[3.14] gh-140104: Set next_instr properly in the JIT during exceptions (GH-140233) (GH-140687)

Co-authored-by: Ken Jin <kenjin@python.org>
Co-authored-by: devdanzin <74280297+devdanzin@users.noreply.github.com>
Co-authored-by: Chris Eibl <138194463+chris-eibl@users.noreply.github.com>

Lib/test/test_capi/test_opt.py

@@ -1972,6 +1972,27 @@ def testfunc(n):
         assert ex is not None
         """))
 
+    def test_next_instr_for_exception_handler_set(self):
+        # gh-140104: We just want the exception to be caught properly.
+        def f():
+            for i in range(TIER2_THRESHOLD + 3):
+                try:
+                    undefined_variable(i)
+                except Exception:
+                    pass
+
+        f()
+
+    def test_next_instr_for_exception_handler_set_lasts_instr(self):
+        # gh-140104: We just want the exception to be caught properly.
+        def f():
+            a_list = []
+            for _ in range(TIER2_THRESHOLD + 3):
+                try:
+                    a_list[""] = 0
+                except Exception:
+                    pass
+
 
 def global_identity(x):
     return x

Misc/NEWS.d/next/Core_and_Builtins/2025-10-16-21-47-00.gh-issue-140104.A8SQIm.rst

@@ -0,0 +1,2 @@
+Fix a bug with exception handling in the JIT. Patch by Ken Jin. Bug reported
+by Daniel Diniz.

Python/ceval_macros.h

@@ -368,7 +368,9 @@ do {                                                   \
     frame = tstate->current_frame;                     \
     stack_pointer = _PyFrame_GetStackPointer(frame);   \
     if (next_instr == NULL) {                          \
-        next_instr = frame->instr_ptr;                 \
+        /* gh-140104: The exception handler expects frame->instr_ptr
+            to after this_instr, not this_instr! */    \
+        next_instr = frame->instr_ptr + 1;             \
         JUMP_TO_LABEL(error);                          \
     }                                                  \
     DISPATCH();                                        \