Re: [RFC PATCH bpf-next v2 3/3] selftests/bpf: build each test runner instance in its own sub-make

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] In permissive mode, test objects are treated exclusively as order-only prerequisites, which completely breaks incremental test development by never relinking the test runner when test sources are modified.
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--- Patch [3]: [RFC PATCH bpf-next v2 3/3] selftests/bpf: build each test runner instance in its own sub-make ---
commit f7cbf6f3b146270d8f7ba71d9ea0557ab2070208
Author: Mykola Lysenko <nickolay.lysenko@gmail.com>

selftests/bpf: build each test runner instance in its own sub-make

This commit refactors the bpf selftests build system to use a dedicated
Makefile.runner for each test runner instance, running them in separate
sub-makes. It aims to eliminate double-expansion complexity while fixing
parallel build races.

> diff --git a/tools/testing/selftests/bpf/Makefile.runner b/tools/testing/selftests/bpf/Makefile.runner
> new file mode 100644
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/Makefile.runner

[ ... ]

> +# In permissive mode, link whatever test objects were successfully built
> +# (their compilation may have been skipped); the wildcard in the recipe
> +# picks up the survivors at link time.
> +# Prerequisite order is also link order (test objects, extra objects,
> +# libbpf, lib objects).
> +$(OUTPUT)/$(BINARY): $(if $(PERMISSIVE_TESTS),,$(TEST_OBJS))		\
> +		     $(EXTRA_OBJS) $(BPFOBJ) $(LIB_OBJS)		\
> +		     $(TRUNNER_BPFTOOL) $(OUTPUT)/veristat		\
> +		     | extras $(BPF_OBJS)				\
> +		     $(if $(PERMISSIVE_TESTS),$(TEST_OBJS))

[Severity: Medium]
Will this break incremental test development in permissive mode?

By placing TEST_OBJS exclusively after the order-only prerequisite pipe (|)
when PERMISSIVE_TESTS is active, make is instructed to not rebuild the target
when the test objects are updated. 

If a developer modifies an existing test file while using BPF_STRICT_BUILD=0,
the test object will successfully recompile, but the test runner binary
(like test_progs) will not relink to include the new object. Does this cause
stale tests to be executed unknowingly?

> +	$(call msg,BINARY,,$@)
> +	$(Q)$(CC) $(CFLAGS)						\
> +		$(if $(PERMISSIVE_TESTS),$(wildcard $(TEST_OBJS)))	\
> +		$(filter %.a %.o,$^)					\
> +		$(LDLIBS) $(LLVM_LDLIBS) $(LDFLAGS) $(LLVM_LDFLAGS) -o $@
> +	$(Q)ln -sf $(if $(FLAVOR),..,.)/tools/build/bpftool/$(USE_BOOTSTRAP)bpftool \
> +		   $(RDIR)/bpftool

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Sashiko AI review · https://sashiko.dev/#/patchset/20260721194111.334795-1-nickolay.lysenko@gmail.com?part=3