linux-kernel - Re: [PATCH] libbpf: Fix build on read-only filesystems

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Date:   Sat, 21 Dec 2019 17:25:51 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] libbpf: Fix build on read-only filesystems

Hello,

On Sat, Dec 21, 2019 at 5:29 AM Andrii Nakryiko
<andrii.nakryiko@...il.com> wrote:
>
> On Thu, Dec 19, 2019 at 7:26 PM Namhyung Kim <namhyung@...nel.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@...nel.org>
> > ---
>
> Overall nothing is obviously broken, except you need to fix up
> selftests/bpf's Makefile as well.

Thanks for pointing this out.  It's because bpf selftest also needs the
bpf_helper_defs.h right?  But I'm currently having a problem with LLVM
when building the selftests.  Can you help me testing the patch below?
(It should be applied after this patch.  Are you ok with it?)


>
> BTW, this patch doesn't apply cleanly to latest bpf-next, so please rebase.
>
> Also subject prefix should look like [PATCH bpf-next] if it's meant to
> be applied against bpf-next.

Will do.

Thanks
Namhyung

-----------8<-------------
diff --git a/tools/testing/selftests/bpf/Makefile
b/tools/testing/selftests/bpf/Makefile
index 866fc1cadd7c..897877f7849b 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -151,9 +151,9 @@ $(DEFAULT_BPFTOOL): force
 $(BPFOBJ): force
        $(MAKE) -C $(BPFDIR) OUTPUT=$(OUTPUT)/

-BPF_HELPERS := $(BPFDIR)/bpf_helper_defs.h $(wildcard $(BPFDIR)/bpf_*.h)
-$(BPFDIR)/bpf_helper_defs.h:
-       $(MAKE) -C $(BPFDIR) OUTPUT=$(OUTPUT)/ bpf_helper_defs.h
+BPF_HELPERS := $(OUTPUT)/bpf_helper_defs.h $(wildcard $(BPFDIR)/bpf_*.h)
+$(OUTPUT)/bpf_helper_defs.h:
+       $(MAKE) -C $(BPFDIR) OUTPUT=$(OUTPUT)/ $(OUTPUT)/bpf_helper_defs.h

 # Get Clang's default includes on this system, as opposed to those seen by
 # '-target bpf'. This fixes "missing" files on some architectures/distros,