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

On Wed, Feb 19, 2020 at 10:29 AM Jesper Dangaard Brouer
[off-list ref] wrote:

On Wed, 19 Feb 2020 09:38:50 -0800
Andrii Nakryiko [off-list ref] wrote:

quoted

On Wed, Feb 19, 2020 at 9:04 AM Jesper Dangaard Brouer
[off-list ref] wrote:

quoted

On Wed, 19 Feb 2020 08:41:27 -0800
Alexei Starovoitov [off-list ref] wrote:

quoted

On Wed, Feb 19, 2020 at 4:30 AM Jesper Dangaard Brouer
[off-list ref] wrote:

quoted

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.

...

quoted

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.

The latest Clang is 9.0.1, and it doesn't build with that.

Latest as in "latest built from sources".

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