netdev - Re: Kernel 5.5.4 build fail for BPF-selftests with latest LLVM

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Date:   Wed, 19 Feb 2020 09:38:50 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Andrii Nakryiko <andriin@...com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        BPF-dev-list <bpf@...r.kernel.org>,
        Daniel Borkmann <borkmann@...earbox.net>,
        David Miller <davem@...emloft.net>,
        LKML <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Anders Roxell <anders.roxell@...aro.org>,
        Toke Høiland-Jørgensen <toke@...hat.com>
Subject: Re: Kernel 5.5.4 build fail for BPF-selftests with latest LLVM

On Wed, Feb 19, 2020 at 9:04 AM Jesper Dangaard Brouer
<brouer@...hat.com> wrote:
>
> On Wed, 19 Feb 2020 08:41:27 -0800
> Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:
>
> > On Wed, Feb 19, 2020 at 4:30 AM Jesper Dangaard Brouer
> > <brouer@...hat.com> wrote:
> > >
> > > I'm willing to help out, such that we can do either version or feature
> > > detection, to either skip compiling specific test programs or at least
> > > give users a proper warning of they are using a too "old" LLVM version.
> > ...
> > > progs/test_core_reloc_bitfields_probed.c:47:13: error: use of unknown builtin '__builtin_preserve_field_info' [-Wimplicit-function-declaration]
> > >         out->ub1 = BPF_CORE_READ_BITFIELD_PROBED(in, ub1);
> >
> > imo this is proper warning message already.
>
> This is an error, not a warning.  The build breaks as the make process stops.
>

Latest Clang was a requirement for building and running all selftests
for a long time now. There were few previous discussions on mailing
list about this and each time the conclusion was the same: latest
Clang is a requirement for BPF selftests.

> --
> Best regards,
>   Jesper Dangaard Brouer
>   MSc.CS, Principal Kernel Engineer at Red Hat
>   LinkedIn: http://www.linkedin.com/in/brouer
>