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[Patch, libfortran] PR 48931 Async-signal-safety of backtrace signal handler
- From: Janne Blomqvist <blomqvist dot janne at gmail dot com>
- To: GCC Patches <gcc-patches at gcc dot gnu dot org>, Fortran List <fortran at gcc dot gnu dot org>
- Date: Sat, 14 May 2011 22:40:20 +0300
- Subject: [Patch, libfortran] PR 48931 Async-signal-safety of backtrace signal handler
Hi,
the current version of showing the backtrace is not async-signal-safe
as it uses backtrace_symbols() which, in turn, uses malloc(). The
attached patch changes the backtrace printing functionality to instead
use backtrace_symbols_fd() and pipes.
Also, it does some other work on backtrace printing:
- Nowadays the main program has the same debug symbol name as whatever
the name of the main program is, rather than MAIN__. Therefore remove
special case logic related to that.
- Don't filter out stack frames from inside libgfortran, as this might
lose information in case the reason for the crash is in the library.
- Reformat the output slightly, so the each stack frame fits on one
line, and begins with #NUM, similar to GDB.
For instance, the small program
subroutine c
call abort ()
end subroutine c
subroutine b
call c
end subroutine b
subroutine a
call b
end subroutine a
program bt
call a
end program bt
compiled with -g -fno-whole-file now generates
Backtrace for this error:
#0 /home/janne/src/gfortran/trunk/install/lib64/libgfortran.so.3(+0x182b7)[0x7f9c8a2c42b7]
#1 /home/janne/src/gfortran/trunk/install/lib64/libgfortran.so.3(+0x19d07)[0x7f9c8a2c5d07]
#2 /home/janne/src/gfortran/trunk/install/lib64/libgfortran.so.3(+0xe1e49)[0x7f9c8a38de49]
#3 in b_ at bt.f90:5 (0x400612)
#4 in b_ at bt.f90:7 (0x400620)
#5 in a_ at bt.f90:11 (0x400630)
#6 in bt at bt.f90:15 (0x400640)
Aborted
In this case the 3 first frames are the output from
backtrace_symbols_fd() since addr2line can't get the symbols from
libgfortran. With static linking addr2line can see it:
Backtrace for this error:
#0 in _gfortrani_show_backtrace at backtrace.c:85 (0x405427)
#1 in _gfortrani_sys_abort at error.c:176 (0x4007B7)
#2 in _gfortran_abort (0x404469)
#3 in b_ at bt.f90:5 (0x400402)
#4 in b_ at bt.f90:7 (0x400410)
#5 in a_ at bt.f90:11 (0x400420)
#6 in bt at bt.f90:15 (0x400430)
Aborted
Regtested on x86_64-unknown-linux-gnu, Ok for trunk?
2011-05-14 Janne Blomqvist <jb@gcc.gnu.org>
PR libfortran/48931
* configure.ac: Check for backtrace_symbols_fd instead of
backtrace_symbols.
* config.h.in: Regenerated.
* configure: Regenerated.
* runtime/backtrace.c (local_strcasestr): Remove.
(bt_header): New function.
(dump_glibc_backtrace): Remove.
(show_backtrace): Rework to use backtrace_symbols_fd and pipes,
reformat output.
