Re: selftest/bpf/test_verifier_log fails on v5.11-rc5

[Jiri Olsa <jolsa@redhat.com>]

On Fri, Jan 29, 2021 at 07:13:21PM -0800, Alexei Starovoitov wrote:
> On Fri, Jan 29, 2021 at 2:15 PM Paul Moore <paul@paul-moore.com> wrote:
> >
> > On Mon, Jan 25, 2021 at 5:42 PM Alexei Starovoitov
> > <alexei.starovoitov@gmail.com> wrote:
> > > On Mon, Jan 25, 2021 at 12:54 PM Paul Moore <paul@paul-moore.com> wrote:
> > > >
> > > > Hello all,
> > > >
> > > > My apologies if this has already been reported, but I didn't see
> > > > anything obvious with a quick search through the archives.  I have a
> > > > test program that behaves very similar to the existing
> > > > selftest/bpf/test_verifier_log test that has started failing this week
> > > > with v5.11-rc5; it ran without problem last week on v5.11-rc4.  Is
> > > > this a known problem with a fix already, or is this something new?
> > > >
> > > > % uname -r
> > > > 5.11.0-0.rc5.134.fc34.x86_64
> > > > % pwd
> > > > /.../linux/tools/testing/selftests/bpf
> > > > % git log --oneline | head -n 1
> > > > 6ee1d745b7c9 Linux 5.11-rc5
> > > > % make test_verifier_log
> > > >   ...
> > > >   BINARY   test_verifier_log
> > > > % ./test_verifier_log
> > > > Test log_level 0...
> > > > Test log_size < 128...
> > > > Test log_buff = NULL...
> > > > Test oversized buffer...
> > > > ERROR: Program load returned: ret:-1/errno:22, expected ret:-1/errno:13
> > >
> > > Thanks for reporting.
> > > bpf and bpf-next don't have this issue. Not sure what changed.
> >
> > I haven't had a chance to look into this any further, but Ondrej
> > Mosnacek (CC'd) found the following today:
> >
> > "So I was trying to debug this further and I think I've identified what
> > triggers the problem. It seems that the BTF debuginfo generation
> > became broken with CONFIG_DEBUG_INFO_DWARF4=n somewhere between -rc4
> > and -rc5. It also seems to depend on a recent (Fedora Rawhide) version
> > of some component of the build system (GCC, probably), because the
> > problem disappeared when I tried to build the "bad" kernel in F33
> > buildroot instead of Rawhide."
> 
> I see. There were fixes for dwarf and btf, but I lost the track.
> I believe it was a combination of gcc bug that was worked around in pahole.
> Arnaldo, Jiri, Andrii,
> what is the status? Did all fixes land in pahole?

I checked on rawhide and besides many pahole warnings,
the resulted BTF data have many duplications in core structs

	  BTFIDS  vmlinux
	WARN: multiple IDs found for 'task_struct': 132, 1247 - using 132
	WARN: multiple IDs found for 'file': 440, 1349 - using 440
	WARN: multiple IDs found for 'inode': 698, 1645 - using 698
	WARN: multiple IDs found for 'path': 729, 1672 - using 729
	WARN: multiple IDs found for 'task_struct': 132, 2984 - using 132
	WARN: multiple IDs found for 'task_struct': 132, 3043 - using 132
	WARN: multiple IDs found for 'file': 440, 3085 - using 440
	WARN: multiple IDs found for 'seq_file': 1469, 3125 - using 1469
	WARN: multiple IDs found for 'inode': 698, 3336 - using 698
	WARN: multiple IDs found for 'path': 729, 3366 - using 729
	WARN: multiple IDs found for 'task_struct': 132, 5337 - using 132
	WARN: multiple IDs found for 'inode': 698, 5360 - using 698
	WARN: multiple IDs found for 'path': 729, 5388 - using 729
	WARN: multiple IDs found for 'file': 440, 5412 - using 440
	WARN: multiple IDs found for 'seq_file': 1469, 5639 - using 1469
	WARN: multiple IDs found for 'task_struct': 132, 6243 - using 132
	...

	# gcc --version
	gcc (GCC) 11.0.0 20210123 (Red Hat 11.0.0-0)

I'm guessing there are some DWARF changes that screwed BTF
generation.. I'll check

it's not covered by the fix I posted recently, but I think
Arnaldo is now fixing some related stuff.. Arnaldo, maybe
you are seeing same errors?

I uploaded the build log from linking part to:
  http://people.redhat.com/~jolsa/build.out.gz

jirka