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/* Stack overflow handling.
Copyright (C) 2002, 2004, 2006, 2008-2016 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 <http://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>
#ifndef __attribute__
# if __GNUC__ < 3
# define __attribute__(x)
# endif
#endif
#include "gettext.h"
#define _(msgid) gettext (msgid)
#include <errno.h>
#include <signal.h>
#if ! HAVE_STACK_T && ! defined stack_t
typedef struct sigaltstack stack_t;
#endif
#ifndef SIGSTKSZ
# define SIGSTKSZ 16384
#elif HAVE_LIBSIGSEGV && SIGSTKSZ < 16384
/* libsigsegv 2.6 through 2.8 have a bug where some architectures use
more than the Linux default of an 8k alternate stack when deciding
if a fault was caused by stack overflow. */
# undef SIGSTKSZ
# define SIGSTKSZ 16384
#endif
#include <stdlib.h>
#include <string.h>
/* Posix 2001 declares ucontext_t in <ucontext.h>, Posix 200x in
<signal.h>. */
#if HAVE_UCONTEXT_H
# include <ucontext.h>
#endif
#include <unistd.h>
#if HAVE_LIBSIGSEGV
# error #include <sigsegv.h>
#endif
#include "c-stack.h"
#include "exitfail.h"
#include "ignore-value.h"
#include "getprogname.h"
#if defined SA_ONSTACK && defined SA_SIGINFO
# define SIGINFO_WORKS 1
#else
# define SIGINFO_WORKS 0
# ifndef SA_ONSTACK
# define SA_ONSTACK 0
# endif
#endif
/* The user-specified action to take when a SEGV-related program error
or stack overflow occurs. */
static 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 _Noreturn void
die (int signo)
{
char const *message;
#if !SIGINFO_WORKS && !HAVE_LIBSIGSEGV
/* We can't easily determine whether it is a stack overflow; so
assume that the rest of our program is perfect (!) and that
this segmentation violation is a stack overflow. */
signo = 0;
#endif /* !SIGINFO_WORKS && !HAVE_LIBSIGSEGV */
segv_action (signo);
message = signo ? program_error_message : stack_overflow_message;
ignore_value (write (STDERR_FILENO, getprogname (), strlen (getprogname ())));
ignore_value (write (STDERR_FILENO, ": ", 2));
ignore_value (write (STDERR_FILENO, message, strlen (message)));
ignore_value (write (STDERR_FILENO, "\n", 1));
if (! signo)
_exit (exit_failure);
raise (signo);
abort ();
}
#if (HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK \
&& HAVE_STACK_OVERFLOW_HANDLING) || HAVE_LIBSIGSEGV
/* Storage for the alternate signal stack. */
static union
{
char buffer[SIGSTKSZ];
/* These other members are for proper alignment. There's no
standard way to guarantee stack alignment, but this seems enough
in practice. */
long double ld;
long l;
void *p;
} alternate_signal_stack;
static void
null_action (int signo __attribute__ ((unused)))
{
}
#endif /* SIGALTSTACK || LIBSIGSEGV */
/* Only use libsigsegv if we need it; platforms like Solaris can
detect stack overflow without the overhead of an external
library. */
#if HAVE_LIBSIGSEGV && ! HAVE_XSI_STACK_OVERFLOW_HEURISTIC
/* 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 int segv_handler (void *address __attribute__ ((unused)),
int serious)
{
# if DEBUG
{
char buf[1024];
sprintf (buf, "segv_handler serious=%d\n", serious);
write (STDERR_FILENO, buf, strlen (buf));
}
# 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 _Noreturn void
overflow_handler (int emergency,
stackoverflow_context_t context __attribute__ ((unused)))
{
# if DEBUG
{
char buf[1024];
sprintf (buf, "overflow_handler emergency=%d segv_handler_missing=%d\n",
emergency, segv_handler_missing);
write (STDERR_FILENO, buf, strlen (buf));
}
# endif
die ((!emergency || segv_handler_missing) ? 0 : SIGSEGV);
}
int
c_stack_action (void (*action) (int))
{
segv_action = action ? action : null_action;
program_error_message = _("program error");
stack_overflow_message = _("stack overflow");
/* Always install the overflow handler. */
if (stackoverflow_install_handler (overflow_handler,
alternate_signal_stack.buffer,
sizeof alternate_signal_stack.buffer))
{
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;
}
#elif HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK && HAVE_STACK_OVERFLOW_HANDLING
# if SIGINFO_WORKS
/* Handle a segmentation violation and exit. This function is
async-signal-safe. */
static _Noreturn void
segv_handler (int signo, siginfo_t *info,
void *context __attribute__ ((unused)))
{
/* Clear SIGNO if it seems to have been a stack overflow. */
# if ! HAVE_XSI_STACK_OVERFLOW_HEURISTIC
/* We can't easily determine whether it is a stack overflow; so
assume that the rest of our program is perfect (!) and that
this segmentation violation is a stack overflow.
