Re: [PATCH bpf-next] selftests/bpf: Override EXTRA_LDFLAGS for static builds

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The suggested workaround `EXTRA_LDFLAGS=-static` in README.rst breaks the bpftool build or silently disables LLVM support.
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commit dcbd0d5d7a0eb4a9300ad0890d83b7e4cdfd3aeb
Author: Paul Chaignon <paul.chaignon@gmail.com>

selftests/bpf: Override EXTRA_LDFLAGS for static builds

This commit updates the README.rst for BPF selftests to include
EXTRA_LDFLAGS=-static when recommending how to statically link,
in order to fix shared library loading errors with libLLVM.so
when running vmtest.sh.

> diff --git a/tools/testing/selftests/bpf/README.rst b/tools/testing/selftests/bpf/README.rst
> index 776fbe3cb8f9b..37164322a1023 100644
> --- a/tools/testing/selftests/bpf/README.rst
> +++ b/tools/testing/selftests/bpf/README.rst
> @@ -77,7 +77,7 @@ In case of linker errors when running selftests, try using static linking:
>  
>  .. code-block:: console
>  
> -  $ LDLIBS=-static PKG_CONFIG='pkg-config --static' vmtest.sh
> +  $ LDLIBS=-static EXTRA_LDFLAGS=-static PKG_CONFIG='pkg-config --static' vmtest.sh

Can adding EXTRA_LDFLAGS=-static break the bpftool build or silently disable
LLVM support?

In the bpftool Makefile, LLVM's --system-libs and -lstdc++ are only appended
to LIBS if llvm-config --shared-mode outputs 'static'. However, the
feature-llvm test in tools/build/feature/Makefile unconditionally includes
--system-libs and uses g++, which automatically includes -lstdc++.

If a system has static LLVM libraries but llvm-config --shared-mode is set
to 'shared' (common on many distros), the feature-llvm test statically links
successfully, but bpftool's Makefile will attempt to build with LLVM support
using gcc -static while omitting --system-libs and -lstdc++. This can cause
the build to fail with undefined references.

Additionally, if static LLVM libraries are entirely absent, the feature test
fails, causing bpftool to silently build without LLVM support.

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Sashiko AI review · https://sashiko.dev/#/patchset/714556da329c812988010ffe53173d9152570a78.1778669303.git.paul.chaignon@gmail.com?part=1