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

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Message-ID: <20200219144254.36c3921b@carbon>
Date:   Wed, 19 Feb 2020 14:42:54 +0100
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
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>, brouer@...hat.com
Subject: Re: Kernel 5.5.4 build fail for BPF-selftests with latest LLVM

On Wed, 19 Feb 2020 14:28:56 +0100
Greg Kroah-Hartman <gregkh@...uxfoundation.org> wrote:

> 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?

Digging through, it seems several commits.

> And has llvm 9 always worked here?

Yes, llvm-9 used to work for tools/testing/selftests/bpf/.


> > 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 :)

LOL - we are talking past each-other... I'm not building the entire
kernel with LLVM.  Notice I'm talking about the BPF-selftests located
in directory tools/testing/selftests/bpf/.  Building the selftests
programs are broken

We always use LLVM to build BPF programs (both samples/bpf/ and selftests).

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

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