linux-kernel - Re: [PATCH bpf] bpf, docs: Correct the example of BPF

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Message-ID: <Y4ZVUiwGnVIj/V4U@maniforge.lan>
Date:   Tue, 29 Nov 2022 12:54:10 -0600
From:   David Vernet <void@...ifault.com>
To:     Zheng Yejian <zhengyejian1@...wei.com>
Cc:     ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
        martin.lau@...ux.dev, song@...nel.org, yhs@...com,
        john.fastabend@...il.com, kpsingh@...nel.org, sdf@...gle.com,
        haoluo@...gle.com, jolsa@...nel.org, corbet@....net,
        bpf@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf] bpf, docs: Correct the example of BPF_XOR

On Tue, Nov 29, 2022 at 09:45:58PM +0800, Zheng Yejian wrote:
> Refer to description of BPF_XOR, dst_reg should be used but not src_reg
> in the examples.
> 
> Signed-off-by: Zheng Yejian <zhengyejian1@...wei.com>
> ---
>  Documentation/bpf/instruction-set.rst | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/bpf/instruction-set.rst b/Documentation/bpf/instruction-set.rst
> index 5d798437dad4..e672d5ec6cc7 100644
> --- a/Documentation/bpf/instruction-set.rst
> +++ b/Documentation/bpf/instruction-set.rst
> @@ -122,11 +122,11 @@ BPF_END   0xd0   byte swap operations (see `Byte swap instructions`_ below)
>  
>  ``BPF_XOR | BPF_K | BPF_ALU`` means::
>  
> -  src_reg = (u32) src_reg ^ (u32) imm32
> +  dst_reg = (u32) dst_reg ^ (u32) imm32

Shouldn't this be 

dst_reg = (u32) dst_reg ^ (u32) src_reg

Same idea below for 64 bit

>  
>  ``BPF_XOR | BPF_K | BPF_ALU64`` means::
>  
> -  src_reg = src_reg ^ imm32
> +  dst_reg = dst_reg ^ imm32
>  
>  
>  Byte swap instructions
> -- 
> 2.25.1
>