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[BUG] cross compiling 3.15 abi3 wheels fails due to new multiarch support #5351

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[BUG] cross compiling 3.15 abi3 wheels fails due to new multiarch support#5351
#5352
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Needs TriageIssues that need to be evaluated for severity and status.bug

Description

@vfazio
vfazio
opened on Oct 16, 2026

setuptools version

80.9.0

Python version

Python 3.15

OS

Linux (Buildroot)

Additional environment information

This is in buildroot builds which is slightly complicated but we can get into that if necessary

Description

When building the https://github.com/pyca/pynacl package in buildroot, we may have to cross compile for a foreign architecture.

when doing so, we use host python but feed a lot of environment information to denote the cross environment:

>>> python-pynacl 1.6.2 Extracting
gzip -d -c /home/vfazio/development/buildroot/dl/python-pynacl/pynacl-1.6.2.tar.gz | tar --strip-components=1 -C /home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/build/python-pynacl-1.6.2   -xf -
>>> python-pynacl 1.6.2 Patching
>>> python-pynacl 1.6.2 Configuring
>>> python-pynacl 1.6.2 Building
(cd /home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/build/python-pynacl-1.6.2//; _PYTHON_HOST_PLATFORM="linux-arm" _PYTHON_PROJECT_BASE="/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/build/python3-3.15.0" _PYTHON_SYSCONFIGDATA_NAME="`{ [ -e /home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/arm-buildroot-linux-musleabi/sysroot/usr/lib/python3.15//_sysconfigdata__linux_*.py ] && basename /home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/arm-buildroot-linux-musleabi/sysroot/usr/lib/python3.15//_sysconfigdata__linux_*.py .py; } || true`" PATH="/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/bin:/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/sbin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin" GIT_DIR=. PATH="/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/bin:/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/sbin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin" AR="/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/bin/arm-linux-gcc-ar" AS="/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/bin/arm-linux-as" LD="/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/bin/arm-linux-ld" NM="/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/bin/arm-linux-gcc-nm" CC="/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/bin/arm-linux-gcc" GCC="/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/bin/arm-linux-gcc" CPP="/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/bin/arm-linux-cpp" CXX="/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/bin/arm-linux-g++" FC="/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/bin/arm-linux-gfortran" F77="/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/bin/arm-linux-gfortran" RANLIB="/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/bin/arm-linux-gcc-ranlib" READELF="/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/bin/arm-linux-readelf" STRIP="/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/bin/arm-linux-strip" OBJCOPY="/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/bin/arm-linux-objcopy" OBJDUMP="/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/bin/arm-linux-objdump" AR_FOR_BUILD="/usr/bin/ar" AS_FOR_BUILD="/usr/bin/as" CC_FOR_BUILD="/usr/bin/gcc" GCC_FOR_BUILD="/usr/bin/gcc" CXX_FOR_BUILD="/usr/bin/g++" LD_FOR_BUILD="/usr/bin/ld" CPPFLAGS_FOR_BUILD="-I/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/include" CFLAGS_FOR_BUILD="-O2 -I/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/include" CXXFLAGS_FOR_BUILD="-O2 -I/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/include" LDFLAGS_FOR_BUILD="-L/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/lib -Wl,-rpath,/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/lib" FCFLAGS_FOR_BUILD="" DEFAULT_ASSEMBLER="/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/bin/arm-linux-as" DEFAULT_LINKER="/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/bin/arm-linux-ld" CPPFLAGS="-D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64" CFLAGS="-D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64  -O2 -g0 " CXXFLAGS="-D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64  -O2 -g0 " LDFLAGS="" FCFLAGS=" -O2 -g0" FFLAGS=" -O2 -g0" PKG_CONFIG="/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/bin/pkg-config" STAGING_DIR="/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/arm-buildroot-linux-musleabi/sysroot" INTLTOOL_PERL=/usr/bin/perl PYTHONPATH="/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/arm-buildroot-linux-musleabi/sysroot/usr/lib/python3.15/" PYTHONNOUSERSITE=1 SODIUM_INSTALL=system /home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/bin/python3 -m build -n -w )

