This patch adds a new convenience variable called "$_exitsignal", which

will hold the signal number when the inferior terminates due to the
uncaught signal.

I've made modifications on infrun.c:handle_inferior_event such that
$_exitcode gets cleared when the inferior signalled, and vice-versa.
This assumption was made because the variables are mutually
exclusive, i.e., when the inferior terminates because of an uncaught
signal it is not possible for it to return.  I have also made modifications
such that when a corefile is loaded, $_exitsignal gets set to the uncaught
signal that "killed" the inferior, and $_exitcode is cleared.

The patch also adds a NEWS entry, documentation bits, and a testcase.  The
documentation entry explains how to use $_exitsignal and $_exitcode in a
GDB script, by making use of the new $_isvoid convenience function.

gdb/
2013-10-06  Sergio Durigan Junior  <sergiodj@redhat.com>

	* NEWS: Mention new convenience variable $_exitsignal.
	* corelow.c (core_open): Reset exit convenience variables.  Set
	$_exitsignal to the uncaught signal which generated the corefile.
	* infrun.c (handle_inferior_event): Reset exit convenience
	variables.  Set $_exitsignal for TARGET_WAITKIND_SIGNALLED.
	(clear_exit_convenience_vars): New function.
	* inferior.h (clear_exit_convenience_vars): New prototype.

gdb/testsuite/
2013-10-06  Sergio Durigan Junior  <sergiodj@redhat.com>

	* gdb.base/corefile.exp: Test whether $_exitsignal is set and
	$_exitcode is void when opening a corefile.
	* gdb.base/exitsignal.exp: New file.
	* gdb.base/segv.c: Likewise.
	* gdb.base/normal.c: Likewise.

gdb/doc/
2013-10-06  Sergio Durigan Junior  <sergiodj@redhat.com>

	* gdb.texinfo (Convenience Variables): Document $_exitsignal.
	Update entry for $_exitcode.

12 files changed, 308 insertions, 3 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 3d8d936..a433b46 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,13 @@
+2013-10-06  Sergio Durigan Junior  <sergiodj@redhat.com>
+
+	* NEWS: Mention new convenience variable $_exitsignal.
+	* corelow.c (core_open): Reset exit convenience variables.  Set
+	$_exitsignal to the uncaught signal which generated the corefile.
+	* infrun.c (handle_inferior_event): Reset exit convenience
+	variables.  Set $_exitsignal for TARGET_WAITKIND_SIGNALLED.
+	(clear_exit_convenience_vars): New function.
+	* inferior.h (clear_exit_convenience_vars): New prototype.
+
 2013-10-06  Yao Qi  <yao@codesourcery.com>
 
 	* varobj.h: Add comments to enum varobj_languages.
diff --git a/gdb/NEWS b/gdb/NEWS
index 737fa7e..8114fb1 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -122,6 +122,10 @@ show range-stepping
 * The exception-related catchpoints, like "catch throw", now accept a
   regular expression which can be used to filter exceptions by type.
 
+* The new convenience variable $_exitsignal is automatically set to
+  the terminating signal number when the program being debugged dies
+  due to an uncaught signal.
+
 * MI changes
 
   ** The -trace-save MI command can optionally save trace buffer in Common
diff --git a/gdb/corelow.c b/gdb/corelow.c
index 7a5aaab..d1e7f6a 100644
--- a/gdb/corelow.c
+++ b/gdb/corelow.c
@@ -429,6 +429,9 @@ core_open (char *filename, int from_tty)
   if (p)
     printf_filtered (_("Core was generated by `%s'.\n"), p);
 
+  /* Clearing any previous state of convenience variables.  */
+  clear_exit_convenience_vars ();
+
   siggy = bfd_core_file_failing_signal (core_bfd);
   if (siggy > 0)
     {
@@ -446,6 +449,11 @@ core_open (char *filename, int from_tty)
 
       printf_filtered (_("Program terminated with signal %s, %s.\n"),
 		       gdb_signal_to_name (sig), gdb_signal_to_string (sig));
+
+      /* Set the value of the internal variable $_exitsignal,
+	 which holds the signal uncaught by the inferior.  */
+      set_internalvar_integer (lookup_internalvar ("_exitsignal"),
+			       siggy);
     }
 
