[PATCH 2/2 v3] Demangler crash handler

[Gary Benson <gbenson at redhat dot com>]

This patch wraps calls to the demangler with a segmentation fault
handler.  The first time a segmentation fault is caught a core file
is generated and the user is prompted to file a bug and offered the
choice to exit or to continue their GDB session.  A maintainence
option is provided to allow the user to disable the crash handler
if required.

Eli pointed out that SIGSEGV is an ANSI-standard signal but I found
various other SIGSEGV checks in GDB so I have left the preprocessor
conditionals intact for consistency.  I hope this is ok.


gdb/
2014-06-04  Gary Benson  <gbenson@redhat.com>

	* utils.h (dump_core): New declaration.
	* utils.c (dump_core): Make non-static.
	* cp-support.c (signal.h): New include.
	(catch_demangler_crashes): New flag.
	(SIGJMP_BUF): New define.
	(SIGSETJMP): Likewise.
	(SIGLONGJMP): Likewise.
	(gdb_demangle_jmp_buf): New static global.
	(gdb_demangle_signal_handler): New function.
	(gdb_demangle): If catch_demangler_crashes is set, install the
	above signal handler before calling bfd_demangle, and restore
	the original signal handler afterwards.  Display the offending
	symbol and call demangler_warning the first time a segmentation
	fault is caught.
	(_initialize_cp_support): New maint set/show command.

gdb/doc/
2014-06-04  Gary Benson  <gbenson@redhat.com>

	* gdb.texinfo (Maintenance Commands): Document new
	"maint set/show catch-demangler-crashes" option.

diff --git a/gdb/utils.h b/gdb/utils.h
index 31f9c19..8ada98e 100644
--- a/gdb/utils.h
+++ b/gdb/utils.h
@@ -374,4 +374,8 @@ extern ULONGEST align_down (ULONGEST v, int n);
 
 extern LONGEST gdb_sign_extend (LONGEST value, int bit);
 
+/* Dump core trying to increase the core soft limit to hard limit first.  */
+
+extern void dump_core (void);
+
 #endif /* UTILS_H */
diff --git a/gdb/utils.c b/gdb/utils.c
index 686b153..733c697 100644
--- a/gdb/utils.c
+++ b/gdb/utils.c
@@ -600,7 +600,7 @@ error_stream (struct ui_file *stream)
 
 /* Dump core trying to increase the core soft limit to hard limit first.  */
 
-static void
+void
 dump_core (void)
 {
 #ifdef HAVE_SETRLIMIT
diff --git a/gdb/cp-support.c b/gdb/cp-support.c
index 91533e8..96f7d89 100644
--- a/gdb/cp-support.c
+++ b/gdb/cp-support.c
@@ -36,6 +36,7 @@
 #include "value.h"
 #include "cp-abi.h"
 #include "language.h"
+#include <signal.h>
 
 #include "safe-ctype.h"
 
@@ -1505,12 +1506,111 @@ cp_lookup_rtti_type (const char *name, struct block *block)
   return rtti_type;
 }
 
+#if defined (SIGSEGV) && defined (HAVE_WORKING_FORK)
+
+/* If nonzero, attempt to catch crashes in the demangler and print
+   useful debugging information.  */
+
+static int catch_demangler_crashes = 1;
+
+/* Wrap set/long jmp so that it's more portable.  */
+
+#if defined(HAVE_SIGSETJMP)
+#define SIGJMP_BUF		sigjmp_buf
+#define SIGSETJMP(buf)		sigsetjmp((buf), 1)
+#define SIGLONGJMP(buf,val)	siglongjmp((buf), (val))
+#else
+#define SIGJMP_BUF		jmp_buf
+#define SIGSETJMP(buf)		setjmp(buf)
+#define SIGLONGJMP(buf,val)	longjmp((buf), (val))
+#endif
+
+/* Stack context and environment for demangler crash recovery.  */
+
+static SIGJMP_BUF gdb_demangle_jmp_buf;
+
+/* Signal handler for gdb_demangle.  */
+
+static void
+gdb_demangle_signal_handler (int signo)
+{
+  static int core_dumped = 0;
+
+  if (!core_dumped)
+    {
+      if (fork () == 0)
+	dump_core ();
+
+      core_dumped = 1;
+    }
+
+  SIGLONGJMP (gdb_demangle_jmp_buf, signo);
+}
+
+#endif
+
 /* A wrapper for bfd_demangle.  */
 
