#define _(msgid) gettext (msgid)
#if HAVE_STACK_OVERFLOW_RECOVERY
/* Storage for the alternate signal stack.
64 KiB is not too large for Gnulib-using apps, and is large enough
for all known platforms. Smaller sizes may run into trouble.
For example, libsigsegv 2.6 through 2.8 have a bug where some
architectures use more than the Linux default of an 8 KiB alternate
stack when deciding if a fault was caused by stack overflow. */
static max_align_t alternate_signal_stack[(64 * 1024
+ sizeof (max_align_t) - 1)
/ sizeof (max_align_t)];
/* The user-specified action to take when a SEGV-related program error
or stack overflow occurs. */
static _GL_ASYNC_SAFE void (* volatile segv_action) (int);
/* Translated messages for program errors and stack overflow. Do not
translate them in the signal handler, since gettext is not
async-signal-safe. */
static char const * volatile program_error_message;
static char const * volatile stack_overflow_message;
/* Output an error message, then exit with status EXIT_FAILURE if it
appears to have been a stack overflow, or with a core dump
otherwise. This function is async-signal-safe. */
static char const * volatile progname;
static _GL_ASYNC_SAFE _Noreturn void
die (int signo)
{
segv_action (signo);
char const *message = signo ? program_error_message : stack_overflow_message;
/* If the message is short, write it all at once to avoid
interleaving with other messages. Avoid writev as it is not
documented to be async-signal-safe. */
size_t prognamelen = strlen (progname);
size_t messagelen = strlen (message);
static char const separator[] = {':', ' '};
char buf[sizeof alternate_signal_stack / 16 + sizeof separator];
idx_t buflen;
if (prognamelen + messagelen < sizeof buf - sizeof separator)
{
char *p = mempcpy (buf, progname, prognamelen);
p = mempcpy (p, separator, sizeof separator);
p = mempcpy (p, message, messagelen);
*p++ = '\n';
buflen = p - buf;
}
else
{
ignore_value (write (STDERR_FILENO, progname, prognamelen));
ignore_value (write (STDERR_FILENO, separator, sizeof separator));
ignore_value (write (STDERR_FILENO, message, messagelen));
buf[0] = '\n';
buflen = 1;
}
ignore_value (write (STDERR_FILENO, buf, buflen));
if (! signo)
_exit (exit_failure);
raise (signo);
abort ();
}
static _GL_ASYNC_SAFE void
null_action (int signo _GL_UNUSED)
{
}
/* Pacify GCC 9.3.1, which otherwise would complain about segv_handler. */
# if 4 < __GNUC__ + (6 <= __GNUC_MINOR__)
# pragma GCC diagnostic ignored "-Wsuggest-attribute=pure"
# endif
/* Nonzero if general segv handler could not be installed. */
static volatile int segv_handler_missing;
/* Handle a segmentation violation and exit if it cannot be stack
overflow. This function is async-signal-safe. */
static _GL_ASYNC_SAFE int
segv_handler (void *address _GL_UNUSED, int serious)
{
# if DEBUG
{
char buf[1024];
int saved_errno = errno;
ignore_value (write (STDERR_FILENO, buf,
sprintf (buf, "segv_handler serious=%d\n", serious)));
errno = saved_errno;
}
# endif
/* If this fault is not serious, return 0 to let the stack overflow
handler take a shot at it. */
if (!serious)
return 0;
die (SIGSEGV);
}
/* Handle a segmentation violation that is likely to be a stack
overflow and exit. This function is async-signal-safe. */
static _GL_ASYNC_SAFE _Noreturn void
overflow_handler (int emergency, stackoverflow_context_t context _GL_UNUSED)
{
# if DEBUG
{
char buf[1024];
ignore_value (write (STDERR_FILENO, buf,
sprintf (buf, ("overflow_handler emergency=%d"
" segv_handler_missing=%d\n"),
emergency, segv_handler_missing)));
}
# endif
die ((!emergency || segv_handler_missing) ? 0 : SIGSEGV);
}
int
c_stack_action (_GL_ASYNC_SAFE void (*action) (int))
{
segv_action = action ? action : null_action;
program_error_message = _("program error");
stack_overflow_message = _("stack overflow");
progname = getprogname ();
/* Always install the overflow handler. */
if (stackoverflow_install_handler (overflow_handler,
alternate_signal_stack,
sizeof alternate_signal_stack))
{
errno = ENOTSUP;
return -1;
}
/* Try installing a general handler; if it fails, then treat all
segv as stack overflow. */
segv_handler_missing = sigsegv_install_handler (segv_handler);
return 0;
}
#else /* !HAVE_STACK_OVERFLOW_RECOVERY */
int
c_stack_action (_GL_ASYNC_SAFE void (*action) (int) _GL_UNUSED)
{
errno = ENOTSUP;
return -1;
}
#endif
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