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 [off-list ref] wrote:

On Wed, Feb 19, 2020 at 01:30:12PM +0100, Jesper Dangaard Brouer wrote:

quoted

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/.

quoted

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).

 

quoted

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