Re: [PATCH v4 1/4] selftests: add shared lib.bpf.mk to build BPF progs and skeletons

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] Order-only prerequisite on stamp file prevents rebuilding dependent objects when vmlinux.h changes.
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commit f7b71013493f3d0a8611d16b18e727d7b737042f
Author: Ziyang Men <ziyang.meme@gmail.com>

selftests: add shared lib.bpf.mk to build BPF progs and skeletons

This patch adds a shared Makefile fragment (lib.bpf.mk) to standardize the
build tool-chain for BPF programs and skeletons across selftests. It
centralizes the build logic to reduce duplication as more subsystems adopt
BPF-based tests.

> diff --git a/tools/testing/selftests/lib.bpf.mk b/tools/testing/selftests/lib.bpf.mk
> new file mode 100644
> index 0000000000000..f27cd1889e7ff
> --- /dev/null
> +++ b/tools/testing/selftests/lib.bpf.mk

[ ... ]

> +# ---- build vmlinux.h ------------------------------------------------------
> +lib_bpf_vmlinux_h     := $(INCLUDE_DIR)/vmlinux.h
> +lib_bpf_vmlinux_stamp := $(INCLUDE_DIR)/vmlinux.h.stamp
> +
> +# Preserve vmlinux.h's timestamp when its contents do not change.
> +ifeq ($(wildcard $(lib_bpf_vmlinux_h)),)
> +# Regenerate if the header is missing but its stamp remains.
> +.PHONY: $(lib_bpf_vmlinux_stamp)
> +endif
> +
> +# Use an order-only edge so the stamp's mtime does not propagate.
> +$(lib_bpf_vmlinux_h): | $(lib_bpf_vmlinux_stamp) ;

[Severity: Low]
Does using an order-only prerequisite here prevent rebuilding dependent
objects when vmlinux.h changes?

Using an order-only prerequisite means GNU Make might not re-stat
vmlinux.h after the stamp recipe updates it. To allow single-pass rebuilds
while avoiding redundant rebuilds when the contents haven't changed, would
it be better to use a normal dependency with the empty recipe `;`?

> +
> +$(lib_bpf_vmlinux_stamp): $(lib_bpf_vmlinux_deps) | $(INCLUDE_DIR)

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Sashiko AI review · https://sashiko.dev/#/patchset/20260908235552.2610256-1-ziyang.meme@gmail.com?part=1