[patch] fix for crash in python pretty-printer

[ppluzhnikov@google.com (Paul Pluzhnikov)]

Greetings,

This is rather on the obvious side.
While debugging a buggy pretty-printer, GDB crashed on me:

Program received signal SIGSEGV, Segmentation fault.
0x000000000045db13 in do_my_cleanups (pmy_chain=0xa7c020, old_chain=0x1e65a10) at ../../gdb/utils.c:390
390           *pmy_chain = ptr->next;   /* Do this first incase recursion */

  ptr is NULL at that point.

(top) bt
#0  0x000000000045db13 in do_my_cleanups (pmy_chain=0xa7c020, old_chain=0x1e65a10) at ../../gdb/utils.c:390
#1  0x000000000045dadf in do_cleanups (...) at ../../gdb/utils.c:374
#2  0x00000000004d684b in apply_val_pretty_printer (...) at ../../gdb/python/python-prettyprint.c:526
#3  0x000000000051286a in value_print (...) at ../../gdb/valprint.c:388
#4  0x0000000000514f53 in print_formatted (...) at ../../gdb/printcmd.c:316
...

Attached is a fix (applies both to mainline and archer-tromey-python).
Tested on Linux/x86_64 with no regressions.

P.S. Is there an "easy" way to find such mis-uses of TRY_CATCH?
This one took me 2 hours to find :-(

Thanks,
--
Paul Pluzhnikov

2009-07-07  Paul Pluzhnikov  <ppluzhnikov@google.com>

	* python/python-value.c (valpy_getitem): Don't return from TRY_CATCH.

diff --git a/gdb/python/python-value.c b/gdb/python/python-value.c
index 8c85ef6..489b65b 100644
--- a/gdb/python/python-value.c
+++ b/gdb/python/python-value.c
@@ -290,8 +290,7 @@ valpy_getitem (PyObject *self, PyObject *key)
 {
   value_object *self_value = (value_object *) self;
   char *field = NULL;
-  struct value *idx = NULL;
-  struct value *res_val = NULL;	  /* Initialize to appease gcc warning.  */
+  struct value *res_val = NULL;
   volatile struct gdb_exception except;
 
   if (gdbpy_is_string (key))
@@ -313,12 +312,17 @@ valpy_getitem (PyObject *self, PyObject *key)
 	     value code throw an exception if the index has an invalid
 	     type.  */
 	  struct value *idx = convert_value_from_python (key);
-	  if (idx == NULL)
-	    return NULL;
-
-	  res_val = value_subscript (tmp, value_as_long (idx));
+	  if (idx != NULL)
+	    res_val = value_subscript (tmp, value_as_long (idx));
 	}
     }
+
+  if (res_val == NULL)
+    {
+      gdb_assert (field == NULL);
+      return NULL;
+    }
+
   if (field)
     xfree (field);
   GDB_PY_HANDLE_EXCEPTION (except);