[m-rev.] For review: Re-throw unhandled signals.

[Paul Bone]

For review by anyone.


Re-throw unhandled signals.

The Mercury runtime uses signal handlers to implement redzones and to provide
extra information in the case of a segmentation violation.  However this
prevents Mercury programs from dumping core.  It can also prevent the parent
process from knowing that the program was killed by a signal rather than exited
with exit status 1.  This change re-throws signals that cannot be handled so
that the program can dump core and does this compatibly with the existing
signal handlers.

runtime/mercury_memory_handlers.c:
    Use MR_reset_signal() and raise() to re-throw signals that we can't handle.

runtime/mercury_signal.h:
runtime/mercury_signal.c:
    Create MR_reset_signal() that resets the handler for a signal back to the
    default (SIG_DFL).

Index: runtime/mercury_memory_handlers.c
===================================================================
RCS file: /home/mercury1/repository/mercury/runtime/mercury_memory_handlers.c,v
retrieving revision 1.32
diff -u -p -b -r1.32 mercury_memory_handlers.c
--- runtime/mercury_memory_handlers.c	30 Oct 2007 00:46:22 -0000	1.32
+++ runtime/mercury_memory_handlers.c	13 May 2010 03:34:06 -0000
@@ -401,7 +401,8 @@ MR_explain_context(void *the_context)
     MR_print_dump_stack();
     MR_dump_prev_locations();
     fprintf(stderr, "exiting from signal handler\n");
-    exit(1);
+    MR_reset_signal(sig);
+    raise(sig);
 } /* end complex_sighandler() */
 
 #elif defined(MR_HAVE_SIGINFO_T)
@@ -480,7 +481,8 @@ complex_bushandler(int sig, siginfo_t *i
     MR_print_dump_stack();
     MR_dump_prev_locations();
     fprintf(stderr, "exiting from signal handler\n");
-    exit(1);
+    MR_reset_signal(sig);
+    raise(sig);
 } /* end complex_bushandler() */
 
 static void
@@ -557,7 +559,8 @@ complex_segvhandler(int sig, siginfo_t *
     MR_print_dump_stack();
     MR_dump_prev_locations();
     fprintf(stderr, "exiting from signal handler\n");
-    exit(1);
+    MR_reset_signal(sig);
+    raise(sig);
 } /* end complex_segvhandler */
 
 #else /* not MR_HAVE_SIGINFO_T && not MR_HAVE_SIGCONTEXT_STRUCT */
@@ -588,7 +591,8 @@ simple_sighandler(int sig)
     MR_print_dump_stack();
     MR_dump_prev_locations();
     fprintf(stderr, "exiting from signal handler\n");
-    exit(1);
+    MR_reset_signal(sig);
+    raise(sig);
 }
 
 #endif /* not MR_HAVE_SIGINFO_T && not MR_HAVE_SIGCONTEXT_STRUCT */
Index: runtime/mercury_signal.c
===================================================================
RCS file: /home/mercury1/repository/mercury/runtime/mercury_signal.c,v
retrieving revision 1.16
diff -u -p -b -r1.16 mercury_signal.c
--- runtime/mercury_signal.c	14 Nov 2006 00:15:41 -0000	1.16
+++ runtime/mercury_signal.c	13 May 2010 03:34:06 -0000
@@ -85,6 +85,26 @@ MR_do_setup_signal(int sig, MR_Code *han
 }
 
 void
+MR_reset_signal(int sig)
+{
+    MR_signal_action    act;
+
+#ifdef MR_HAVE_SIGACTION
+    if (sigemptyset(&(act.sa_mask)) != 0) {
+        MR_perror("cannot set clear signal mask");
+        exit(1);
+    }
+    errno = 0;
+
+    act.sa_flags = 0;
+    act.sa_handler = SIG_DFL;
+#else
+    act = SIG_DFL; 
+#endif
+    MR_set_signal_action(sig, &act, "Couldn't reset signal");
+}
+
+void
 MR_init_signal_action(MR_signal_action *act, MR_Code *handler,
     MR_bool need_info, MR_bool restart)
 {
Index: runtime/mercury_signal.h
===================================================================
RCS file: /home/mercury1/repository/mercury/runtime/mercury_signal.h,v
retrieving revision 1.14
diff -u -p -b -r1.14 mercury_signal.h
--- runtime/mercury_signal.h	20 Jun 2005 02:16:44 -0000	1.14
+++ runtime/mercury_signal.h	13 May 2010 03:34:06 -0000
@@ -81,6 +81,11 @@ extern	void	MR_setup_signal_no_restart(i
 			MR_bool need_info, const char * error_message);
 
 /*
+** Reset a signal to its default configuration.
+*/
+extern  void    MR_reset_signal(int sig);
+
+/*
 ** As above, but initialize a signal action suitable to be
 ** passed to MR_set_signal_action rather than setting a
 ** signal handler for a signal.
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