The problem seems to be that The problem is that PyFrame_LocalsToFast(frame, 1); calls into PyFrame_LocalsToFast where co->co_nlocals has a value of 3, and this causes co->co_cell2arg[i - co->co_nlocals]; to access outside the bounds of the array.

As this change is affecting all tests (there are many tests in the test suite that fail with a buffer overflow in the ASAN builds) I opened PR 26597 to revert commit commit631f9938b1604d4f893417ec339b9e0fa9196fb1. As always, please, recommit commit631f9938b1604d4f893417ec339b9e0fa9196fb1 once this issues are fixed.

To reproduce these failures locally you can:

$ export ASAN_OPTIONS=detect_leaks=0:allocator_may_return_null=1:handle_segv=0
$ ./configure --with-address-sanitizer --without-pymalloc
$ make -j -s
$ ./python -m test test_sys_settrac