[3.15] gh-161288: Fix perf trampoline crash on UBSan builds (GH-161294)

Include/pyport.h

@@ -573,6 +573,9 @@ extern "C" {
 #      define _Py_NO_SANITIZE_THREAD __attribute__((no_sanitize_thread))
 #    endif
 #  endif
+#  if __has_feature(undefined_behavior_sanitizer)
+#    define _Py_NO_SANITIZE_FUNCTION __attribute__((no_sanitize("function")))
+#  endif
 #elif defined(__GNUC__)
 #  if defined(__SANITIZE_ADDRESS__)
 #    define _Py_ADDRESS_SANITIZER
@@ -597,6 +600,9 @@ extern "C" {
 #ifndef _Py_NO_SANITIZE_MEMORY
 #  define _Py_NO_SANITIZE_MEMORY
 #endif
+#ifndef _Py_NO_SANITIZE_FUNCTION
+#  define _Py_NO_SANITIZE_FUNCTION
+#endif
 #ifndef _Py_MSAN_UNPOISON
 #  define _Py_MSAN_UNPOISON(PTR, SIZE)
 #endif

Lib/test/test_perf_profiler.py

@@ -17,10 +17,10 @@
 if not support.has_subprocess_support:
     raise unittest.SkipTest("test module requires subprocess")
 
-if support.check_sanitizer(address=True, memory=True, ub=True, function=True):
+if support.check_sanitizer(address=True, memory=True, function=False):
     # gh-109580: Skip the test because it does crash randomly if Python is
     # built with ASAN.
-    raise unittest.SkipTest("test crash randomly on ASAN/MSAN/UBSAN build")
+    raise unittest.SkipTest("test crash randomly on ASAN/MSAN build")
 
 
 def supports_trampoline_profiling():

Lib/test/test_samply_profiler.py

@@ -14,10 +14,10 @@
 if not support.has_subprocess_support:
     raise unittest.SkipTest("test module requires subprocess")
 
-if support.check_sanitizer(address=True, memory=True, ub=True, function=True):
+if support.check_sanitizer(address=True, memory=True, function=False):
     # gh-109580: Skip the test because it does crash randomly if Python is
     # built with ASAN.
-    raise unittest.SkipTest("test crash randomly on ASAN/MSAN/UBSAN build")
+    raise unittest.SkipTest("test crash randomly on ASAN/MSAN build")
 
 
 def supports_trampoline_profiling():

Misc/NEWS.d/next/Core_and_Builtins/2026-11-03-20-28-15.gh-issue-161288.LikC_U.rst

@@ -0,0 +1,3 @@
+Fix a crash in the perf trampoline (:option:`-X perf <-X>`) on builds with
+clang's ``-fsanitize=function``, which ``-fsanitize=undefined`` enables
+since clang 17.

Python/perf_trampoline.c

@@ -434,7 +434,8 @@ compile_trampoline(void)
     return code_arena_new_code(perf_code_arena);
 }
 
-static PyObject *
+// gh-161288: the trampoline has no -fsanitize=function type signature
+static PyObject * _Py_NO_SANITIZE_FUNCTION
 py_trampoline_evaluator(PyThreadState *ts, _PyInterpreterFrame *frame,
                         int throw)
 {