--
Janne Blomqvist
diff --git a/libgfortran/configure.ac b/libgfortran/configure.ac
index cf38fb0..9bb6210 100644
--- a/libgfortran/configure.ac
+++ b/libgfortran/configure.ac
@@ -267,7 +267,7 @@ AC_CHECK_FUNCS(localtime_r gmtime_r strerror_r getpwuid_r ttyname_r)
AC_CHECK_FUNCS(clock_gettime strftime)
# Check for glibc backtrace functions
-AC_CHECK_FUNCS(backtrace backtrace_symbols)
+AC_CHECK_FUNCS(backtrace backtrace_symbols_fd)
# Check libc for getgid, getpid, getuid
AC_CHECK_LIB([c],[getgid],[AC_DEFINE([HAVE_GETGID],[1],[libc includes getgid])])
diff --git a/libgfortran/runtime/backtrace.c b/libgfortran/runtime/backtrace.c
index 10917d3..ce1a0c7 100644
--- a/libgfortran/runtime/backtrace.c
+++ b/libgfortran/runtime/backtrace.c
@@ -54,56 +54,19 @@ see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
#define CAN_FORK (defined(HAVE_FORK) && defined(HAVE_EXECVP) \
&& defined(HAVE_WAIT))
#define GLIBC_BACKTRACE (defined(HAVE_BACKTRACE) \
- && defined(HAVE_BACKTRACE_SYMBOLS))
+ && defined(HAVE_BACKTRACE_SYMBOLS_FD))
#define CAN_PIPE (CAN_FORK && defined(HAVE_PIPE) \
&& defined(HAVE_DUP2) && defined(HAVE_FDOPEN) \
&& defined(HAVE_CLOSE))
-#if GLIBC_BACKTRACE && CAN_PIPE
-static char *
-local_strcasestr (const char *s1, const char *s2)
+/* GDB style #NUM index for each stack frame. */
+static void
+bt_header (int num)
{
-#ifdef HAVE_STRCASESTR
- return strcasestr (s1, s2);
-#else
-
- const char *p = s1;
- const size_t len = strlen (s2);
- const char u = *s2, v = isupper((int) *s2) ? tolower((int) *s2)
- : (islower((int) *s2) ? toupper((int) *s2)
- : *s2);
-
- while (1)
- {
- while (*p != u && *p != v && *p)
- p++;
- if (*p == 0)
- return NULL;
- if (strncasecmp (p, s2, len) == 0)
- return (char *)p;
- }
-#endif
+ st_printf (" #%d ", num);
}
-#endif
-
-
-#if GLIBC_BACKTRACE
-static void
-dump_glibc_backtrace (int depth, char *str[])
-{
- int i;
-
- for (i = 0; i < depth; i++)
- {
- estr_write (" + ");
- estr_write (str[i]);
- estr_write ("\n");
- }
- free (str);
-}
-#endif
/* show_backtrace displays the backtrace, currently obtained by means of
the glibc backtrace* functions. */
@@ -116,63 +79,49 @@ show_backtrace (void)
#define BUFSIZE 1024
void *trace[DEPTH];
- char **str;
int depth;
depth = backtrace (trace, DEPTH);
if (depth <= 0)
return;
- str = backtrace_symbols (trace, depth);
-
#if CAN_PIPE
-#ifndef STDIN_FILENO
-#define STDIN_FILENO 0
-#endif
-
-#ifndef STDOUT_FILENO
-#define STDOUT_FILENO 1
-#endif
-
-#ifndef STDERR_FILENO
-#define STDERR_FILENO 2
-#endif
-
/* We attempt to extract file and line information from addr2line. */
do
{
/* Local variables. */
- int f[2], pid, line, i;
+ int f[2], pid, line, bt[2], inp[2];
FILE *output;
- char addr_buf[DEPTH][GFC_XTOA_BUF_SIZE], func[BUFSIZE], file[BUFSIZE];
+ char addr_buf[GFC_XTOA_BUF_SIZE], func[BUFSIZE], file[BUFSIZE];
char *p, *end;
