https://github.com/python/cpython/commit/cce38eefd4b8f4e90eaa40ebfda64cb5ffde679f commit: cce38eefd4b8f4e90eaa40ebfda64cb5ffde679f branch: 3.14 author: Miss Islington (bot) <[email protected]> committer: encukou <[email protected]> date: 2025-07-20T10:55:06+02:00 summary:
[3.14] Doc/c-api/memory.rst: extend --without-pymalloc doc with ASan information (GH-136790) (GH-136798) Extend the documentation for disabling pymalloc with the `--without-pymalloc` flag regarding why it is worth to use it when enabling AddressSanitizer for Python build (which is done, e.g., in CPython's CI builds). I have tested the CPython latest main build with both ASan and pymalloc enabled and it seems to work just fine. I did run the `python -m test` suite which didn't uncover any ASan crashes (though, it detected some memory leaks, which I believe are irrelevant here). I have discussed ASan and this flag with @encukou on the CPython Core sprint on EuroPython 2025. We initially thought that the `--without-pymalloc` flag is needed for ASan builds due to the fact pymalloc must hit the begining of page when determining if the memory to be freed comes from pymalloc or was allocated by the system malloc. In other words, we thought, that ASan would crash CPython during free of big objects (allocated by system malloc). It may be that this was the case in the past, but it is not the case anymore as the `address_in_range` function used by pymalloc is annotated to be skipped from the ASan instrumentation. (cherry picked from commit d19bb4471331ca2cb87b86e4c904bc9a2bafb044) Co-authored-by: Disconnect3d <[email protected]> Co-authored-by: Petr Viktorin <[email protected]> files: M Doc/c-api/memory.rst M Doc/using/configure.rst diff --git a/Doc/c-api/memory.rst b/Doc/c-api/memory.rst index 61fa49f8681cce..df1bb0ce370919 100644 --- a/Doc/c-api/memory.rst +++ b/Doc/c-api/memory.rst @@ -672,6 +672,10 @@ This allocator is disabled if Python is configured with the :option:`--without-pymalloc` option. It can also be disabled at runtime using the :envvar:`PYTHONMALLOC` environment variable (ex: ``PYTHONMALLOC=malloc``). +Typically, it makes sense to disable the pymalloc allocator when building +Python with AddressSanitizer (:option:`--with-address-sanitizer`) which helps +uncover low level bugs within the C code. + Customize pymalloc Arena Allocator ---------------------------------- diff --git a/Doc/using/configure.rst b/Doc/using/configure.rst index e5fe3c72b1b26e..2cda9587975ddc 100644 --- a/Doc/using/configure.rst +++ b/Doc/using/configure.rst @@ -802,6 +802,9 @@ Debug options .. option:: --with-address-sanitizer Enable AddressSanitizer memory error detector, ``asan`` (default is no). + To improve ASan detection capabilities you may also want to combine this + with :option:`--without-pymalloc` to disable the specialized small-object + allocator whose allocations are not tracked by ASan. .. versionadded:: 3.6 _______________________________________________ Python-checkins mailing list -- [email protected] To unsubscribe send an email to [email protected] https://mail.python.org/mailman3//lists/python-checkins.python.org Member address: [email protected]