 char *
 gdb_demangle (const char *name, int options)
 {
-  return bfd_demangle (NULL, name, options);
+  char *result = NULL;
+  int crash_signal = 0;
+
+#if defined (SIGSEGV) && defined (HAVE_WORKING_FORK)
+#if defined (HAVE_SIGACTION) && defined (SA_RESTART)
+  struct sigaction sa, old_sa;
+
+  if (catch_demangler_crashes)
+    {
+      sa.sa_handler = gdb_demangle_signal_handler;
+      sigemptyset (&sa.sa_mask);
+      sa.sa_flags = 0;
+      sigaction (SIGSEGV, &sa, &old_sa);
+    }
+#else
+  void (*ofunc) ();
+
+  if (catch_demangler_crashes)
+    ofunc = (void (*)()) signal (SIGSEGV, gdb_demangle_signal_handler);
+#endif
+
+  if (catch_demangler_crashes)
+    crash_signal = SIGSETJMP (gdb_demangle_jmp_buf);
+#endif
+
+  if (crash_signal == 0)
+    result = bfd_demangle (NULL, name, options);
+
+#if defined (SIGSEGV) && defined (HAVE_WORKING_FORK)
+  if (catch_demangler_crashes)
+    {
+#if defined (HAVE_SIGACTION) && defined (SA_RESTART)
+      sigaction (SIGSEGV, &old_sa, NULL);
+#else
+      signal (SIGSEGV, ofunc);
+#endif
+
+      if (crash_signal != 0)
+	{
+	  static int error_reported = 0;
+
+	  if (!error_reported)
+	    {
+	      demangler_warning (__FILE__, __LINE__,
+				 _("unable to demangle '%s' "
+				   "(demangler failed with signal %d)"),
+				 name, crash_signal);
+
+	      error_reported = 1;
+	    }
+
+	  result = NULL;
+	}
+    }
+#endif
+
+  return result;
 }
 
 /* Don't allow just "maintenance cplus".  */
@@ -1585,4 +1685,17 @@ _initialize_cp_support (void)
 Usage: info vtbl EXPRESSION\n\
 Evaluate EXPRESSION and display the virtual function table for the\n\
 resulting object."));
+
+#if defined (SIGSEGV) && defined (HAVE_WORKING_FORK)
+  add_setshow_boolean_cmd ("catch-demangler-crashes", class_maintenance,
+			   &catch_demangler_crashes, _("\
+Set whether to attempt to catch demangler crashes."), _("\
+Show whether to attempt to catch demangler crashes."), _("\
+If enabled GDB will attempt to catch demangler crashes and\n\
+display the offending symbol."),
+			   NULL,
+			   NULL,
+			   &maintenance_set_cmdlist,
+			   &maintenance_show_cmdlist);
+#endif
 }
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 6104f55..6b39452 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -33235,6 +33235,17 @@ Expand symbol tables.
 If @var{regexp} is specified, only expand symbol tables for file
 names matching @var{regexp}.
 
+@kindex maint set catch-demangler-crashes
+@kindex maint show catch-demangler-crashes
+@cindex demangler crashes
+@item maint set catch-demangler-crashes [on|off]
+@itemx maint show catch-demangler-crashes
+Control whether @value{GDBN} should attempt to catch crashes in the
+symbol name demangler.  The default is to attempt to catch crashes.
+If enabled, the first time a crash is caught, a core file is created,
+the offending symbol is displayed and the user is presented with the
+option to terminate the current session.
+
 @kindex maint cplus first_component
 @item maint cplus first_component @var{name}
 Print the first C@t{++} class/namespace component of @var{name}.