Give more-useful info on a fatal error (Bug#12328).

* doc/emacs/trouble.texi (Crashing): New section, documenting this.
* etc/NEWS: Document the change.
* src/alloc.c [ENABLE_CHECKING]: Do not include <execinfo.h>.
(die) [ENABLE_CHECKING]: Call fatal_error_backtrace instead
of doing the work ourselves.
* src/emacs.c (fatal_error_signal): Let fatal_error_backtrace
do most of the work.
(fatal_error_backtrace): New function, taken from the guts
of the old fatal_error_signal, but with a new option to output
a backtrace.
(shut_down_emacs) [!DOS_NT]: Use strsignal to give more-useful
info about the signal than just its number.
* src/lisp.h (fatal_error_backtrace, emacs_backtrace): New decls.
* src/sysdep.c: Include <execinfo.h>
(emacs_backtrace): New function, taken partly from the previous
code of the 'die' function.
(emacs_abort): Call fatal_error_backtrace rather than abort.

5 files changed, 55 insertions, 10 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index b2634c4fdc4..ea3b3a92e01 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,22 @@
+2012-09-04  Paul Eggert  <eggert@cs.ucla.edu>
+
+        Give more-useful info on a fatal error (Bug#12328).
+        * alloc.c [ENABLE_CHECKING]: Do not include <execinfo.h>.
+        (die) [ENABLE_CHECKING]: Call fatal_error_backtrace instead
+        of doing the work ourselves.
+        * emacs.c (fatal_error_signal): Let fatal_error_backtrace
+        do most of the work.
+        (fatal_error_backtrace): New function, taken from the guts
+        of the old fatal_error_signal, but with a new option to output
+        a backtrace.
+        (shut_down_emacs) [!DOS_NT]: Use strsignal to give more-useful
+        info about the signal than just its number.
+        * lisp.h (fatal_error_backtrace, emacs_backtrace): New decls.
+        * sysdep.c: Include <execinfo.h>
+        (emacs_backtrace): New function, taken partly from the previous
+        code of the 'die' function.
+        (emacs_abort): Call fatal_error_backtrace rather than abort.
+
 2012-09-04  Stefan Monnier  <monnier@iro.umontreal.ca>
 
         * lread.c (readevalloop): Call internal-macroexpand-for-load to perform
diff --git a/src/alloc.c b/src/alloc.c
index 2a831cea62a..157d3a1d799 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -6685,21 +6685,14 @@ which_symbols (Lisp_Object obj, EMACS_INT find_max)
 
 #ifdef ENABLE_CHECKING
 
-# include <execinfo.h>
-
 bool suppress_checking;
 
 void
 die (const char *msg, const char *file, int line)
 {
-  enum { NPOINTERS_MAX = 500 };
-  void *buffer[NPOINTERS_MAX];
-  int npointers;
   fprintf (stderr, "\r\n%s:%d: Emacs fatal error: %s\r\n",
            file, line, msg);
-  npointers = backtrace (buffer, NPOINTERS_MAX);
-  backtrace_symbols_fd (buffer, npointers, STDERR_FILENO);
-  emacs_abort ();
+  fatal_error_backtrace (SIGABRT, INT_MAX);
 }
 #endif
 
diff --git a/src/emacs.c b/src/emacs.c
index b242cbf8844..18f249dc899 100644
--- a/src/emacs.c
+++ b/src/emacs.c
@@ -298,6 +298,14 @@ void
 fatal_error_signal (int sig)
 {
   SIGNAL_THREAD_CHECK (sig);
+  fatal_error_backtrace (sig, 10);
+}
+
+/* Report a fatal error due to signal SIG, output a backtrace of at
+   most BACKTRACE_LIMIT lines, and exit.  */
+_Noreturn void
+fatal_error_backtrace (int sig, int backtrace_limit)
+{
   fatal_error_code = sig;
   signal (sig, SIG_DFL);
 
@@ -312,6 +320,7 @@ fatal_error_signal (int sig)
         Fkill_emacs (make_number (sig));
 
       shut_down_emacs (sig, Qnil);
+      emacs_backtrace (backtrace_limit);
     }
 
   /* Signal the same code; this time it will really be fatal.
@@ -323,6 +332,9 @@ fatal_error_signal (int sig)
 #endif
 
   kill (getpid (), fatal_error_code);
+
+  /* This shouldn't be executed, but it prevents a warning.  */
+  exit (1);
 }
 
 #ifdef SIGDANGER
@@ -1992,7 +2004,7 @@ shut_down_emacs (int sig, Lisp_Object stuff)
       {
         reset_all_sys_modes ();
         if (sig && sig != SIGTERM)
-          fprintf (stderr, "Fatal error (%d)", sig);
+          fprintf (stderr, "Fatal error %d: %s", sig, strsignal (sig));
       }
   }
 #else
diff --git a/src/lisp.h b/src/lisp.h
index 0835795a26d..9ee9cd74b56 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -3266,6 +3266,7 @@ extern Lisp_Object Qfile_name_handler_alist;
 #ifdef FLOAT_CATCH_SIGILL
 extern void fatal_error_signal (int);
 #endif
+extern _Noreturn void fatal_error_backtrace (int, int);
 extern Lisp_Object Qkill_emacs;
 #if HAVE_SETLOCALE
 void fixup_locale (void);
@@ -3412,6 +3413,7 @@ extern int set_window_size (int, int, int);
 extern EMACS_INT get_random (void);
 extern void seed_random (void *, ptrdiff_t);
 extern void init_random (void);
+extern void emacs_backtrace (int);
 extern _Noreturn void emacs_abort (void) NO_INLINE;
 extern int emacs_open (const char *, int, int);
 extern int emacs_close (int);
diff --git a/src/sysdep.c b/src/sysdep.c
index 78164a8f02a..1f4de194c64 100644
--- a/src/sysdep.c
+++ b/src/sysdep.c
@@ -21,6 +21,7 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
 #define SYSTIME_INLINE EXTERN_INLINE
 
+#include <execinfo.h>
 #include <signal.h>
 #include <stdio.h>
 #include <setjmp.h>
@@ -1856,12 +1857,30 @@ snprintf (char *buf, size_t bufsize, char const *format, ...)
 }
 #endif
 
+/* If a backtrace is available, output the top lines of it to stderr.
+   Do not output more than BACKTRACE_LIMIT or BACKTRACE_LIMIT_MAX lines.
+   This function may be called from a signal handler, so it should
+   not invoke async-unsafe functions like malloc.  */
+void
+emacs_backtrace (int backtrace_limit)
+{
+  enum { BACKTRACE_LIMIT_MAX = 500 };
+  void *buffer[BACKTRACE_LIMIT_MAX + 1];
+  int bounded_limit = min (backtrace_limit, BACKTRACE_LIMIT_MAX);
+  int npointers = backtrace (buffer, bounded_limit + 1);
+  if (npointers)
+    ignore_value (write (STDERR_FILENO, "\nBacktrace:\n", 12));
+  backtrace_symbols_fd (buffer, bounded_limit, STDERR_FILENO);
+  if (bounded_limit < npointers)
+    ignore_value (write (STDERR_FILENO, "...\n", 4));
+}
+
 #ifndef HAVE_NTGUI
 /* Using emacs_abort lets GDB return from a breakpoint here.  */
 void
 emacs_abort (void)
 {
-  abort ();
+  fatal_error_backtrace (SIGABRT, 10);
 }
 #endif