Re: [RFC] perf build: Allow passing extra Clang flags via EXTRA_CLANG_FLAGS

[hupu <hupu.gm@gmail.com>]

Hi lan,
Thank you very much for your reply.

On Mon, Oct 13, 2025 at 11:46 PM Ian Rogers <irogers@google.com> wrote:
>
> On Mon, Oct 13, 2025 at 1:08 AM hupu <hupu.gm@gmail.com> wrote:
> >
> > Hi Maintainer,
> >
> > I encountered some issues while cross-compiling perf (ARCH=arm64),
> > particularly when enabling the BPF option. During the build, Clang
> > fails to compile BPF programs due to missing header files. The
> > relevant error messages are as follows:
>
> Thanks for reporting this issue! There has been some recent work in
> this area by Leo:
> https://lore.kernel.org/lkml/20251006-perf_build_android_ndk-v3-0-4305590795b2@arm.com/
> The patches are in Linux v6.18-rc1. Perhaps you could try repeating
> your build with this tree and reporting issues?
>

My local code is already updated to the latest version, and the
current commit is exactly at tag: v6.18-rc1:

commit 3a8660878839faadb4f1a6dd72c3179c1df56787 (tag: v6.18-rc1,
origin/master, origin/HEAD)
Author: Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sun Oct 12 13:42:36 2025 -0700

    Linux 6.18-rc1

However, building with this version still gives the same error as
before — when Clang tries to compile the BPF programs, it fails due to
a missing asm/ioctl.h header file.

----------------------------------------------------------
  INSTALL libsubcmd_headers
  INSTALL libsymbol_headers
  SYSHDR  /home/hupu/work/code/explore/output/build-mainline/tools/perf/libperf/arch/arm64/include/generated/uapi/asm/unistd_64.h
  INSTALL libapi_headers
  INSTALL libperf_headers
  CC      /home/hupu/work/code/explore/output/build-mainline/tools/perf/libperf/evsel.o
  INSTALL libbpf_headers
  CLANG   /home/hupu/work/code/explore/output/build-mainline/tools/perf/util/bpf_skel/.tmp/bpf_prog_profiler.bpf.o
  CLANG   /home/hupu/work/code/explore/output/build-mainline/tools/perf/util/bpf_skel/.tmp/bperf_leader.bpf.o
  CLANG   /home/hupu/work/code/explore/output/build-mainline/tools/perf/util/bpf_skel/.tmp/bperf_follower.bpf.o
In file included from <built-in>:2:
In file included from ./util/bpf_skel/perf_version.h:6:
In file included from
/home/hupu/work/code/explore/output/build-mainline/tools/perf/util/bpf_skel/.tmp/../vmlinux.h:7:
In file included from
/home/hupu/work/code/explore/linux-mainline/tools/include/uapi/linux/perf_event.h:19:
/usr/include/linux/ioctl.h:5:10: fatal error: 'asm/ioctl.h' file not found
    5 | #include <asm/ioctl.h>
      |          ^~~~~~~~~~~~~
In file included from <built-in>:2:
In file included from ./util/bpf_skel/perf_version.h:6:
In file included from
/home/hupu/work/code/explore/output/build-mainline/tools/perf/util/bpf_skel/.tmp/../vmlinux.h:7:
In file included from
/home/hupu/work/code/explore/linux-mainline/tools/include/uapi/linux/perf_event.h:19:
/usr/include/linux/ioctl.h:5:10: fatal error: 'asm/ioctl.h' file not found
    5 | #include <asm/ioctl.h>
      |          ^~~~~~~~~~~~~
In file included from <built-in>:2:
In file included from ./util/bpf_skel/perf_version.h:6:
In file included from
/home/hupu/work/code/explore/output/build-mainline/tools/perf/util/bpf_skel/.tmp/../vmlinux.h:7:
In file included from
/home/hupu/work/code/explore/linux-mainline/tools/include/uapi/linux/perf_event.h:19:
/usr/include/linux/ioctl.h:5:10: fatal error: 'asm/ioctl.h' file not found
    5 | #include <asm/ioctl.h>
      |          ^~~~~~~~~~~~~
11 error generated.
 error generated.
make[3]: *** [Makefile.perf:1259:
/home/hupu/work/code/explore/output/build-mainline/tools/perf/util/bpf_skel/.tmp/bperf_leader.bpf.o]
Error 1
make[3]: *** Waiting for unfinished jobs....
make[3]: *** [Makefile.perf:1259:
/home/hupu/work/code/explore/output/build-mainline/tools/perf/util/bpf_skel/.tmp/bpf_prog_profiler.bpf.o]
Error 1
1 error generated.
make[3]: *** [Makefile.perf:1259:
/home/hupu/work/code/explore/output/build-mainline/tools/perf/util/bpf_skel/.tmp/bperf_follower.bpf.o]
Error 1
  LD      /home/hupu/work/code/explore/output/build-mainline/tools/perf/libperf/libperf-in.o
  AR      /home/hupu/work/code/explore/output/build-mainline/tools/perf/libperf/libperf.a
make[2]: *** [Makefile.perf:289: sub-make] Error 2
make[1]: *** [Makefile:76: all] Error 2
make: *** [Makefile:93: perf] Error 2
----------------------------------------------------------

However, when I apply the previous PATCH and explicitly specify the
sysroot of the cross toolchain via the EXTRA_CLANG_FLAGS setting, the
build succeeds:

    SYSROOT=$(${CROSS_COMPILE}gcc --print-sysroot)
    EXTRA_CLANG_FLAGS="--sysroot=$SYSROOT"
    make perf ARCH=$ARCH CROSS_COMPILE=$CROSS_COMPILE
EXTRA_CLANG_FLAGS="$EXTRA_CLANG_FLAGS"

Please let me know if you need any more details or testing.

Thanks,
hupu