Build failure on AArch64 Ubuntu 20.04

[sparker-arm]

Hi,

I've just updated the LLVM submodule, from 14 to 15, and now the wasi-sdk build is failing. It looks like it's trying to build something very much x86 specific:

lib/Support/BLAKE3/CMakeFiles/LLVMSupportBlake3.dir/blake3_avx512_x86-64_unix.S.o
/usr/bin/cc -DGTEST_HAS_RTTI=0 -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -Ilib/Support/BLAKE3 -I~/src/WebAssembly/wasi-sdk/src/llvm-project/llvm/lib/Support/BLAKE3 -Iinclude -I~/src/WebAssembly/wasi-sdk/src/llvm-project/llvm/include -fPIC -Os -DNDEBUG -mavx512vl -MD -MT lib/Support/BLAKE3/CMakeFiles/LLVMSupportBlake3.dir/blake3_avx512_x86-64_unix.S.o -MF lib/Support/BLAKE3/CMakeFiles/LLVMSupportBlake3.dir/blake3_avx512_x86-64_unix.S.o.d -o lib/Support/BLAKE3/CMakeFiles/LLVMSupportBlake3.dir/blake3_avx512_x86-64_unix.S.o -c ~/src/WebAssembly/wasi-sdk/src/llvm-project/llvm/lib/Support/BLAKE3/blake3_avx512_x86-64_unix.S
cc: error: unrecognized command line option ‘-mavx512vl’

[sbc100]

What is the compiler you are using to build llvm? (i.e. what does /usr/bin/cc --version say?

[sbc100]

FWIW, the flag looks like its coming from here: https://github.com/llvm/llvm-project/blob/079c488c66056f7bf22c30ee280489f6c43b7658/llvm/lib/Support/BLAKE3/CMakeLists.txt#L69-L71

[sparker-arm]

Ah, sorry!

$ cc --version
cc (Ubuntu 9.4.0-1ubuntu1~20.04.1) 9.4.0

I'm just using all the defaults, and calling make build.

[sbc100]

This looks like some kind of llvm configuration issue. The whole block that adds -mavx512vl and blake3_avx512_x86-64_unix.S should be x86_64 only. If you are building with an arm64 version of gcc I don't think those should even be included.

[sparker-arm]

Indeed. I went through the CMake config and the only thing that looked suspicious was the OSX settings here. Removing this line fixes the issue, but unfortunately I'm not in the position to create a PR.

[sbc100]

That interesting. Seems like a bug in the llvm build system that -DCMAKE_OSX_ARCHITECTURES does anything at all when building on linux.

I guess we can work around it downstream by finding a way to only pass this argument when actual running on macOS.

[TerrorJack]

I can build on aarch64 alpine linux and -DCMAKE_OSX_ARCHITECTURES don't seem to be a problem: https://gitlab.haskell.org/ghc/wasi-sdk/-/jobs/1361963

[gzurl]

I can confirm that removing the -DCMAKE_OSX_ARCHITECTURES line from Makefile (as pointed by @sparker-arm) solves the issue on Ubuntu 22.04 arm64.

[sbc100]

I wonder if this is maybe something that was fixed upstream in llvm, or should be? Could somebody confirm if this issue also occurs with llvm main?

[sparker-arm]

I was going to say that I've never had a problem building LLVM on my system, but then I remembered that I use clang :)

But double-checking with the default system toolchain (ubuntu gcc-9.4.0), I have no problems building 15.0.7 and main.

Building LLVM doesn't set CMAKE_OSX_ARCHITECTURES, at least not on Linux. I guess we just need to check IS_X64 here, but I'm wondering how this works on MacOS, is -mavx512vl a clang only option? @TerrorJack you're using clang as a compiler, right?

[johalun]

I got this error and another compile error later on when using GCC. No issues at all when using clang.

This in aarch64 Ubuntu VM on Apple Silicon.

[matsbror]

I think this is handled by PR #321