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

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Message-ID: <CADHxFxR2t4jMmjm3hMdhsxoRjUw+k3CtrG6ZzG39b_BhVzyzsQ@mail.gmail.com>
Date: Tue, 18 Nov 2025 15:18:45 +0800
From: hupu <hupu.gm@...il.com>
To: Leo Yan <leo.yan@....com>, Namhyung Kim <namhyung@...nel.org>
Cc: 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

Hi Leo and Namhyung,
Sorry for the late response, and thanks for the guidance on
prioritizing self-contained headers from the kernel source.


> > > To be clear, now we are not talking cross build for perf program or any
> > > targeting a CPU arch, it is a build failure for eBPF program.
> > >
> >
> > I’d like to clarify the background and scenario once more:
> > I’m building an SDK that includes a cross-compilation toolchain for
> > the target architecture along with a copy of the kernel source tree.
>
> I am not preventing to use toolchains in you mentioned SDK.  I just
> prefer to give priority the headers provided by the kernel source.
>
> Seems to me, a more reasonable series would be:
>
>  - Fix the eBPF program build with using self-contained headers;
>  - Extend to support external headers.
>


I added the following diagnostic output to Makefile.perf to print
CLANG_OPTIONS, BPF_INCLUDE, and TOOLS_UAPI_INCLUDE during compilation,
to identify the header search paths used when building the eBPF
program.


diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
index 47c906b807ef..33fe2d8f16c6 100644
--- a/tools/perf/Makefile.perf
+++ b/tools/perf/Makefile.perf
@@ -1249,6 +1249,12 @@ else
        $(Q)cp "$(VMLINUX_H)" $@
 endif

+$(warning AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
+$(warning CLANG_OPTIONS: $(CLANG_OPTIONS))
+$(warning BPF_INCLUDE: $(BPF_INCLUDE))
+$(warning TOOLS_UAPI_INCLUDE: $(TOOLS_UAPI_INCLUDE))
+$(warning AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA)
+
 $(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 \


The compilation output is as follows:


Makefile.perf:1252: AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
Makefile.perf:1253: CLANG_OPTIONS: -Wall -Werror
Makefile.perf:1254: BPF_INCLUDE:
-I/home/hupu/work/code/explore/output/build-mainline/tools/perf/util/bpf_skel/.tmp/..
-I/home/hupu/work/code/explore/output/build-mainline/tools/perf/libbpf/include
-idirafter /usr/lib/llvm-18/lib/clang/18/include -idirafter
/usr/local/include -idirafter /usr/include
Makefile.perf:1255: TOOLS_UAPI_INCLUDE:
-I/home/hupu/work/code/explore/linux-mainline/tools/include/uapi
Makefile.perf:1256: AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA


>From the above BPF_INCLUDE and TOOLS_UAPI_INCLUDE prints, perf was not
prioritizing the kernel’s self-contained headers when compiling the
eBPF program.

I then added KHDR_INCLUDES to BPF_INCLUDE, pointing it to the kernel’s
self-contained header directory so that the build prefers headers
provided by the kernel.


diff --git a/tools/perf/Makefile.perf b/tools/perf/Makefile.perf
index 47c906b807ef..65c6e871988b 100644
--- a/tools/perf/Makefile.perf
+++ b/tools/perf/Makefile.perf
@@ -1202,7 +1202,8 @@ endif

 CLANG_OPTIONS = -Wall
 CLANG_SYS_INCLUDES = $(call get_sys_includes,$(CLANG),$(CLANG_TARGET_ARCH))
-BPF_INCLUDE := -I$(SKEL_TMP_OUT)/.. -I$(LIBBPF_INCLUDE) $(CLANG_SYS_INCLUDES)
+KHDR_INCLUDES := $(abspath $(OUTPUT)/../../usr/include)
+BPF_INCLUDE := -I$(SKEL_TMP_OUT)/.. -I$(LIBBPF_INCLUDE)
-I$(KHDR_INCLUDES) $(CLANG_SYS_INCLUDES)
 TOOLS_UAPI_INCLUDE := -I$(srctree)/tools/include/uapi

 ifneq ($(WERROR),0)


With this change verified, perf compiles successfully even without
explicitly specifying the cross-toolchain sysroot in the compile
command.

Therefore, before sending PATCH v4, I would appreciate your review and
any suggestions.

Thanks,
hupu