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

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

[Paul Chaignon]

When running vmtest.sh with static linking, the bpftool_map_access
selftests fail. These selftests are calling the bpftool binary in
tools/sbin/ directly, which results in the following error:

    error while loading shared libraries: libLLVM.so.21.1:
      cannot open shared object file: No such file or directory

To fix this, we need to also build bpftool statically. That can be done
by setting EXTRA_LDFLAGS=-static.

Fixes: 2d96bbdfd3b5 ("selftests/bpf: convert test_bpftool_map_access.sh into test_progs framework")
Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
---
 tools/testing/selftests/bpf/README.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/README.rst b/tools/testing/selftests/bpf/README.rst
index 776fbe3cb8f9..37164322a102 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
 
 .. note:: Some distros may not support static linking.
 
-- 
2.43.0

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

[Jakub Sitnicki]

On Wed, May 13, 2026 at 01:24:37PM +0200, Paul Chaignon wrote:
> When running vmtest.sh with static linking, the bpftool_map_access
> selftests fail. These selftests are calling the bpftool binary in
> tools/sbin/ directly, which results in the following error:
> 
>     error while loading shared libraries: libLLVM.so.21.1:
>       cannot open shared object file: No such file or directory
> 
> To fix this, we need to also build bpftool statically. That can be done
> by setting EXTRA_LDFLAGS=-static.
> 
> Fixes: 2d96bbdfd3b5 ("selftests/bpf: convert test_bpftool_map_access.sh into test_progs framework")
> Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
> ---

That seems to do the trick.

Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>

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

[sashiko-bot]

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.

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

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

[Paul Chaignon]

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

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

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Alexei Starovoitov <ast@kernel.org>:

On Wed, 13 May 2026 13:24:37 +0200 you wrote:
> When running vmtest.sh with static linking, the bpftool_map_access
> selftests fail. These selftests are calling the bpftool binary in
> tools/sbin/ directly, which results in the following error:
> 
>     error while loading shared libraries: libLLVM.so.21.1:
>       cannot open shared object file: No such file or directory
> 
> [...]

Here is the summary with links:
  - [bpf-next] selftests/bpf: Override EXTRA_LDFLAGS for static builds
    https://git.kernel.org/bpf/bpf-next/c/879daba303f7

You are awesome, thank you!
-- 
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