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

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Message-ID: <20200219132856.GA2836367@kroah.com>
Date:   Wed, 19 Feb 2020 14:28:56 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Andrii Nakryiko <andriin@...com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        BPF-dev-list <bpf@...r.kernel.org>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Daniel Borkmann <borkmann@...earbox.net>,
        David Miller <davem@...emloft.net>,
        LKML <linux-kernel@...r.kernel.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 01:30:12PM +0100, Jesper Dangaard Brouer wrote:
> Hi Andrii,
> 
> Downloaded tarball for kernel release 5.5.4, and I cannot compile
> tools/testing/selftests/bpf/ with latest LLVM release version 9.

Is this something that recently broke?  If so, what commit caused it?

And has llvm 9 always worked here?

> Looking closer at the build error messages, I can see that this is
> caused by using LLVM features that (I assume) will be avail in release
> 10. I find it very strange that we can release a kernel that have build
> dependencies on a unreleased version of LLVM.

Is this the first time you have tried using llvm to build a kernel?
This isn't a new thing :)

> I love the new LLVM BTF features, but we cannot break users/CI-systems
> that wants to run the BPF-selftests.

Is this a regression from older kernels?

And does gcc work?

thanks,

greg k-h