Re: [PATCH v2 1/4] selftests: add shared lib.bpf.mk to build BPF progs and skeletons

> diff --git a/tools/testing/selftests/lib.bpf.mk b/tools/testing/selftests/lib.bpf.mk
> new file mode 100644
> index 000000000000..6f175c6568e9
> --- /dev/null
> +++ b/tools/testing/selftests/lib.bpf.mk

[ ... ]

> +# ---- libbpf (target) ------------------------------------------------------
> +# Pass ARCH/CROSS_COMPILE/CC through: lib.mk's CC is file-origin and is not
> +# exported, so without this the libbpf sub-make would rebuild for the host under
> +# a pure-LLVM cross build (make LLVM=1 ARCH=<arch>).  -fPIC keeps the static
> +# libbpf linkable into position-independent (PIE) test binaries.
> +$(BPFOBJ): $(wildcard $(BPFDIR)/*.[ch] $(BPFDIR)/Makefile) \
> +	   $(APIDIR)/linux/bpf.h | $(BUILD_DIR)/libbpf
> +	$(Q)$(MAKE) $(submake_extras) -C $(BPFDIR) OUTPUT=$(BUILD_DIR)/libbpf/ \
> +		    ARCH=$(ARCH) CROSS_COMPILE=$(CROSS_COMPILE) CC="$(CC)"     \
> +		    EXTRA_CFLAGS='-g -O0 -fPIC'				      \
> +		    DESTDIR=$(SCRATCH_DIR) prefix= all install_headers

This rule hardcodes EXTRA_CFLAGS='-g -O0 -fPIC' for the libbpf sub-make.
tools/testing/selftests/bpf/Makefile instead passes
EXTRA_CFLAGS='-g $(OPT_FLAGS) $(SAN_CFLAGS) $(EXTRA_CFLAGS)'.

With -O0 pinned here, is there a way for someone to build the selftests
(including libbpf) with -O2, or with sanitizer flags?  Could this at least
honor the EXTRA_CFLAGS or USERCFLAGS that lib.mk already defines?

The same hardcoding shows up in the host libbpf and host bpftool rules
below, so the same question applies to them:

> +# ---- libbpf (host) -- a distinct rule only when cross-compiling -----------
> +ifneq ($(BPFOBJ),$(HOST_BPFOBJ))
> +$(HOST_BPFOBJ): $(wildcard $(BPFDIR)/*.[ch] $(BPFDIR)/Makefile) \
> +		| $(HOST_BUILD_DIR)/libbpf
> +	$(Q)$(MAKE) $(submake_extras) -C $(BPFDIR) ARCH= CROSS_COMPILE=	      \
> +		    OUTPUT=$(HOST_BUILD_DIR)/libbpf/ CC=$(HOSTCC) LD=$(HOSTLD) \
> +		    EXTRA_CFLAGS='-g -O0'				      \
> +		    DESTDIR=$(HOST_SCRATCH_DIR) prefix= all install_headers
> +endif
> +
> +# ---- bpftool (host) -------------------------------------------------------
> +$(DEFAULT_BPFTOOL): $(wildcard $(BPFTOOLDIR)/*.[ch] $(BPFTOOLDIR)/Makefile) \
> +		    $(HOST_BPFOBJ) | $(HOST_BUILD_DIR)/bpftool
> +	$(Q)$(MAKE) $(submake_extras) -C $(BPFTOOLDIR)		  \
> +		    ARCH= CROSS_COMPILE= CC=$(HOSTCC) LD=$(HOSTLD) \
> +		    EXTRA_CFLAGS='-g -O0'			  \
> +		    OUTPUT=$(HOST_BUILD_DIR)/bpftool/		  \
> +		    LIBBPF_OUTPUT=$(HOST_BUILD_DIR)/libbpf/	  \
> +		    LIBBPF_DESTDIR=$(HOST_SCRATCH_DIR)/		  \
> +		    prefix= DESTDIR=$(HOST_SCRATCH_DIR)/ install-bin

[ ... ]

On the commit message:

>     This saves much work for configuring selftests in other folder, such the cgroup.

This isn't a bug, but could this sentence be tightened?  "in other
folder" and "such the cgroup" read a little awkwardly, and the preceding
text already explains the deduplication rationale.  Perhaps something like
"This eases adding BPF-based selftests in other directories, such as
cgroup."


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/29908293077