netdev - Re: [PATCH bpf-next 1/2] bpftool: only build bpftool-prog-profile with clang >= v11

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Message-ID: <CAADnVQJhSEE3nuWupoUGgOU_0+OnKg4c_buMCSLyoQY3J9a_Ng@mail.gmail.com>
Date:   Tue, 10 Mar 2020 15:54:14 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Quentin Monnet <quentin@...valent.com>
Cc:     Song Liu <songliubraving@...com>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, Kernel Team <kernel-team@...com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
        Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH bpf-next 1/2] bpftool: only build bpftool-prog-profile
 with clang >= v11

On Tue, Mar 10, 2020 at 3:45 PM Quentin Monnet <quentin@...valent.com> wrote:
>
> 2020-03-10 11:36 UTC-0700 ~ Song Liu <songliubraving@...com>
> > bpftool-prog-profile requires clang of version 11.0.0 or newer. If
> > bpftool is built with older clang, show a hint of to the user.
> >
> > Signed-off-by: Song Liu <songliubraving@...com>
> > ---
> >  tools/bpf/bpftool/Makefile | 13 +++++++++++--
> >  tools/bpf/bpftool/prog.c   |  2 ++
> >  2 files changed, 13 insertions(+), 2 deletions(-)
> >
> > diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
> > index 20a90d8450f8..05a37f0f76a9 100644
> > --- a/tools/bpf/bpftool/Makefile
> > +++ b/tools/bpf/bpftool/Makefile
> > @@ -60,6 +60,15 @@ LIBS = $(LIBBPF) -lelf -lz
> >  INSTALL ?= install
> >  RM ?= rm -f
> >  CLANG ?= clang
> > +CLANG_VERS = $(shell $(CLANG) --version | head -n 1 | awk '{print $$3}')
> > +CLANG_MAJ = $(shell echo $(CLANG_VERS) | cut -d '.' -f 1)
>
> This will produce error messages on stderr if clang is not installed on
> the system.
>
> > +WITHOUT_SKELETONS = -DBPFTOOL_WITHOUT_SKELETONS
> > +
> > +ifeq ($(shell test $(CLANG_MAJ) -ge 11; echo $$?),0)
>
> Not exactly what I had in mind. I thought about the feature detection
> facility we have under tools/build/feature/, as is used for e.g.
> detecting libbfd. It would allow to check the feature is available,
> instead of tying the build to a numeric version number.

+1
I think the global data feature is actually present in v10.
Version check won't work for backported clangs.
So please do feature check.