linux-kernel - Re: [PATCH] selftests/bpf: ignore pointer types check with clang

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Date:   Fri, 14 Apr 2023 18:15:41 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Andrea Righi <andrea.righi@...onical.com>
Cc:     Ilya Leoshkevich <iii@...ux.ibm.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>, Hao Luo <haoluo@...gle.com>,
        Jiri Olsa <jolsa@...nel.org>, Mykola Lysenko <mykolal@...com>,
        Shuah Khan <shuah@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>,
        Paolo Pisati <paolo.pisati@...onical.com>,
        bpf <bpf@...r.kernel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        clang-built-linux <llvm@...ts.linux.dev>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] selftests/bpf: ignore pointer types check with clang

On Fri, Apr 14, 2023 at 9:28 AM Andrea Righi <andrea.righi@...onical.com> wrote:
>
> On Fri, Apr 14, 2023 at 06:15:38PM +0200, Ilya Leoshkevich wrote:
> > On Fri, Apr 14, 2023 at 08:15:03AM +0200, Andrea Righi wrote:
> > > On Thu, Apr 13, 2023 at 09:56:00PM -0700, Alexei Starovoitov wrote:
> > > > On Wed, Apr 12, 2023 at 2:59 AM Andrea Righi <andrea.righi@...onical.com> wrote:
> > > > >
> > > > > Building bpf selftests with clang can trigger errors like the following:
> > > > >
> > > > >   CLNG-BPF [test_maps] bpf_iter_netlink.bpf.o
> > > > > progs/bpf_iter_netlink.c:32:4: error: incompatible pointer types assigning to 'struct sock *' from 'struct sock___17 *' [-Werror,-Wincompatible-pointer-types]
> > > > >         s = &nlk->sk;
> > > > >           ^ ~~~~~~~~
> > > > > 1 error generated.
> > > >
> > > > I cannot reproduce this and BPF CI doesn't complain about it either.
> > > > What kind of clang do you use?
> > > > Some special version and build flags?
> > >
> > > I'm using Ubuntu clang version 15.0.7 (Ubuntu 23.04), no special build
> > > flag (unless Ubuntu enables some different default flags, but it
> > > shouldn't be the case... I'll double check).
> > >
> > > -Andrea
> >
> > Hi,
> >
> > FWIW, I see similar errors when I don't use recent pahole.
>
> I'm using pahole v1.24.

I believe Ilya is correct.

struct sock___17 is likely coming from vmlinux.h
Which means that there were errors due vmlinux build which
caused multiple structs to be present in BTF
and therefore bpftool generated such broken vmlinux.h

The BTF section in such vmlinux is likely much larger than normal.
Let's get to the bottom of it instead of masking build error.

Please try pahole 1.25.