linux-kernel - Re: [PATCH v3 1/7] compiler-clang: add build check for clang 10.0.1

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Date:   Tue, 3 Nov 2020 10:48:27 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Jarkko Sakkinen <jarkko@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Marco Elver <elver@...gle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Will Deacon <will@...nel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/7] compiler-clang: add build check for clang 10.0.1

On Mon, Nov 2, 2020 at 8:55 PM Jarkko Sakkinen <jarkko@...nel.org> wrote:
>
> On Wed, Sep 02, 2020 at 03:59:05PM -0700, Nick Desaulniers wrote:
> > +#define CLANG_VERSION (__clang_major__ * 10000       \
> > +                  + __clang_minor__ * 100    \
> > +                  + __clang_patchlevel__)
> > +
> > +#if CLANG_VERSION < 100001
> > +# error Sorry, your version of Clang is too old - please use 10.0.1 or newer.
> > +#endif
>
>
> I'm trying to compile a BPF enabled test kernel for a live system and I
> get this error even though I have much newer clang:
>
> ➜  ~ (master) ✔ clang --version
> Ubuntu clang version 11.0.0-2
> Target: x86_64-pc-linux-gnu
> Thread model: posix
> InstalledDir: /usr/bin
>
> Tried to Google for troubleshooter tips but this patch is basically the
> only hit I get :-)

To check the values of the above preprocessor defines, please run:
$ clang -dM -E - < /dev/null | grep -e __clang_m -e __clang_p

If you have multiple versions of clang installed, you might not be
running the version you think you are.  Particularly, if you're using
bcc, idk if it includes a copy of clang?  If that's the case, we may
have to work out how we can support older versions of clang for the
express purposes of bpf.
-- 
Thanks,
~Nick Desaulniers