custom_ops fails to build when cross-compiling to x64 from arm64

[zcbenz]

🐛 Describe the bug

Run following command to build for x64 on arm64 mac:

cmake . -B out \
-DCMAKE_BUILD_TYPE=Release \
-DCMAKE_PREFIX_PATH=/opt/homebrew/Caskroom/miniconda/base/envs/executorch/lib/python3.10/site-packages/torch \
-DPYTHON_EXECUTABLE=/opt/homebrew/Caskroom/miniconda/base/envs/executorch/bin/python3 \
-DFLATC_EXECUTABLE=/opt/homebrew/Caskroom/miniconda/base/envs/executorch/bin/flatc \
-DEXECUTORCH_BUILD_EXTENSION_DATA_LOADER=ON \
-DEXECUTORCH_BUILD_EXTENSION_MODULE=ON \
-DEXECUTORCH_BUILD_EXTENSION_TENSOR=ON \
-DEXECUTORCH_BUILD_KERNELS_CUSTOM=ON \
-DEXECUTORCH_BUILD_KERNELS_OPTIMIZED=ON \
-DEXECUTORCH_BUILD_KERNELS_QUANTIZED=ON \
-DEXECUTORCH_BUILD_XNNPACK=ON \
-DDEPLOYMENT_TARGET=10.15 \
-DEXECUTORCH_BUILD_COREML=ON \
-DEXECUTORCH_BUILD_MPS=ON \
-DCMAKE_TOOLCHAIN_FILE=third-party/ios-cmake/ios.toolchain.cmake \
-DPLATFORM=MAC
cmake --build out --config Release -j 

And compilation fails at custom_ops:

/Users/zcbenz/codes/executorch-binaries/executorch/extension/llm/custom_ops/spinquant/third-party/FFHT/fht_neon.c:28:11: error: unknown register name '%v0' in asm
 : "%v0",
 ^
/Users/zcbenz/codes/executorch-binaries/executorch/extension/llm/custom_ops/spinquant/third-party/FFHT/fht_neon.c:82:15: error: unknown register name '%v0' in asm
 : "%v0",
 ^

Which is because of fht_neon.c being compiled for x64.

The extension/llm/custom_ops/spinquant/third-party/FFHT/targets.bzl file sets the file to only build from arm64, so I suspect the build system did not handle target/host arch correctly somewhere, however I know nothing about buck2 so I can't see how to fix this, even though I suspect the fix could be simple.

Also note that while mac x64 is not a supported target, everything else works fine with EXECUTORCH_BUILD_KERNELS_CUSTOM=OFF.

Versions

I'm building with the latest ExecuTorch (5b51bb8).

cc @larryliu0820

[GregoryComer]

Looks like the same root cause as #6691. There is an outstanding PR to resolve platform-related build issues with spinquant here: #6731 Once that lands, I'm hopeful that will resolve this issue.

[larryliu0820]

@zcbenz can you try patching #6731 and see if it fixes your issue?

[zcbenz]

No I tried #6731 and it did not fix this, I think it fixes arm64 target on x64 host, while this issue is x64 target on arm64 host.

[jathu]

@zcbenz seems like this was fixed in #8346, can please verify it?

[zcbenz]

Thanks!