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

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Message-ID: <CAEf4BzbHQ6WajDTAWHmjvA2FaAQz37sd8RwFY9ysKK7D+uc_=A@mail.gmail.com>
Date: Wed, 5 Feb 2025 16:50:52 -0800
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Daniel Xu <dxu@...uu.xyz>
Cc: shuah@...nel.org, andrii@...nel.org, eddyz87@...il.com, ast@...nel.org, 
	nathan@...nel.org, daniel@...earbox.net, martin.lau@...ux.dev, 
	song@...nel.org, yonghong.song@...ux.dev, john.fastabend@...il.com, 
	kpsingh@...nel.org, sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org, 
	mykolal@...com, ndesaulniers@...gle.com, morbo@...gle.com, 
	justinstitt@...gle.com, bpf@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] selftests: bpf: Support dynamic linking LLVM if static
 not available

On Thu, Jan 30, 2025 at 2:34 PM Daniel Xu <dxu@...uu.xyz> 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@...uu.xyz>
> ---
>  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
>