linux-kernel - Re: [PATCH v2] bpf: Fix BTF_ID symbol generation collision

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Message-ID: <CAADnVQJVL7yo5ZrBZ99xO-MWHHg8L-SuSJrCTf-eUd-k5UO75g@mail.gmail.com>
Date:   Fri, 15 Sep 2023 10:21:48 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, stable <stable@...r.kernel.org>,
        Satya Durga Srinivasu Prabhala <quic_satyap@...cinc.com>,
        Marcus Seyfarth <m.seyfarth@...il.com>,
        Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH v2] bpf: Fix BTF_ID symbol generation collision

On Fri, Sep 15, 2023 at 10:18 AM Nathan Chancellor <nathan@...nel.org> wrote:
>
> On Fri, Sep 15, 2023 at 09:42:20AM -0700, Nick Desaulniers wrote:
> > Marcus and Satya reported an issue where BTF_ID macro generates same
> > symbol in separate objects and that breaks final vmlinux link.
> >
> >   ld.lld: error: ld-temp.o <inline asm>:14577:1: symbol
> >   '__BTF_ID__struct__cgroup__624' is already defined
> >
> > This can be triggered under specific configs when __COUNTER__ happens to
> > be the same for the same symbol in two different translation units,
> > which is already quite unlikely to happen.
> >
> > Add __LINE__ number suffix to make BTF_ID symbol more unique, which is
> > not a complete fix, but it would help for now and meanwhile we can work
> > on better solution as suggested by Andrii.
> >
> > Cc: stable@...r.kernel.org
> > Reported-by: Satya Durga Srinivasu Prabhala <quic_satyap@...cinc.com>
> > Reported-by: Marcus Seyfarth <m.seyfarth@...il.com>
> > Closes: https://github.com/ClangBuiltLinux/linux/issues/1913
> > Tested-by: Marcus Seyfarth <m.seyfarth@...il.com>
> > Debugged-by: Nathan Chancellor <nathan@...nel.org>
> > Co-developed-by: Jiri Olsa <jolsa@...nel.org>
> > Link: https://lore.kernel.org/bpf/CAEf4Bzb5KQ2_LmhN769ifMeSJaWfebccUasQOfQKaOd0nQ51tw@mail.gmail.com/
> > Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
> > ---
> >  tools/include/linux/btf_ids.h | 2 +-
>
> Shouldn't this diff be in include/linux/btf_ids.h as well? Otherwise, I
> don't think it will be used by the kernel build.

argh.
Let's do this patch as-is and another patch to update everything
in tools/../btf_ids.h, since it got out of sync quite a bit.