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/* Catch segmentation faults and print backtrace.
Copyright (C) 1998-2017 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 Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 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
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#include <alloca.h>
#include <ctype.h>
#include <errno.h>
#include <execinfo.h>
#include <fcntl.h>
#include <signal.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <_itoa.h>
#include <ldsodefs.h>
/* This file defines macros to access the content of the sigcontext element
passed up by the signal handler. */
#include <sigcontextinfo.h>
/* Get code to possibly dump the content of all registers. */
#include <register-dump.h>
/* We'll use this a lot. */
#define WRITE_STRING(s) write (fd, s, strlen (s))
/* Name of the output file. */
static const char *fname;
/* We better should not use `strerror' since it can call far too many
other functions which might fail. Do it here ourselves. */
static void
write_strsignal (int fd, int signal)
{
if (signal < 0 || signal >= _NSIG || _sys_siglist[signal] == NULL)
{
char buf[30];
char *ptr = _itoa_word (signal, &buf[sizeof (buf)], 10, 0);
WRITE_STRING ("signal ");
write (fd, buf, &buf[sizeof (buf)] - ptr);
}
else
WRITE_STRING (_sys_siglist[signal]);
}
/* This function is called when a segmentation fault is caught. The system
is in an unstable state now. This means especially that malloc() might
not work anymore. */
static void
catch_segfault (int signal, SIGCONTEXT ctx)
{
int fd, cnt, i;
void **arr;
struct sigaction sa;
uintptr_t pc;
/* 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;
if (fname != NULL)
{
fd = open (fname, O_TRUNC | O_WRONLY | O_CREAT, 0666);
if (fd == -1)
fd = 2;
}
WRITE_STRING ("*** ");
write_strsignal (fd, signal);
WRITE_STRING ("\n");
#ifdef REGISTER_DUMP
REGISTER_DUMP;
#endif
WRITE_STRING ("\nBacktrace:\n");
/* Get the backtrace. */
arr = alloca (256 * sizeof (void *));
cnt = backtrace (arr, 256);
/* Now try to locate the PC from signal context in the backtrace.
Normally it will be found at arr[2], but it might appear later
if there were some signal handler wrappers. Allow a few bytes
difference to cope with as many arches as possible. */
pc = (uintptr_t) GET_PC (ctx);
for (i = 0; i < cnt; ++i)
if ((uintptr_t) arr[i] >= pc - 16 && (uintptr_t) arr[i] <= pc + 16)
break;
/* If we haven't found it, better dump full backtrace even including
the signal handler frames instead of not dumping anything. */
if (i == cnt)
i = 0;
/* Now generate nicely formatted output. */
__backtrace_symbols_fd (arr + i, cnt - i, fd);
#ifdef HAVE_PROC_SELF
/* Now the link map. */
int mapfd = open ("/proc/self/maps", O_RDONLY);
if (mapfd != -1)
{
write (fd, "\nMemory map:\n\n", 14);
char buf[256];
ssize_t n;
while ((n = TEMP_FAILURE_RETRY (read (mapfd, buf, sizeof (buf)))) > 0)
TEMP_FAILURE_RETRY (write (fd, buf, n));
close (mapfd);
}
#endif
/* Pass on the signal (so that a core file is produced). */
sa.sa_handler = SIG_DFL;
sigemptyset (&sa.sa_mask);
sa.sa_flags = 0;
sigaction (signal, &sa, NULL);
raise (signal);
}
static void
__attribute__ ((constructor))
install_handler (void)
{
struct sigaction sa;
const char *sigs = getenv ("SEGFAULT_SIGNALS");
const char *name;
sa.sa_handler = (void *) catch_segfault;
sigemptyset (&sa.sa_mask);
sa.sa_flags = SA_RESTART;
/* Maybe we are expected to use an alternative stack. */
if (getenv ("SEGFAULT_USE_ALTSTACK") != 0)
{
void *stack_mem = malloc (2 * SIGSTKSZ);
stack_t ss;
if (stack_mem != NULL)
{
ss.ss_sp = stack_mem;
ss.ss_flags = 0;
ss.ss_size = 2 * SIGSTKSZ;
if (sigaltstack (&ss, NULL) == 0)
sa.sa_flags |= SA_ONSTACK;
}
}
if (sigs == NULL)
sigaction (SIGSEGV, &sa, NULL);
else if (sigs[0] == '\0')
/* Do not do anything. */
return;
else
{
const char *where;
int all = __strcasecmp (sigs, "all") == 0;
#define INSTALL_FOR_SIG(sig, name) \
where = __strcasestr (sigs, name); \
if (all || (where != NULL \
&& (where == sigs || !isalnum (where[-1])) \
&& !isalnum (where[sizeof (name) - 1]))) \
sigaction (sig, &sa, NULL);
INSTALL_FOR_SIG (SIGSEGV, "segv");
INSTALL_FOR_SIG (SIGILL, "ill");
#ifdef SIGBUS
INSTALL_FOR_SIG (SIGBUS, "bus");
#endif
#ifdef SIGSTKFLT
INSTALL_FOR_SIG (SIGSTKFLT, "stkflt");
#endif
INSTALL_FOR_SIG (SIGABRT, "abrt");
INSTALL_FOR_SIG (SIGFPE, "fpe");
}
/* Preserve the output file name if there is any given. */
name = getenv ("SEGFAULT_OUTPUT_NAME");
if (name != NULL && name[0] != '\0')
{
int ret = access (name, R_OK | W_OK);
if (ret == 0 || (ret == -1 && errno == ENOENT))
fname = __strdup (name);
}
}
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