   /* Fetch all registers from core file.  */
diff --git a/gdb/doc/ChangeLog b/gdb/doc/ChangeLog
index 04e291b..89254a9 100644
--- a/gdb/doc/ChangeLog
+++ b/gdb/doc/ChangeLog
@@ -1,3 +1,8 @@
+2013-10-06  Sergio Durigan Junior  <sergiodj@redhat.com>
+
+	* gdb.texinfo (Convenience Variables): Document $_exitsignal.
+	Update entry for $_exitcode.
+
 2013-10-04  Joel Brobecker  <brobecker@adacore.com>
 
 	* gdb.texinfo (GDB/MI Program Execution): Document "-exec-run"'s
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index a68556b..7ec91d8 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -9751,8 +9751,64 @@ to match the format in which the data was printed.
 
 @item $_exitcode
 @vindex $_exitcode@r{, convenience variable}
-The variable @code{$_exitcode} is automatically set to the exit code when
-the program being debugged terminates.
+When the program being debugged terminates normally, @value{GDBN}
+automatically sets this variable to the exit code of the program, and
+resets @code{$_exitsignal} to @code{void}.
+
+@item $_exitsignal
+@vindex $_exitsignal@r{, convenience variable}
+When the program being debugged dies due to an uncaught signal,
+@value{GDBN} automatically sets this variable to that signal's number,
+and resets @code{$_exitcode} to @code{void}.
+
+To distinguish between whether the program being debugged has exited
+(i.e., @code{$_exitcode} is not @code{void}) or signalled (i.e.,
+@code{$_exitsignal} is not @code{void}), the convenience function
+@code{$_isvoid} can be used (@pxref{Convenience Funs,, Convenience
+Functions}).  For example, considering the following source code:
+
+@smallexample
+#include <signal.h>
+
+int
+main (int argc, char *argv[])
+@{
+  raise (SIGALRM);
+  return 0;
+@}
+@end smallexample
+
+A valid way of telling whether the program being debugged has exited
+or signalled would be:
+
+@smallexample
+(@value{GDBP}) define has_exited_or_signalled
+Type commands for definition of ``has_exited_or_signalled''.
+End with a line saying just ``end''.
+>if $_isvoid ($_exitsignal)
+ >echo The program has exited\n
+ >else
+ >echo The program has signalled\n
+ >end
+>end
+(@value{GDBP}) run
+Starting program:
+
+Program terminated with signal SIGALRM, Alarm clock.
+The program no longer exists.
+(@value{GDBP}) has_exited_or_signalled
+The program has signalled
+@end smallexample
+
+As can be seen, @value{GDBN} correctly informs that the program being
+debugged has signalled, since it calls @code{raise} and raises a
+@code{SIGALRM} signal.  If the program being debugged had not called
+@code{raise}, then @value{GDBN} would report a normal exit:
+
+@smallexample
+(@value{GDBP}) has_exited_or_signalled
+The program has exited
+@end smallexample
 
 @item $_exception
 The variable @code{$_exception} is set to the exception object being
diff --git a/gdb/inferior.h b/gdb/inferior.h
index 922a0f2..fff072b 100644
--- a/gdb/inferior.h
+++ b/gdb/inferior.h
@@ -224,6 +224,12 @@ extern void follow_inferior_reset_breakpoints (void);
 
 void set_step_info (struct frame_info *frame, struct symtab_and_line sal);
 
+/* Clear the convenience variables associated with the exit of the
+   inferior.  Currently, those variables are $_exitcode and
+   $_exitsignal.  */
+
+extern void clear_exit_convenience_vars (void);
+
 /* From infcmd.c */
 
 extern void post_create_inferior (struct target_ops *, int);
diff --git a/gdb/infrun.c b/gdb/infrun.c
index db0ad8d..39c9cf3 100644
--- a/gdb/infrun.c
+++ b/gdb/infrun.c
@@ -3426,6 +3426,9 @@ handle_inferior_event (struct execution_control_state *ecs)
       handle_vfork_child_exec_or_exit (0);
       target_terminal_ours ();	/* Must do this before mourn anyway.  */
 
