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From:   Brendan Jackman <jackmanb@google.com>
Date:   Tue, 2 Feb 2021 11:31:26 +0100
Message-ID: <CA+i-1C2ZWUbGxWJ8kAxbri9rBboyuMaVj_BBhg+2Zf_Su9BOJA@mail.gmail.com>
Subject: Re: [PATCH bpf-next v2] bpf: Propagate memory bounds to registers in
 atomics w/ BPF_FETCH
To:     Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc:     bpf <bpf@vger.kernel.org>, Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii.nakryiko@gmail.com>,
        KP Singh <kpsingh@chromium.org>,
        Florent Revest <revest@chromium.org>,
        John Fastabend <john.fastabend@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>
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On Tue, 2 Feb 2021 at 00:27, Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Mon, Feb 1, 2021 at 7:00 AM Brendan Jackman <jackmanb@google.com> wrote:
> > +
> > +SEC("fentry/bpf_fentry_test1")
> > +int BPF_PROG(sub, int x)
> > +{
> > +       int a = 0;
> > +       int b = __sync_fetch_and_add(&a, 1);
>
> It probably needs ENABLE_ATOMICS_TESTS ?
>
> Otherwise clang without -mcpu=v3 will complain:
> "fatal error: error in backend: Invalid usage of the XADD return value"

Ah yep of course, thanks for spotting. v3 incoming...