- const char *addr[DEPTH];
-
- /* Write the list of addresses in hexadecimal format. */
- for (i = 0; i < depth; i++)
- addr[i] = gfc_xtoa ((GFC_UINTEGER_LARGEST) (intptr_t) trace[i], addr_buf[i],
- sizeof (addr_buf[i]));
/* Don't output an error message if something goes wrong, we'll simply
fall back to the pstack and glibc backtraces. */
if (pipe (f) != 0)
break;
+ if (pipe (inp) != 0)
+ break;
if ((pid = fork ()) == -1)
break;
if (pid == 0)
{
/* Child process. */
-#define NUM_FIXEDARGS 5
- char *arg[DEPTH+NUM_FIXEDARGS+1];
+#define NUM_FIXEDARGS 7
+ char *arg[NUM_FIXEDARGS];
close (f[0]);
- close (STDIN_FILENO);
+
+ close (inp[1]);
+ if (dup2 (inp[0], STDIN_FILENO) == -1)
+ _exit (1);
+ close (inp[0]);
+
close (STDERR_FILENO);
if (dup2 (f[1], STDOUT_FILENO) == -1)
- _exit (0);
+ _exit (1);
close (f[1]);
arg[0] = (char *) "addr2line";
@@ -180,112 +129,133 @@ show_backtrace (void)
arg[2] = full_exe_path ();
arg[3] = (char *) "-f";
arg[4] = (char *) "-s";
- for (i = 0; i < depth; i++)
- arg[NUM_FIXEDARGS+i] = (char *) addr[i];
- arg[NUM_FIXEDARGS+depth] = NULL;
+ arg[5] = (char *) "-C";
+ arg[6] = NULL;
execvp (arg[0], arg);
- _exit (0);
+ _exit (1);
#undef NUM_FIXEDARGS
}
/* Father process. */
close (f[1]);
- wait (NULL);
+ close (inp[0]);
+ if (pipe (bt) != 0)
+ break;
+ backtrace_symbols_fd (trace, depth, bt[1]);
+ close (bt[1]);
output = fdopen (f[0], "r");
- i = -1;
- if (fgets (func, sizeof(func), output))
+ estr_write ("\nBacktrace for this error:\n");
+ for (int j = 0; j < depth; j++)
{
- estr_write ("\nBacktrace for this error:\n");
-
- do
+ const char *addr = gfc_xtoa
+ ((GFC_UINTEGER_LARGEST) (intptr_t) trace[j],
+ addr_buf, sizeof (addr_buf));
+
+ write (inp[1], addr, strlen (addr));
+ write (inp[1], "\n", 1);
+
+ if (! fgets (func, sizeof(func), output))
+ goto fallback;
+ if (! fgets (file, sizeof(file), output))
+ goto fallback;
+
+ for (p = func; *p != '\n' && *p != '\r'; p++)
+ ;
+ *p = '\0';
+
+ /* If we only have the address, use the glibc backtrace. */
+ if (func[0] == '?' && func[1] == '?' && file[0] == '?'
+ && file[1] == '?')
{
- if (! fgets (file, sizeof(file), output))
- goto fallback;
-
- i++;
-
- for (p = func; *p != '\n' && *p != '\r'; p++)
- ;
-
- *p = '\0';
-
- /* Try to recognize the internal libgfortran functions. */
- if (strncasecmp (func, "*_gfortran", 10) == 0
- || strncasecmp (func, "_gfortran", 9) == 0
- || strcmp (func, "main") == 0 || strcmp (func, "_start") == 0
- || strcmp (func, "_gfortrani_backtrace_handler") == 0)
- continue;
-
- if (local_strcasestr (str[i], "libgfortran.so") != NULL
- || local_strcasestr (str[i], "libgfortran.dylib") != NULL
- || local_strcasestr (str[i], "libgfortran.a") != NULL)
- continue;
-
- /* If we only have the address, use the glibc backtrace. */
- if (func[0] == '?' && func[1] == '?' && file[0] == '?'
- && file[1] == '?')
