RE: [PATCH bpf-next] bpf, docs: Add signed comparison example

John Fastabend
2023-03-14T05:00:14Z

Dave Thaler wrote:
> From: Dave Thaler <dthaler@microsoft.com>
>
> Improve clarity by adding an example of a signed comparison instruction
>
> Signed-off-by: Dave Thaler <dthaler@microsoft.com>
> ---
> Documentation/bpf/instruction-set.rst | 11 ++++++++++-
> 1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/bpf/instruction-set.rst b/Documentation/bpf/instruction-set.rst
> index 5e43e14abe8..b4464058905 100644
> --- a/Documentation/bpf/instruction-set.rst
> +++ b/Documentation/bpf/instruction-set.rst
> @@ -11,7 +11,8 @@ Documentation conventions
> =========================
>
> For brevity, this document uses the type notion "u64", "u32", etc.
> -to mean an unsigned integer whose width is the specified number of bits.
> +to mean an unsigned integer whose width is the specified number of bits,
> +and "s32", etc. to mean a signed integer of the specified number of bits.
>
> Registers and calling convention
> ================================
> @@ -264,6 +265,14 @@ BPF_JSLE 0xd0 PC += off if dst <= src signed
> The eBPF program needs to store the return value into register R0 before doing a
> BPF_EXIT.
>
> +Example:
> +
> +``BPF_JSGE | BPF_X | BPF_JMP32`` (0x7e) means::
> +
> + if (s32)dst s>= (s32)src goto +offset
> +
> +where 's>=' indicates a signed '>=' comparison.
> +
> Helper functions
> ~~~~~~~~~~~~~~~~
>

Acked-by: John Fastabend <john.fastabend@gmail.com>