blas build: use configuration from pkg_check_modules(DepBLAS openblas) and alike

[khumarahn]

Hi. On my system (a gentoo), cmake build process with OpenBLAS or BLIS fails because linker options like -openblas or -lblis are missing.

With BLIS:

$ cmake -B build -DGGML_BLAS=ON -DGGML_BLAS_VENDOR=FLAME -DBUILD_NUMBER=1 && cmake --build build --config Release -v
...
[ 26%] Linking CXX executable ../bin/test-tokenizer-0
cd llama.cpp/build/tests && /usr/bin/cmake -E cmake_link_script CMakeFiles/test-tokenizer-0.dir/link.txt --verbose=1
/usr/bin/c++ -O3 -DNDEBUG "CMakeFiles/test-tokenizer-0.dir/test-tokenizer-0.cpp.o" -o ../bin/test-tokenizer-0  -Wl,-rpath,llama.cpp/build/bin: ../common/libcommon.a ../bin/libllama.so ../bin/libggml.so ../bin/libggml-cpu.so ../bin/libggml-blas.so ../bin/libggml-base.so
/usr/lib/gcc/x86_64-pc-linux-gnu/14/../../../../x86_64-pc-linux-gnu/bin/ld: ../bin/libggml-blas.so: undefined reference to `bli_thread_set_num_threads'
/usr/lib/gcc/x86_64-pc-linux-gnu/14/../../../../x86_64-pc-linux-gnu/bin/ld: ../bin/libggml-blas.so: undefined reference to `cblas_sgemm'
collect2: error: ld returned 1 exit status
gmake[2]: *** [tests/CMakeFiles/test-tokenizer-0.dir/build.make:103: bin/test-tokenizer-0] Error 1
gmake[2]: Leaving directory 'llama.cpp/build'
gmake[1]: *** [CMakeFiles/Makefile2:1906: tests/CMakeFiles/test-tokenizer-0.dir/all] Error 2
gmake[1]: Leaving directory 'llama.cpp/build'
gmake: *** [Makefile:146: all] Error 2

or with OpenBLAS:

$ cmake -B build -DGGML_BLAS=ON -DGGML_BLAS_VENDOR=OpenBLAS -DBUILD_NUMBER=1 && cmake --build build --config Release -v
[ 26%] Linking CXX executable ../bin/test-tokenizer-0
cd llama.cpp/build/tests && /usr/bin/cmake -E cmake_link_script CMakeFiles/test-tokenizer-0.dir/link.txt --verbose=1
/usr/bin/c++ -O3 -DNDEBUG "CMakeFiles/test-tokenizer-0.dir/test-tokenizer-0.cpp.o" -o ../bin/test-tokenizer-0  -Wl,-rpath,llama.cpp/build/bin: ../common/libcommon.a ../bin/libllama.so ../bin/libggml.so ../bin/libggml-cpu.so ../bin/libggml-blas.so ../bin/libggml-base.so
/usr/lib/gcc/x86_64-pc-linux-gnu/14/../../../../x86_64-pc-linux-gnu/bin/ld: ../bin/libggml-blas.so: undefined reference to `openblas_set_num_threads'
/usr/lib/gcc/x86_64-pc-linux-gnu/14/../../../../x86_64-pc-linux-gnu/bin/ld: ../bin/libggml-blas.so: undefined reference to `cblas_sgemm'
collect2: error: ld returned 1 exit status
gmake[2]: *** [tests/CMakeFiles/test-tokenizer-0.dir/build.make:103: bin/test-tokenizer-0] Error 1
gmake[2]: Leaving directory 'llama.cpp/build'
gmake[1]: *** [CMakeFiles/Makefile2:1906: tests/CMakeFiles/test-tokenizer-0.dir/all] Error 2
gmake[1]: Leaving directory 'llama.cpp/build'
gmake: *** [Makefile:146: all] Error 2

The problem seems to be quite basic: the build process is not using DepBLAS_LIBRARIES and DepBLAS_LINKER_FLAGS that come from pkg_check_modules(DepBLAS openblas) or similar. So I added a couple of lines to fix it. I'm not sure that this is the right fix, and I don't know cmake, but it seems sensible.

P.S.: Edited because at first I was wrong
P.P.S.: Added the error output so people who have the same problem are more likely to find it

[slaren]

BLAS_LIBRARIES and BLAS_LINKER_FLAGS should already be set by https://cmake.org/cmake/help/latest/module/FindBLAS.html. I believe pkgconfig is used only to find the include directories, since that's something that FindBLAS does not do.

[khumarahn]

It makes sense, but I'm not sure why that isn't working. FindBLAS is pointing me to /usr/lib64/libblas.so which is installed by lapack, neither blis nor openblas.

A slightly modified cmake script to print out the variables gives:

-- BLAS found:
--     Libraries: /usr/lib64/libblas.so
--     Include dirs: 
--     Linker flags: 
-- Found PkgConfig: /usr/bin/pkg-config (found version "2.3.0")
-- Checking for module 'openblas64'
--   Package 'openblas64' not found
-- Checking for module 'openblas'
--   Found openblas, version 0.3.29
-- DepBLAS found:
--     Libraries: openblas
--     Include dirs: /usr/include/openblas
--     Linker flags: 

[khumarahn]

I think I understand this better now. But I'm lost even more.

To the best of my current understanding, this issue is a combination of two problems:

• if BLA_PREFER_PKGCONFIG is set, then cmake is looking for blas with pkgconfig without taking into account BLA_VENDOR
  https://github.com/Kitware/CMake/blob/6a3631207a768e5b8c6b7446763a2085dfb8fdf1/Modules/FindBLAS.cmake#L291
  This can be considered as broken, but it is not normally happening because BLA_PREFER_PKGCONFIG in llama.cpp is not set.
• But Gentoo patches cmake, adding set(BLA_PREFER_PKGCONFIG ON) in the beginning of FindBLAS.cmake.
  https://gitweb.gentoo.org/repo/gentoo.git/tree/dev-build/cmake/files/cmake-3.27.0_rc1-0003-Prefer-pkgconfig-in-FindBLAS.patch
  This looks innocent and would work if not for the previous point...

UPD: an old bug in gentoo: https://bugs.gentoo.org/736547

[slaren]

On Ubuntu 24.04, it works as it is for both OpenBLAS and BLIS. Maybe we can add a workaround for distributions where FindBLAS is broken, but it should be optional.