netdev - Re: [PATCH bpf-next] bpf, x86: remove unnecessary handling of BPF

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Message-ID: <CA+i-1C2HBja-8Am4gHkcrYdkruw0+sOaGDejc9DS-HfYVXVfyQ@mail.gmail.com>
Date:   Thu, 27 Jan 2022 11:48:02 +0100
From:   Brendan Jackman <jackmanb@...gle.com>
To:     Hou Tao <houtao1@...wei.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Martin KaFai Lau <kafai@...com>, Yonghong Song <yhs@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next] bpf, x86: remove unnecessary handling of BPF_SUB
 atomic op

Yep - BPF_SUB is also excluded in Documentation/networking/filter.rst,
plus the interpreter and verifier don't support it.

Thanks,

Acked-by: Brendan Jackman <jackmanb@...gle.com>


On Thu, 27 Jan 2022 at 09:17, Hou Tao <houtao1@...wei.com> wrote:
>
> According to the LLVM commit (https://reviews.llvm.org/D72184),
> sync_fetch_and_sub() is implemented as a negation followed by
> sync_fetch_and_add(), so there will be no BPF_SUB op and just
> remove it.
>
> Signed-off-by: Hou Tao <houtao1@...wei.com>
> ---
>  arch/x86/net/bpf_jit_comp.c | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> index ce1f86f245c9..5d643ebb1e56 100644
> --- a/arch/x86/net/bpf_jit_comp.c
> +++ b/arch/x86/net/bpf_jit_comp.c
> @@ -787,7 +787,6 @@ static int emit_atomic(u8 **pprog, u8 atomic_op,
>         /* emit opcode */
>         switch (atomic_op) {
>         case BPF_ADD:
> -       case BPF_SUB:
>         case BPF_AND:
>         case BPF_OR:
>         case BPF_XOR:
> --
> 2.29.2
>