[3.14] gh-141579: Fix perf_jit backend in sys.activate_stack_trampoline() (GH-141580) (#141581)

Co-authored-by: Pablo Galindo Salgado <Pablogsal@gmail.com>

Lib/test/test_perf_profiler.py

@@ -231,6 +231,24 @@ class TestPerfTrampoline(unittest.TestCase):
                 """
         assert_python_ok("-c", code, PYTHON_JIT="0")
 
+    def test_sys_api_perf_jit_backend(self):
+        code = """if 1:
+                import sys
+                sys.activate_stack_trampoline("perf_jit")
+                assert sys.is_stack_trampoline_active() is True
+                sys.deactivate_stack_trampoline()
+                assert sys.is_stack_trampoline_active() is False
+                """
+        assert_python_ok("-c", code, PYTHON_JIT="0")
+
+    def test_sys_api_with_existing_perf_jit_trampoline(self):
+        code = """if 1:
+                import sys
+                sys.activate_stack_trampoline("perf_jit")
+                sys.activate_stack_trampoline("perf_jit")
+                """
+        assert_python_ok("-c", code, PYTHON_JIT="0")
+
 
 def is_unwinding_reliable_with_frame_pointers():
     cflags = sysconfig.get_config_var("PY_CORE_CFLAGS")

Misc/NEWS.d/next/Core_and_Builtins/2025-11-15-01-21-00.gh-issue-141579.aB7cD9.rst

@@ -0,0 +1,2 @@
+Fix :func:`sys.activate_stack_trampoline` to properly support the
+``perf_jit`` backend. Patch by Pablo Galindo.

Python/sysmodule.c

@@ -2373,6 +2373,7 @@ sys_activate_stack_trampoline_impl(PyObject *module, const char *backend)
                 return NULL;
             }
         }
+    }
     else if (strcmp(backend, "perf_jit") == 0) {
         _PyPerf_Callbacks cur_cb;
         _PyPerfTrampoline_GetCallbacks(&cur_cb);
@@ -2383,7 +2384,6 @@ sys_activate_stack_trampoline_impl(PyObject *module, const char *backend)
             }
         }
     }
-    }
     else {
         PyErr_Format(PyExc_ValueError, "invalid backend: %s", backend);
         return NULL;