Re: [PATCH] selftests: bpf: Support dynamic linking LLVM if static not available

[Andrii Nakryiko]

On Thu, Jan 30, 2025 at 2:34 PM Daniel Xu <dxu@xxxxxxxxx> wrote:
>
> Since 67ab80a01886 ("selftests/bpf: Prefer static linking for LLVM
> libraries"), only statically linking test_progs is supported. However,
> some distros only provide a dynamically linkable LLVM.
>
> This commit adds a fallback for dynamically linking LLVM if static
> linking is not available. If both options are available, static linking
> is chosen.
>
> Signed-off-by: Daniel Xu <dxu@xxxxxxxxx>
> ---
>  tools/testing/selftests/bpf/Makefile | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
>

Note, we expect [PATCH bpf-next] as subject prefix and "selftests/bpf:
" prefix for BPF selftest-related patches. Please help with
consistency. I fixed it up while applying.

> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index 6722080b2107..da514030a153 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -184,9 +184,14 @@ ifeq ($(feature-llvm),1)
>    LLVM_CONFIG_LIB_COMPONENTS := mcdisassembler all-targets
>    # both llvm-config and lib.mk add -D_GNU_SOURCE, which ends up as conflict
>    LLVM_CFLAGS  += $(filter-out -D_GNU_SOURCE,$(shell $(LLVM_CONFIG) --cflags))
> -  LLVM_LDLIBS  += $(shell $(LLVM_CONFIG) --link-static --libs $(LLVM_CONFIG_LIB_COMPONENTS))
> -  LLVM_LDLIBS  += $(shell $(LLVM_CONFIG) --link-static --system-libs $(LLVM_CONFIG_LIB_COMPONENTS))
> -  LLVM_LDLIBS  += -lstdc++
> +  # Prefer linking statically if it's available, otherwise fallback to shared
> +  ifeq ($(shell $(LLVM_CONFIG) --link-static --libs &> /dev/null && echo static),static)
> +    LLVM_LDLIBS  += $(shell $(LLVM_CONFIG) --link-static --libs $(LLVM_CONFIG_LIB_COMPONENTS))
> +    LLVM_LDLIBS  += $(shell $(LLVM_CONFIG) --link-static --system-libs $(LLVM_CONFIG_LIB_COMPONENTS))
> +    LLVM_LDLIBS  += -lstdc++
> +  else
> +    LLVM_LDLIBS  += $(shell $(LLVM_CONFIG) --link-shared --libs $(LLVM_CONFIG_LIB_COMPONENTS))
> +  endif
>    LLVM_LDFLAGS += $(shell $(LLVM_CONFIG) --ldflags)
>  endif
>
> --
> 2.47.1
>