+      /* Clearing any previous state of convenience variables.  */
+      clear_exit_convenience_vars ();
+
       if (ecs->ws.kind == TARGET_WAITKIND_EXITED)
 	{
 	  /* Record the exit code in the convenience variable $_exitcode, so
@@ -3440,7 +3443,34 @@ handle_inferior_event (struct execution_control_state *ecs)
 	  print_exited_reason (ecs->ws.value.integer);
 	}
       else
-	print_signal_exited_reason (ecs->ws.value.sig);
+	{
+	  struct regcache *regcache = get_thread_regcache (ecs->ptid);
+	  struct gdbarch *gdbarch = get_regcache_arch (regcache);
+
+	  if (gdbarch_gdb_signal_to_target_p (gdbarch))
+	    {
+	      /* Set the value of the internal variable $_exitsignal,
+		 which holds the signal uncaught by the inferior.  */
+	      set_internalvar_integer (lookup_internalvar ("_exitsignal"),
+				       gdbarch_gdb_signal_to_target (gdbarch,
+							  ecs->ws.value.sig));
+	    }
+	  else
+	    {
+	      /* We don't have access to the target's method used for
+		 converting between signal numbers (GDB's internal
+		 representation <-> target's representation).
+		 Therefore, we cannot do a good job at displaying this
+		 information to the user.  It's better to just warn
+		 her about it (if infrun debugging is enabled), and
+		 give up.  */
+	      if (debug_infrun)
+		fprintf_filtered (gdb_stdlog, _("\
+Cannot fill $_exitsignal with the correct signal number.\n"));
+	    }
+
+	  print_signal_exited_reason (ecs->ws.value.sig);
+	}
 
       gdb_flush (gdb_stdout);
       target_mourn_inferior ();
@@ -7061,6 +7091,15 @@ save_inferior_ptid (void)
   *saved_ptid_ptr = inferior_ptid;
   return make_cleanup (restore_inferior_ptid, saved_ptid_ptr);
 }
+
+/* See inferior.h.  */
+
+void
+clear_exit_convenience_vars (void)
+{
+  clear_internalvar (lookup_internalvar ("_exitsignal"));
+  clear_internalvar (lookup_internalvar ("_exitcode"));
+}
 
 
 /* User interface for reverse debugging:
diff --git a/gdb/testsuite/ChangeLog b/gdb/testsuite/ChangeLog
index 4f07777..3a5a4e0 100644
--- a/gdb/testsuite/ChangeLog
+++ b/gdb/testsuite/ChangeLog
@@ -1,3 +1,11 @@
+2013-10-06  Sergio Durigan Junior  <sergiodj@redhat.com>
+
+	* gdb.base/corefile.exp: Test whether $_exitsignal is set and
+	$_exitcode is void when opening a corefile.
+	* gdb.base/exitsignal.exp: New file.
+	* gdb.base/segv.c: Likewise.
+	* gdb.base/normal.c: Likewise.
+
 2013-10-04  Joel Brobecker  <brobecker@adacore.com>
 
 	* gdb.mi/mi-start.c, gdb.mi/mi-start.exp: New files.
diff --git a/gdb/testsuite/gdb.base/corefile.exp b/gdb/testsuite/gdb.base/corefile.exp
index 04ae969..72c7a4a 100644
--- a/gdb/testsuite/gdb.base/corefile.exp
+++ b/gdb/testsuite/gdb.base/corefile.exp
@@ -142,6 +142,16 @@ gdb_test "print coremaker_ro" "\\\$$decimal = 201"
 
 gdb_test "print func2::coremaker_local" "\\\$$decimal = \\{0, 1, 2, 3, 4\\}"
 
+# Test the presence and the correct values of $_exitsignal and
+# $_exitcode variables.  The corefile is generated with a SIGABRT,
+# which is "6" in the Linux kernel.
+
+gdb_test "print \$_exitsignal" " = 6" \
+    "\$_exitsignal prints SIGABRT (6)"
+
+gdb_test "print \$_exitcode" " = void" \
+    "\$_exitcode is void"
+
 # Somehow we better test the ability to read the registers out of the core
 # file correctly.  I don't think the other tests do this.
 
