Armin Rigo's fix & test for

[ 729622 ] line tracing hook errors

with massaging from me to integrate test into test suite.

Lib/test/test_trace.py

@@ -221,6 +221,27 @@ class RaisingTraceFuncTestCase(unittest.TestCase):
     def test_exception(self):
         self.run_test_for_event('exception')
 
+    def test_trash_stack(self):
+        def f():
+            for i in range(5):
+                print i  # line tracing will raise an exception at this line
+
+        def g(frame, why, extra):
+            if (why == 'line' and
+                frame.f_lineno == f.func_code.co_firstlineno + 2):
+                raise RuntimeError, "i am crashing"
+            return g
+
+        sys.settrace(g)
+        try:
+            f()
+        except RuntimeError:
+            # the test is really that this doesn't segfault:
+            import gc
+            gc.collect()
+        else:
+            self.fail("exception not propagated")
+
 
 # 'Jump' tests: assigning to frame.f_lineno within a trace function
 # moves the execution position - it's how debuggers implement a Jump

Python/ceval.c

@@ -819,18 +819,19 @@ eval_frame(PyFrameObject *f)
 			   for expository comments */
 			f->f_stacktop = stack_pointer;
 			
-			if (maybe_call_line_trace(tstate->c_tracefunc,
-						  tstate->c_traceobj,
-						  f, &instr_lb, &instr_ub)) {
+			err = maybe_call_line_trace(tstate->c_tracefunc,
+						    tstate->c_traceobj,
+						    f, &instr_lb, &instr_ub);
+			/* Reload possibly changed frame fields */
+			JUMPTO(f->f_lasti);
+			if (f->f_stacktop != NULL) {
+				stack_pointer = f->f_stacktop;
+				f->f_stacktop = NULL;
+			}
+			if (err) {
 				/* trace function raised an exception */
-				why = WHY_EXCEPTION;
 				goto on_error;
 			}
-			/* Reload possibly changed frame fields */
-			JUMPTO(f->f_lasti);
-			stack_pointer = f->f_stacktop;
-			assert(stack_pointer != NULL);
-			f->f_stacktop = NULL;
 		}
 
 		/* Extract opcode and argument */