Fix bug introduced by SF patch #643835, Set Next Statement for Python debuggers

blockstack_top could be 0 when blockstack[blockstack_top-1]
was referenced (ie blockstack[-1]) which crashed on hpux.
Patch & fix by Richie Hindle

diff --git a/Objects/frameobject.c b/Objects/frameobject.c
index b9a481224f871f938478bbab0f955a65a0956e85..9123d94283edc96361903d5f5ade8753a77f1da9 100644 (file)
--- a/Objects/frameobject.c
+++ b/Objects/frameobject.c
@@ -184,6 +184,7 @@ frame_setlineno(PyFrameObject *f, PyObject* p_new_lineno)
                        break;
 
                case POP_BLOCK:
+                       assert(blockstack_top > 0);
                        setup_op = code[blockstack[blockstack_top-1]];
                        if (setup_op == SETUP_FINALLY) {
                                in_finally[blockstack_top-1] = 1;
@@ -196,10 +197,13 @@ frame_setlineno(PyFrameObject *f, PyObject* p_new_lineno)
                case END_FINALLY:
                        /* Ignore END_FINALLYs for SETUP_EXCEPTs - they exist
                         * in the bytecode but don't correspond to an actual
-                        * 'finally' block. */
-                       setup_op = code[blockstack[blockstack_top-1]];
-                       if (setup_op == SETUP_FINALLY) {
-                               blockstack_top--;
+                        * 'finally' block.  (If blockstack_top is 0, we must
+                        * be seeing such an END_FINALLY.) */
+                       if (blockstack_top > 0) {
+                               setup_op = code[blockstack[blockstack_top-1]];
+                               if (setup_op == SETUP_FINALLY) {
+                                       blockstack_top--;
+                               }
                        }
                        break;
                }
@@ -233,6 +237,10 @@ frame_setlineno(PyFrameObject *f, PyObject* p_new_lineno)
                }
        }
 
+       /* Verify that the blockstack tracking code didn't get lost. */
+       assert(blockstack_top == 0);
+
+       /* After all that, are we jumping into / out of a 'finally' block? */
        if (new_lasti_setup_addr != f_lasti_setup_addr) {
                PyErr_SetString(PyExc_ValueError,
                            "can't jump into or out of a 'finally' block");