diff --git a/gdb/testsuite/gdb.base/exitsignal.exp b/gdb/testsuite/gdb.base/exitsignal.exp
new file mode 100644
index 0000000..8687812
--- /dev/null
+++ b/gdb/testsuite/gdb.base/exitsignal.exp
@@ -0,0 +1,106 @@
+# Copyright 2013 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/>.
+
+# This test checks both $_exitcode and $_exitsignal variables.  The
+# purpose of this checking is to ensure that the variables are
+# mutually exclusive, i.e., that when $_exitsignal is set, $_exitcode
+# is not, and vice-versa.  This mutual exclusion happens because if an
+# inferior exited (either successfuly or not), it certainly was not
+# killed by a signal.  However, if it was killed by an uncaught
+# signal, then there is no way for it to have exited.
+
+if { [target_info exists gdb,nosignals] } {
+    verbose "Skipping exitsignal.exp because of nosignals."
+    continue
+}
+
+standard_testfile segv.c
+
+if { [prepare_for_testing ${testfile}.exp ${testfile} ${srcfile}] } {
+    return -1
+}
+
+# Run to main
+if { ![runto_main] } {
+    return -1
+}
+
+# Print $_exitsignal.  It should be void now, because nothing
+# happened.
+gdb_test "print \$_exitsignal" " = void" \
+    "\$_exitsignal is void before running"
+
+# Just to guarantee, making sure that $_exitcode is also void.
+gdb_test "print \$_exitcode" " = void" \
+    "\$_exitcode is void before running"
+
+# Trigger SIGSEGV.
+gdb_test "continue" "Program received signal SIGSEGV.*" "trigger SIGSEGV"
+
+# Continue until the end.
+gdb_test "continue" "Program terminated with signal SIGSEGV.*" \
+    "program terminated with SIGSEGV"
+
+# Now, print $_exitsignal again.  It should be 11 (SIGSEGV).
+gdb_test "print \$_exitsignal" " = 11" \
+    "\$_exitsignal is 11 (SIGSEGV) after SIGSEGV."
+
+# And $_exitcode should still be void, since the inferior died because
+# of a signal, and did not return.
+gdb_test "print \$_exitcode" " = void" \
+    "\$_exitcode is still void after SIGSEGV"
+
+# Re-run to main, i.e., restart the executable.
+rerun_to_main
+
+# Print the $_exitsignal again.  Even in this normal scenario, it
+# should still contain the signal triggered in the other run.
+gdb_test "print \$_exitsignal" " = 11" \
+    "\$_exitsignal is 11 (SIGSEGV) after restarting the inferior"
+
+# And, again, print $_exitcode.
+gdb_test "print \$_exitcode" " = void" \
+    "\$_exitcode is still void after restarting the inferior"
+
+# Now we test the behaviour of $_exit{code,signal} during a normal
+# inferior execution.
+standard_testfile normal.c
+
+if { [prepare_for_testing ${testfile}.exp ${testfile} ${srcfile}] } {
+    return -1
+}
+
+# Checking $_exitsignal and $_exitcode, both should be void before the
+# inferior is executed.
+gdb_test "print \$_exitsignal" " = void" \
+    "\$_exitsignal is void before normal inferior is executed"
+gdb_test "print \$_exitcode" " = void" \
+    "\$_exitcode is void before normal inferior is executed"
+
+# Run the inferior until the end.
+if { ![runto_main] } {
+    return -1
+}
+
+gdb_continue_to_end
+
+# Checking $_exitcode.  It should be 0.
+gdb_test "print \$_exitcode" " = 0" \
+    "\$_exitcode is zero after normal inferior is executed"
+
+# Checking $_exitsignal.  It should still be void, since the inferior
+# has not received any signal.
+gdb_test "print \$_exitsignal" " = void" \
+    "\$_exitsignal is still void after normal inferior is executed"
diff --git a/gdb/testsuite/gdb.base/normal.c b/gdb/testsuite/gdb.base/normal.c
new file mode 100644
index 0000000..4aa7c45
--- /dev/null
+++ b/gdb/testsuite/gdb.base/normal.c
@@ -0,0 +1,24 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2013 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/>.  */
+
+/* This test is just a normal return 0.  */
+
+int
+main (int argc, char *argv[])
+{
+  return 0;
+}
diff --git a/gdb/testsuite/gdb.base/segv.c b/gdb/testsuite/gdb.base/segv.c
new file mode 100644
index 0000000..8991f4d
--- /dev/null
+++ b/gdb/testsuite/gdb.base/segv.c
@@ -0,0 +1,29 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2013 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/>.  */
+
+/* This test can be used just to generate a SIGSEGV.  */
+
+#include <signal.h>
+
+int
+main (int argc, char *argv[])
+{
+  /* Generating a SIGSEGV.  */
+  raise (SIGSEGV);
+
+  return 0;
+}