netdev - Re: BPF selftests build failure in 5.10-rc

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Date:   Wed, 9 Dec 2020 16:15:35 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Seth Forshee <seth.forshee@...onical.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: BPF selftests build failure in 5.10-rc

On Wed, Dec 9, 2020 at 2:24 PM Seth Forshee <seth.forshee@...onical.com> wrote:
>
> Building the BPF selftests with clang 11, I'm getting the following
> error:
>
>    CLNG-LLC [test_maps] profiler1.o
>  In file included from progs/profiler1.c:6:
>  progs/profiler.inc.h:260:17: error: use of unknown builtin '__builtin_preserve_enum_value' [-Wimplicit-function-declaration]
>                  int cgrp_id = bpf_core_enum_value(enum cgroup_subsys_id___local,
>                                ^
>  /home/ubuntu/unstable/tools/testing/selftests/bpf/tools/include/bpf/bpf_core_read.h:179:2: note: expanded from macro 'bpf_core_enum_value'
>          __builtin_preserve_enum_value(*(typeof(enum_type) *)enum_value, BPF_ENUMVAL_VALUE)
>          ^
>  1 error generated.
>  llc: error: llc: <stdin>:1:1: error: expected top-level entity
>  BPF obj compilation failed

Addressed by fb3558127cb6 ("bpf: Fix selftest compilation on clang 11")

>
> I see that test_core_reloc_enumval.c takes precautions around the use of
> __builtin_preserve_enum_value as it is currently only available in clang
> 12 nightlies. Is it possible to do something similar here? Though I see
> that the use of the builtin is not nearly so neatly localized as it is
> in test_core_reloc_enumval.c.
>
> Thanks,
> Seth