+ bt_header (j);
+ while (1)
{
- estr_write (" + ");
- estr_write (str[i]);
- estr_write ("\n");
- continue;
+ char bc;
+ ssize_t nread = read (bt[0], &bc, 1);
+ if (nread != 1 || bc == '\n')
+ break;
+ write (STDERR_FILENO, &bc, 1);
}
-
- /* Extract the line number. */
- for (end = NULL, p = file; *p; p++)
- if (*p == ':')
- end = p;
- if (end != NULL)
- {
- *end = '\0';
- line = atoi (++end);
- }
- else
- line = -1;
-
- if (strcmp (func, "MAIN__") == 0)
- estr_write (" + in the main program\n");
- else
- {
- estr_write (" + function ");
- estr_write (func);
- estr_write (" (0x");
- estr_write (addr[i]);
- estr_write (")\n");
- }
-
- if (line <= 0 && strcmp (file, "??") == 0)
- continue;
-
- if (line <= 0)
+ estr_write ("\n");
+ continue;
+ }
+ else
+ {
+ /* Forward to the next entry in the backtrace. */
+ while (1)
{
- estr_write (" from file ");
- estr_write (file);
- estr_write ("\n");
+ char bc;
+ ssize_t nread = read (bt[0], &bc, 1);
+ if (nread != 1 || bc == '\n')
+ break;
}
- else
- st_printf (" at line %d of file %s\n", line, file);
}
- while (fgets (func, sizeof(func), output));
- free (str);
- return;
+ /* _start is a setup routine that calls main(), and main() is
+ the frontend routine that calls some setup stuff and then
+ calls MAIN__, so at this point we should stop. */
+ if (strcmp (func, "_start") == 0 || strcmp (func, "main") == 0)
+ break;
+
+ /* Extract the line number. */
+ for (end = NULL, p = file; *p; p++)
+ if (*p == ':')
+ end = p;
+ if (end != NULL)
+ {
+ *end = '\0';
+ line = atoi (++end);
+ }
+ else
+ line = -1;
+
+ bt_header (j);
+ estr_write ("in ");
+ estr_write (func);
+
+ if (line <= 0 && strcmp (file, "??") == 0)
+ {
+ estr_write (" (0x");
+ estr_write (addr);
+ estr_write (")\n");
+ continue;
+ }
+
+ if (line <= 0)
+ {
+ estr_write (" at ");
+ estr_write (file);
+ }
+ else
+ st_printf (" at %s:%d", file, line);
+
+ estr_write (" (0x");
+ estr_write (addr);
+ estr_write (")\n");
+ } /* Loop over each hex address. */
+ close (inp[1]);
+ close (bt[0]);
+ wait (NULL);
+ return;
fallback:
- estr_write ("** Something went wrong while running addr2line. **\n"
- "** Falling back to a simpler backtrace scheme. **\n");
- }
- }
+ estr_write ("** Something went wrong while running addr2line. **\n"
+ "** Falling back to a simpler backtrace scheme. **\n");
+ }
while (0);
#undef DEPTH
#undef BUFSIZE
-#endif
-#endif
+#endif /* CAN_PIPE */
-#if CAN_FORK && defined(HAVE_GETPPID)
+ /* Fallback to the glibc backtrace. */
+ estr_write ("\nBacktrace for this error:\n");
+ backtrace_symbols_fd (trace, depth, STDERR_FILENO);
+ return;
+
+#elif defined(CAN_FORK) && defined(HAVE_GETPPID)
/* Try to call pstack. */
do
{
@@ -312,15 +282,9 @@ fallback:
execvp (arg[0], arg);
#undef NUM_ARGS
- /* pstack didn't work, so we fall back to dumping the glibc
- backtrace if we can. */
-#if GLIBC_BACKTRACE
- dump_glibc_backtrace (depth, str);
-#else
+ /* pstack didn't work. */
estr_write (" unable to produce a backtrace, sorry!\n");
-#endif
-
- _exit (0);
+ _exit (1);
}
/* Father process. */
@@ -328,13 +292,7 @@ fallback:
return;
}
while(0);
-#endif
-
-#if GLIBC_BACKTRACE
- /* Fallback to the glibc backtrace. */
- estr_write ("\nBacktrace for this error:\n");
- dump_glibc_backtrace (depth, str);
- return;
-#endif
+#else
estr_write ("\nBacktrace not yet available on this platform, sorry!\n");
+#endif
}