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From: Brendan Jackman <jackmanb@google.com>
To: Hou Tao <houtao1@huawei.com>
Cc: Alexei Starovoitov <ast@kernel.org>,
	John Fastabend <john.fastabend@gmail.com>,
	Martin KaFai Lau <kafai@fb.com>, Yonghong Song <yhs@fb.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	"David S . Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>,
	netdev@vger.kernel.org, bpf <bpf@vger.kernel.org>
Subject: Re: [PATCH bpf-next] bpf, x86: remove unnecessary handling of BPF_SUB atomic op
Date: Thu, 27 Jan 2022 11:48:02 +0100	[thread overview]
Message-ID: <CA+i-1C2HBja-8Am4gHkcrYdkruw0+sOaGDejc9DS-HfYVXVfyQ@mail.gmail.com> (raw)
In-Reply-To: <20220127083240.1425481-1-houtao1@huawei.com>

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@google.com>


On Thu, 27 Jan 2022 at 09:17, Hou Tao <houtao1@huawei.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@huawei.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
>

  reply	other threads:[~2022-01-27 10:48 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-27  8:32 [PATCH bpf-next] bpf, x86: remove unnecessary handling of BPF_SUB atomic op Hou Tao
2022-01-27 10:48 ` Brendan Jackman [this message]
2022-01-27 21:51   ` Daniel Borkmann
2022-01-28  2:40     ` John Fastabend
2022-01-27 21:50 ` patchwork-bot+netdevbpf

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