Note that although both Linux and Solaris provide
sigaltstack, SA_ONSTACK, and SA_SIGINFO, currently only
Solaris satisfies the XSI heuristic. This is because
Solaris populates uc_stack with the details of the
interrupted stack, while Linux populates it with the details
of the current stack. */
signo = 0;
# else
if (0 < info->si_code)
{
/* If the faulting address is within the stack, or within one
page of the stack, assume that it is a stack overflow. */
ucontext_t const *user_context = context;
char const *stack_base = user_context->uc_stack.ss_sp;
size_t stack_size = user_context->uc_stack.ss_size;
char const *faulting_address = info->si_addr;
size_t page_size = sysconf (_SC_PAGESIZE);
size_t s = faulting_address - stack_base + page_size;
if (s < stack_size + 2 * page_size)
signo = 0;
# if DEBUG
{
char buf[1024];
sprintf (buf,
"segv_handler fault=%p base=%p size=%lx page=%lx signo=%d\n",
faulting_address, stack_base, (unsigned long) stack_size,
(unsigned long) page_size, signo);
write (STDERR_FILENO, buf, strlen (buf));
}
# endif
}
# endif
die (signo);
}
# endif
int
c_stack_action (void (*action) (int))
{
int r;
stack_t st;
struct sigaction act;
st.ss_flags = 0;
# if SIGALTSTACK_SS_REVERSED
/* Irix mistakenly treats ss_sp as the upper bound, rather than
lower bound, of the alternate stack. */
st.ss_sp = alternate_signal_stack.buffer + SIGSTKSZ - sizeof (void *);
st.ss_size = sizeof alternate_signal_stack.buffer - sizeof (void *);
# else
st.ss_sp = alternate_signal_stack.buffer;
st.ss_size = sizeof alternate_signal_stack.buffer;
# endif
r = sigaltstack (&st, NULL);
if (r != 0)
return r;
segv_action = action ? action : null_action;
program_error_message = _("program error");
stack_overflow_message = _("stack overflow");
sigemptyset (&act.sa_mask);
# if SIGINFO_WORKS
/* POSIX 1003.1-2001 says SA_RESETHAND implies SA_NODEFER, but
this is not true on Solaris 8 at least. It doesn't hurt to use
SA_NODEFER here, so leave it in. */
act.sa_flags = SA_NODEFER | SA_ONSTACK | SA_RESETHAND | SA_SIGINFO;
act.sa_sigaction = segv_handler;
# else
act.sa_flags = SA_NODEFER | SA_ONSTACK | SA_RESETHAND;
act.sa_handler = die;
# endif
# if FAULT_YIELDS_SIGBUS
if (sigaction (SIGBUS, &act, NULL) < 0)
return -1;
# endif
return sigaction (SIGSEGV, &act, NULL);
}
#else /* ! ((HAVE_SIGALTSTACK && HAVE_DECL_SIGALTSTACK
&& HAVE_STACK_OVERFLOW_HANDLING) || HAVE_LIBSIGSEGV) */
int
c_stack_action (void (*action) (int) __attribute__ ((unused)))
{
errno = ENOTSUP;
return -1;
}
#endif
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