Re: [PATCH bpf-next v9 09/11] selftests/bpf: Tolerate benchmark build failures

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [Medium] Skipped `bench` binary causes `make install` to fail due to missing files in `TEST_GEN_PROGS_EXTENDED`.
- [Medium] Using `$(wildcard $^)` to filter missing prerequisites breaks `make -n` (dry run) and drastically increases compiler error noise.
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commit 31a306fe854d559a436ecf84354b5b73a31012e8
Author: Ricardo B. Marlière <rbm@suse.com>

selftests/bpf: Tolerate benchmark build failures

This commit modifies the selftests/bpf Makefile to tolerate build failures
for benchmark objects when PERMISSIVE is set. It changes the compilation and
linking steps for the bench binary to emit a skip message and avoid failing
the entire build if a dependency is missing or fails to compile.

> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index a64e822dc540..db4ff951fc88 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile

[ ... ]

> @@ -988,7 +989,8 @@ $(OUTPUT)/bench: $(OUTPUT)/bench.o \
>  		 $(OUTPUT)/usdt_2.o \
>  		 #
>  	$(call msg,BINARY,,$@)
> -	$(Q)$(CC) $(CFLAGS) $(LDFLAGS) $(filter %.a %.o,$^) $(LDLIBS) -o $@
> +	$(Q)$(CC) $(CFLAGS) $(LDFLAGS) $(filter %.a %.o,$(if $(PERMISSIVE),$(wildcard $^),$^)) $(LDLIBS) -o $@ $(if $(PERMISSIVE),|| \
> +		($(RM) $@; printf '  %-12s %s\n' 'SKIP-LINK' '$(notdir $@) (some benchmarks may have been skipped)' 1>&2))

Does using $(wildcard $^) here break make -n (dry run) and cause excessive
linker noise?

Since bench.c statically references every benchmark, omitting missing objects
from the command line forces the linker to run anyway, resulting in a large
number of undefined reference errors before it fails.

If $^ were used directly, the compiler would fail cleanly and immediately with
a "No such file or directory" error before running the linker, which would
then correctly trigger the || SKIP-LINK fallback.

Also, evaluating $(wildcard $^) in a recipe causes missing generated objects
to be silently omitted during make -n.

Will skipping the bench binary cleanly cause make install to fail, since
bench is unconditionally listed in TEST_GEN_PROGS_EXTENDED?

During make install, the selftest build system uses rsync to copy all targets
in TEST_GEN_PROGS_EXTENDED. Since the skipped bench binary won't exist on disk,
rsync fails with a "No such file or directory" error and aborts the pipeline,
defeating the purpose of the permissive build mode.

I do see this was fixed later in the series by commit
ce682ab9bce04cbe3adda3d7a63647774ad61f5d "selftests/bpf: Tolerate missing
files during install".

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Sashiko AI review · https://sashiko.dev/#/patchset/20260429-selftests-bpf_misconfig-v9-0-c311f06b4791@suse.com?part=9