linux-kernel - Re: [PATCH bpf-next v2] bpf: Propagate memory bounds to registers in atomics w/ BPF

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Date:   Mon, 1 Feb 2021 15:27:26 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Brendan Jackman <jackmanb@...gle.com>
Cc:     bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Florent Revest <revest@...omium.org>,
        John Fastabend <john.fastabend@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next v2] bpf: Propagate memory bounds to registers in
 atomics w/ BPF_FETCH

On Mon, Feb 1, 2021 at 7:00 AM Brendan Jackman <jackmanb@...gle.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"