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

[Paul Chaignon <paul.chaignon@gmail.com>]

On Thu, May 14, 2026 at 04:23:04AM +0000, sashiko-bot@kernel.org wrote:
> 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.
> --
> 
> 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.

I'm not sure I'm following this, but I have static LLVM libraries with
llvm-config --shared-mode set to "shared" and everything seems to build
fine.

> 
> Additionally, if static LLVM libraries are entirely absent, the feature test
> fails, causing bpftool to silently build without LLVM support.
> 
> -- 
> Sashiko AI review · https://sashiko.dev/#/patchset/714556da329c812988010ffe53173d9152570a78.1778669303.git.paul.chaignon@gmail.com?part=1