When the build_ext phase runs, we see this:

running build_ext
generating cffi module 'build/temp.linux-arm-cpython-315/_sodium.c'
creating build/temp.linux-arm-cpython-315
building '_sodium' extension
creating build/temp.linux-arm-cpython-315/build/temp.linux-arm-cpython-315
/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/bin/arm-linux-gcc -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -O2 -g0 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -fPIC -I/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/build/python3-3.15.0/Include -I/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/build/python3-3.15.0 -c build/temp.linux-arm-cpython-315/_sodium.c -o build/temp.linux-arm-cpython-315/build/temp.linux-arm-cpython-315/_sodium.o
/home/vfazio/development/buildroot/output/TestPythonPy3Pynacl/host/bin/arm-linux-gcc -shared -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -O2 -g0 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 build/temp.linux-arm-cpython-315/build/temp.linux-arm-cpython-315/_sodium.o -L. -lsodium -o build/lib.linux-arm-cpython-315/nacl/_sodium.abi3-x86_64-linux-gnu.so
installing to build/bdist.linux-arm/wheel
running install

While the compiler invoked is correct (arm) the generated library has the wrong architecture (x86_64).

I think this is due to https://github.com/pypa/setuptools/blob/main/setuptools/command/build_ext.py#L79

this line is looking for .abi3 but after python/cpython#152461 landed, the multiarch abi3 entry is enumerated first:

>>> import importlib.machinery
>>> importlib.machinery.EXTENSION_SUFFIXES
['.cpython-315-x86_64-linux-gnu.so', '.abi3-x86_64-linux-gnu.so', '.abi3.so', '.abi3t-x86_64-linux-gnu.so', '.abi3t.so', '.so']

This was backported to 3.15: python/cpython#154772

So this function now returns an incompatible string for the name of the shared/static library that gets generated.

Expected behavior

The target architecture should be specified in the generated shared library or it should be agnostic and not specify the multiarch name.

How to Reproduce

clone buildroot

I'm tracking some of this migration in https://gitlab.com/buildroot.org/buildroot/-/work_items/193

Output

Activity
  1. vfazio
    added 
    bug
     
    Needs TriageIssues that need to be evaluated for severity and status.
     on Oct 16, 2026
  2. vfazio commented on Oct 16, 2026 
    @vfazio
    vfazio
    on Oct 16, 2026
    ContributorAuthor
    @jaraco FYI
  3. vfazio commented on Oct 16, 2026 
    @vfazio
    vfazio
    on Oct 16, 2026
    ContributorAuthor
    I guess if we fix logic around this, there may also be considerations for abi3t
  4. vfazio commented on Oct 16, 2026 
    @vfazio
    vfazio
    on Oct 16, 2026
    ContributorAuthor
    dynload_shlib::_PyImport_DynLoadFiletab defines these values.
    

    Changing the pattern to .abi3. fixes my immediate problem but has the downside of not allowing multiarch wheels to be generated.
  5. jameshilliard
    added a commit that references this issue on Oct 16, 2026
    Use target sysconfig for platform-qualified stable-ABI suffixes
    dfd04e8
  6. jameshilliard commented on Oct 16, 2026 
    @jameshilliard
    jameshilliard
    on Oct 16, 2026
    Contributor
    I think something like #5352 should fix this properly.
  7. jameshilliard
    added 3 commits that reference this issue on Oct 16, 2026
    Use target sysconfig for platform-qualified stable-ABI suffixes
    3c3a334
    Use target sysconfig for platform-qualified stable-ABI suffixes
    28b1988
    Use target sysconfig for platform-qualified stable-ABI suffixes
    97b75e6
  8. jaraco
    closed this as completedin #5352on Oct 19, 2026
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