pkgconfig returns `-fopenmp` option

[vabenil]

The pkgconfig for openblas returns the -fopenmp flag for library. So that when pkg-config is run like so:

$ pkg-config --libs openblas

The returned output is: -fopenmp -lopenblas.

This should be considered as an error because -fopenmp is not a linking flag (Not something you would pass to ld). The -fopenmp flag should be returned by pkg-config --cflags instead, since -fopenmp is a C specific option.

I came across this problem when compiling a D project using dub with the openblas library. There dub tries to use pkg-config to figure out linking flags, tries to add -fopenmp which then causes an error because -fopenmpis not a linking flag and has no meaning in D.

This issue was downstreamed from https://gitlab.archlinux.org/archlinux/packaging/packages/openblas/-/issues/10.

[isuruf]

Don't you need -fopenmp sent to the compiler in the linking phase in order for the binary to link to libgomp/libomp?

[martin-frbg]

I'm led to believe the link line needs to be parsable by ld, also this line will have the appropriate -l option for linking the openmp library as well.

[vabenil]

@isuruf As far as I understand the only things that are considered linking flags are flags with -l as @martin-frbg mentioned. The gcc docs also mention that -fopenmp is a option and it's C dependent, which as in my case in D causes problems when requesting linking flags (that should work independent of language) and receiving a C option flag instead.