undefined behavior: tstate->datastack_top == NULL #96569
Description
I was chasing down some C trouble in code I had been experimenting. I used all the debug options I could find:
export CC="clang"
configure --with-assertions --with-address-sanitizer --with-trace-refs --with-undefined-behavior-sanitizer --with-pydebug
nice make -j8For sanity checking, I ran this on current main. I got:
../../Python/pystate.c:2199:27: runtime error: applying non-zero offset 112 to null pointer
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior ../../Python/pystate.c:2199:27 in
../../Python/pystate.c:2199:27: runtime error: applying non-zero offset 112 to null pointer
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior ../../Python/pystate.c:2199:27 in
../../Python/pystate.c:2199:27: runtime error: applying non-zero offset 112 to null pointer
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior ../../Python/pystate.c:2199:27 in
For a minimal reproducible example, have a look at my example PR that adds this check and fails to build:
diff --git a/Python/pystate.c b/Python/pystate.c
index a11f1622ecd..09543add9dd 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -2196,6 +2196,7 @@ _PyThreadState_PushFrame(PyThreadState *tstate, size_t size)
{
assert(size < INT_MAX/sizeof(PyObject *));
PyObject **base = tstate->datastack_top;
+ assert(base != NULL);
PyObject **top = base + size;
if (top >= tstate->datastack_limit) {
base = push_chunk(tstate, (int)size);Error messages
Enter any relevant error message caused by the crash, including a core dump if there is one.
I already pasted the error message I get from the sanitizers above. Here's the error message I get from my assertion instead (and building with just sequential make):
./Programs/_freeze_module zipimport ../../Lib/zipimport.py Python/frozen_modules/zipimport.h
./_bootstrap_python ../../Programs/_freeze_module.py abc ../../Lib/abc.py Python/frozen_modules/abc.h
_bootstrap_python: ../../Python/pystate.c:2199: _PyInterpreterFrame *_PyThreadState_PushFrame(PyThreadState *, size_t): Assertion `base != NULL' failed.
make: *** [Makefile:1238: Python/frozen_modules/abc.h] Aborted (core dumped)
Your environment
I tested this on Archlinux against latest main. You can also see it in action on the failed test run for my PR on github.