linux-kernel - Re: [PATCH] perf build: Support passing extra Clang options via EXTRA_BPF

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Message-ID: <20251125161026.GF724103@e132581.arm.com>
Date: Tue, 25 Nov 2025 16:10:26 +0000
From: Leo Yan <leo.yan@....com>
To: hupu <hupu.gm@...il.com>
Cc: Namhyung Kim <namhyung@...nel.org>, acme@...nel.org,
	adrian.hunter@...el.com, alexander.shishkin@...ux.intel.com,
	irogers@...gle.com, jolsa@...nel.org, justinstitt@...gle.com,
	linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
	mark.rutland@....com, mingo@...hat.com, morbo@...gle.com,
	nathan@...nel.org, nick.desaulniers+lkml@...il.com,
	peterz@...radead.org
Subject: Re: [PATCH] perf build: Support passing extra Clang options via
 EXTRA_BPF_FLAGS

On Tue, Nov 25, 2025 at 09:07:26PM +0800, hupu wrote:

[...]

> --- a/tools/perf/Makefile.perf
> +++ b/tools/perf/Makefile.perf
> @@ -35,6 +35,9 @@ include ../scripts/utilities.mak
>  #
>  # Define EXTRA_CFLAGS=-m64 or EXTRA_CFLAGS=-m32 as appropriate for
> cross-builds.
>  #
> +# Define EXTRA_BPF_FLAGS="--sysroot=<path>" or other custom include paths for
> +# cross-compiling BPF skeletons
> +#
>  # Define EXCLUDE_EXTLIBS=-lmylib to exclude libmylib from the auto-generated
>  # EXTLIBS.
>  #
> @@ -1252,7 +1255,7 @@ endif
>  $(SKEL_TMP_OUT)/%.bpf.o: $(OUTPUT)PERF-VERSION-FILE
> util/bpf_skel/perf_version.h | $(SKEL_TMP_OUT)
>  $(SKEL_TMP_OUT)/%.bpf.o: util/bpf_skel/%.bpf.c $(LIBBPF) $(SKEL_OUT)/vmlinux.h
>   $(QUIET_CLANG)$(CLANG) -g -O2 -fno-stack-protector --target=bpf \
> -   $(CLANG_OPTIONS) $(BPF_INCLUDE) $(TOOLS_UAPI_INCLUDE) \
> +   $(CLANG_OPTIONS) $(EXTRA_BPF_FLAGS) $(BPF_INCLUDE) $(TOOLS_UAPI_INCLUDE) \

I am concerned for this change.

How can you only build eBPF skel program with "--sysroot" but not
applying the same build env on perf binary and associated libs (libperf,
bpftool, etc) ?

For a convinced solution, I'd expect we can apply PKG_CONFIG_SYSROOT_DIR
for both normal perf build and eBPF skel build.  More important, please
provide steps for how to build perf with a SDK.

Thanks,
Leo