Re: [PATCH bpf] bpf, docs: Correct the example of BPF_XOR

[Zheng Yejian]

On 2022/11/30 02:54, David Vernet wrote:
> 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@xxxxxxxxxx>
> > ---
> >   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

See Chapter 'Instruction classes', BPF_K means "use 32-bit immediate as 
source operand", so it should be 'imm32' instead of 'src_reg'.

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