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From:   Andrii Nakryiko <andrii.nakryiko@gmail.com>
Date:   Fri, 20 Dec 2019 14:01:50 -0800
Message-ID: <CAEf4BzahazYCzutyULrugwjjz-Fxg_rzJ8v+pXUKpsmzpsHfJQ@mail.gmail.com>
Subject: Re: [PATCH] libbpf: Fix build on read-only filesystems
To:     Namhyung Kim <namhyung@kernel.org>
Cc:     Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        Andrii Nakryiko <andriin@fb.com>, bpf <bpf@vger.kernel.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Jiri Olsa <jolsa@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>
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On Thu, Dec 19, 2019 at 7:26 PM Namhyung Kim <namhyung@kernel.org> wrote:
>
> I got the following error when I tried to build perf on a read-only
> filesystem with O=dir option.
>
>   $ cd /some/where/ro/linux/tools/perf
>   $ make O=$HOME/build/perf
>   ...
>     CC       /home/namhyung/build/perf/lib.o
>   /bin/sh: bpf_helper_defs.h: Read-only file system
>   make[3]: *** [Makefile:184: bpf_helper_defs.h] Error 1
>   make[2]: *** [Makefile.perf:778: /home/namhyung/build/perf/libbpf.a] Error 2
>   make[2]: *** Waiting for unfinished jobs....
>     LD       /home/namhyung/build/perf/libperf-in.o
>     AR       /home/namhyung/build/perf/libperf.a
>     PERF_VERSION = 5.4.0
>   make[1]: *** [Makefile.perf:225: sub-make] Error 2
>   make: *** [Makefile:70: all] Error 2
>
> It was becaused bpf_helper_defs.h was generated in current directory.
> Move it to OUTPUT directory.
>
> Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> ---
>  tools/lib/bpf/Makefile | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
> index 99425d0be6ff..2f42a35f4634 100644
> --- a/tools/lib/bpf/Makefile
> +++ b/tools/lib/bpf/Makefile
> @@ -159,7 +159,7 @@ all: fixdep
>
>  all_cmd: $(CMD_TARGETS) check
>
> -$(BPF_IN_SHARED): force elfdep bpfdep bpf_helper_defs.h
> +$(BPF_IN_SHARED): force elfdep bpfdep $(OUTPUT)bpf_helper_defs.h

btw, there is a lot of $(OUTPUT)bpf_helper_defs.h repetition, could
you please extract it into a variable, similar to BPF_IN_SHARED and
others? E.g., just BPF_HELPER_DEFS would work. Thanks!

>         @(test -f ../../include/uapi/linux/bpf.h -a -f ../../../include/uapi/linux/bpf.h && ( \
>         (diff -B ../../include/uapi/linux/bpf.h ../../../include/uapi/linux/bpf.h >/dev/null) || \
>         echo "Warning: Kernel ABI header at 'tools/include/uapi/linux/bpf.h' differs from latest version at 'include/uapi/linux/bpf.h'" >&2 )) || true
> @@ -177,12 +177,12 @@ $(BPF_IN_SHARED): force elfdep bpfdep bpf_helper_defs.h
>         echo "Warning: Kernel ABI header at 'tools/include/uapi/linux/if_xdp.h' differs from latest version at 'include/uapi/linux/if_xdp.h'" >&2 )) || true
>         $(Q)$(MAKE) $(build)=libbpf OUTPUT=$(SHARED_OBJDIR) CFLAGS="$(CFLAGS) $(SHLIB_FLAGS)"

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