78 lines
4.0 KiB
Markdown
78 lines
4.0 KiB
Markdown
This page describes how to natively build OpenBLAS library for windows on arm64 targets.
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See [below](#xcomp) for how to cross-compile OpenBLAS for WoA on an x86_64 Windows host.
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_We hope that the procedure can be simplified for/by LLVM 17+ and its flang-new compiler for the FORTRAN parts (LAPACK) of the code but we have no means of verifying that as of January 2024._
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# Prerequisite
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Following tools needs to be installed
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## 1. Download and install clang for windows on arm
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Find the latest LLVM build for WoA from [LLVM release page](https://releases.llvm.org/)
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E.g: LLVM 12 build for WoA64 can be found [here](https://github.com/llvm/llvm-project/releases/download/llvmorg-12.0.0/LLVM-12.0.0-woa64.exe)
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Run the LLVM installer and ensure that LLVM is added to environment PATH.
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## 2. Download and install classic flang for windows on arm
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Classic flang is the only available FORTRAN compiler for windows on arm for now and a pre-release build can be found [here](https://github.com/kaadam/flang/releases/tag/v0.1)
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There is no installer for classic flang and the zip package can be extracted and the path needs to be added to environment PATH.
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E.g: on PowerShell
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`$env:Path += ";C:\flang_woa\bin"`
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# Build
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The following steps describe how to build the static library for OpenBLAS with and without LAPACK
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## 1. Build OpenBLAS static library with BLAS and LAPACK routines with Make
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Following command can be used to build OpenBLAS static library with BLAS and LAPACK routines
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`make CC="clang-cl" HOSTCC="clang-cl" AR="llvm-ar" BUILD_WITHOUT_LAPACK=0 NOFORTRAN=0 DYNAMIC_ARCH=0 TARGET=ARMV8 ARCH=arm64 BINARY=64 USE_OPENMP=0 PARALLEL=1 RANLIB="llvm-ranlib" MAKE=make F_COMPILER=FLANG FC=FLANG FFLAGS_NOOPT="-march=armv8-a -cpp" FFLAGS="-march=armv8-a -cpp" NEED_PIC=0 HOSTARCH=arm64 libs netlib`
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## 2. Build static library with BLAS routines using CMake
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Classic flang has compatibility issues with cmake hence only BLAS routines can be compiled with CMake
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`mkdir build`
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`cd build`
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`cmake .. -G Ninja -DCMAKE_C_COMPILER=clang -DBUILD_WITHOUT_LAPACK=1 -DNOFORTRAN=1 -DDYNAMIC_ARCH=0 -DTARGET=ARMV8 -DARCH=arm64 -DBINARY=64 -DUSE_OPENMP=0 -DCMAKE_SYSTEM_PROCESSOR=ARM64 -DCMAKE_CROSSCOMPILING=1 -DCMAKE_SYSTEM_NAME=Windows`
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`cmake --build . --config Release`
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# Known issue
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## `getarch.exe` execution error
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If you notice that platform-specific headers by `getarch.exe` are not generated correctly, It could be due to a known debug runtime DLL issue for arm64 platforms. Please check out [link](https://linaro.atlassian.net/wiki/spaces/WOAR/pages/28677636097/Debug+run-time+DLL+issue#Workaround) for the workaround.
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# <a id="xcomp"></a>Alternative: cross-compiling on Windows x86
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## Prerequisites:
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a working installation of LLVM and Ninja (the versions included in the latest Visual Studio 2022 will do, if you install its optional Llvm.Clang component)
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## Build
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1. Load into the appropriate cross compiling developer shell (in this case powershell, for cmd.exe it would be vcvarsamd64_arm64.bat):
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'C:\Program Files\Microsoft Visual Studio\2022\Professional\Common7\Tools\Launch-VsDevShell.ps1' -Arch arm64 -HostArch amd64
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2. Change to the folder where you unpacked the OpenBLAS sources if you haven't already, and create a subfolder for building.
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Then change into that folder.
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3. Invoke the following CMake command
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```
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cmake .. -G Ninja -DCMAKE_BUILD_TYPE=Release -DTARGET=ARMV8 -DCMAKE_CROSSCOMPILING=ON -DCMAKE_SYSTEM_NAME="Windows" -DARCH=arm -DBINARY=64 -DCMAKE_SYSTEM_PROCESSOR=ARM64 -DCMAKE_C_COMPILER=clang-cl -DCMAKE_C_COMPILER_TARGET=arm64-pc-windows-msvc -DCMAKE_ASM_COMPILER_TARGET=arm64-pc-windows-msvc.
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```
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(Note the use of clang-cl instead of clang, and adding in the _COMPILER_TARGET entries. Without C_COMPILER_TARGET, clang-cl will be trying to compile x64 machine code and not make it past the cmake generation step. Without ASM_COMPILER_TARGET the assembly files in openblas will fail to assemble because the assembler is trying to interpret them as x64 assembly.)
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4. Invoke Ninja for the actual compilation
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