build: big endian ARM builds fail with mimalloc enabled

[vfazio]

Bug report

Bug description:

Preface: I'm aware that big-endian ARM is not listed in PEP 11 where it's assumed that binaries are little endian by default.

I wrote an upstream issue to track this as well: microsoft/mimalloc#1046

build log: https://autobuild.buildroot.org/results/26b752738022e8b46e810a08e28d687120e5c4e3/build-end.log

/home/autobuild/autobuild/instance-4/output-1/per-package/python3/host/bin/armeb-buildroot-linux-gnueabi-gcc  -fno-strict-overflow -Wsign-compare -DNDEBUG -g -O3 -Wall -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64  -Ofast -g2 -D_FORTIFY_SOURCE=1   -std=c11 -Wextra -Wno-unused-parameter -Wno-missing-field-initializers -Wstrict-prototypes -Werror=implicit-function-declaration -fvisibility=hidden  -I./Include/internal -I./Include/internal/mimalloc  -I. -I./Include -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64  -fPIC -DPy_BUILD_CORE_BUILTIN -c ./Modules/_abc.c -o Modules/_abc.o
In file included from ./Include/internal/mimalloc/mimalloc/types.h:24,
                 from ./Include/internal/pycore_mimalloc.h:44,
                 from ./Include/internal/pycore_interp.h:31,
                 from ./Include/internal/pycore_runtime.h:17,
                 from ./Include/internal/pycore_emscripten_trampoline.h:4,
                 from ./Include/internal/pycore_object.h:13,
                 from ./Modules/_abc.c:8:
./Include/internal/mimalloc/mimalloc/atomic.h:83:20: warning: 'mi_atomic_yield' declared 'static' but never defined [-Wunused-function]
   83 | static inline void mi_atomic_yield(void);
      |                    ^~~~~~~~~~~~~~~

This prevents CPython from linking correctly:

/home/autobuild/autobuild/instance-4/output-1/per-package/python3/host/bin/armeb-buildroot-linux-gnueabi-gcc -shared     -Wl,--no-as-needed -o libpython3.so -Wl,-hlibpython3.so libpython3.13.so
/home/autobuild/autobuild/instance-4/output-1/per-package/python3/host/bin/armeb-buildroot-linux-gnueabi-gcc     -Xlinker -export-dynamic -o python Programs/python.o -L. -lpython3.13 -ldl  -lpthread -latomic                          -lm 
/home/autobuild/autobuild/instance-4/output-1/per-package/python3/host/bin/../lib/gcc/armeb-buildroot-linux-gnueabi/13.3.0/../../../../armeb-buildroot-linux-gnueabi/bin/ld: ./libpython3.13.so: undefined reference to `mi_atomic_yield'
collect2: error: ld returned 1 exit status
make[1]: *** [Makefile:1024: python] Error 1

The quick fix may be as simple as changing the __ARM_ARCH__ -> __ARM_ARCH macro reference, but I'm waiting on input from upstream

---

Workarounds: disable mimalloc

CPython versions tested on:

3.13

Operating systems tested on:

Linux

Linked PRs

• gh-131675: mimalloc: fix mi_atomic_yield on 32-bit ARM #131784
• [3.13] gh-131675: Fix mi_atomic_yield in mimalloc on 32-bit ARM (gh-131784) #131954

[colesbury]

If you put up a PR, I'd be happy to review it.

[vfazio]

If you put up a PR, I'd be happy to review it.

In this repo or upstream?

[colesbury]

In this repo

[vfazio]

In this repo

Cool, I'll spin something up in the next few days once I've had a chance to test it.

I don't have a cross clang readily available to see what predefines it specifies, i imagine it largely follows suit with GCC.

It looks like the only 32bit ARM platform in PEP 11 is armv7l for RPi which is tier 3, but I'm not sure CPython has 32bit ARM in its CI so the fix "working" may not be evident from the pipelines.

[colesbury]

You can check clang behavior with something like: https://gcc.godbolt.org/z/fdbezs1EK

We have a Raspbian buildbot. It's part of the overall CPython CI, but not through GitHub actions. It looks like it currently targets armv8l-unknown-linux-gnueabihf, which is still 32-bit but armv8 instead of armv7.

https://buildbot.python.org/#/builders/424/builds/9978/steps/3/logs/stdio

[vfazio]

Fantastic, thanks