[patch] handle nested exceptions

[dje at google dot com (Doug Evans)]

Hi.

We ran into a case where gdb was using a previously freed copy of e.message.
It's not enough to keep just last_message.

This patch creates a stack of messages.

I will check this in in a few days if there are no objections.

2011-12-14  Doug Evans  <dje@google.com>

	* exceptions.c (catcher_list_size): New function.
	(last_message): Delete.
	(exception_messages, exception_messages_size): New static globals.
	(throw_it): Use exception_messages array to handle nested calls.

Index: exceptions.c
===================================================================
RCS file: /cvs/src/src/gdb/exceptions.c,v
retrieving revision 1.48
diff -u -p -r1.48 exceptions.c
--- exceptions.c	26 Aug 2011 21:45:22 -0000	1.48
+++ exceptions.c	9 Dec 2011 19:54:36 -0000
@@ -68,6 +68,22 @@ struct catcher
 /* Where to go for throw_exception().  */
 static struct catcher *current_catcher;
 
+/* Return length of current_catcher list.  */
+
+static int
+catcher_list_size (void)
+{
+  int size;
+  struct catcher *catcher;
+
+  for (size = 0, catcher = current_catcher;
+       catcher != NULL;
+       catcher = catcher->prev)
+    ++size;
+
+  return size;
+}
+
 EXCEPTIONS_SIGJMP_BUF *
 exceptions_state_mc_init (volatile struct gdb_exception *exception,
 			  return_mask mask)
@@ -220,8 +236,6 @@ throw_exception (struct gdb_exception ex
   EXCEPTIONS_SIGLONGJMP (current_catcher->buf, exception.reason);
 }
 
-static char *last_message;
-
 void
 deprecated_throw_reason (enum return_reason reason)
 {
@@ -359,23 +373,48 @@ print_any_exception (struct ui_file *fil
     }
 }
 
+/* A stack of exception messages.
+   This is needed to handle nested calls to throw_it: we don't want to
+   xfree space for a message before it's used.
+   It is indexed by the size of the current_catcher list.
+   This is a dynamically allocated array so that we don't care how deeply
+   GDB nests its TRY_CATCHs.  */
+static char **exception_messages;
+/* The number of currently allocated entries in exception_messages.  */
+static int exception_messages_size;
+
 static void ATTRIBUTE_NORETURN ATTRIBUTE_PRINTF (3, 0)
 throw_it (enum return_reason reason, enum errors error, const char *fmt,
 	  va_list ap)
 {
   struct gdb_exception e;
   char *new_message;
+  int depth = catcher_list_size ();
+
+  gdb_assert (depth > 0);
 
-  /* Save the message.  Create the new message before deleting the
-     old, the new message may include the old message text.  */
+  /* Note: The new message may use an old message's text.  */
   new_message = xstrvprintf (fmt, ap);
-  xfree (last_message);
-  last_message = new_message;
+
+  if (depth > exception_messages_size)
+    {
+      int old_size = exception_messages_size;
+
+      exception_messages_size = depth + 10;
+      exception_messages = (char **) xrealloc (exception_messages,
+					       exception_messages_size
+					       * sizeof (char *));
+      memset (exception_messages + old_size, 0,
+	      (exception_messages_size - old_size) * sizeof (char *));
+    }
+
+  xfree (exception_messages[depth - 1]);
+  exception_messages[depth - 1] = new_message;
 
   /* Create the exception.  */
   e.reason = reason;
   e.error = error;
-  e.message = last_message;
+  e.message = new_message;
 
   /* Throw the exception.  */
   throw_exception (e);