Re: [PATCH 12/15] ebpf-docs: Add Linux note about register calling convention

From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: dthaler1968@googlemail.com
Cc: bpf@vger.kernel.org, Dave Thaler <dthaler@microsoft.com>
Subject: Re: [PATCH 12/15] ebpf-docs: Add Linux note about register calling convention
Date: Fri, 30 Sep 2022 15:17:48 -0700	[thread overview]
Message-ID: <20220930221748.eknsxrfnzio2uouf@macbook-pro-4.dhcp.thefacebook.com> (raw)
In-Reply-To: <20220927185958.14995-12-dthaler1968@googlemail.com>

On Tue, Sep 27, 2022 at 06:59:55PM +0000, dthaler1968@googlemail.com wrote:
> From: Dave Thaler <dthaler@microsoft.com>
> 
> Signed-off-by: Dave Thaler <dthaler@microsoft.com>
> ---
>  Documentation/bpf/linux-notes.rst | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/Documentation/bpf/linux-notes.rst b/Documentation/bpf/linux-notes.rst
> index 522ebe27d..0581ba326 100644
> --- a/Documentation/bpf/linux-notes.rst
> +++ b/Documentation/bpf/linux-notes.rst
> @@ -7,6 +7,12 @@ Linux implementation notes
>  
>  This document provides more details specific to the Linux kernel implementation of the eBPF instruction set.
>  
> +Registers and calling convention
> +================================
> +
> +All program types only use R1 which contains the "context", which is typically a structure containing all
> +the inputs needed, and the exit value for eBPF programs is passed as a 32 bit value.

There is a patch pending that makes return values 64-bit.
Also bpf progs that replace other bpf progs have all 5 input args.
I think this paragraph is unnecessary.

> +
>  Arithmetic instructions
>  =======================
>  
> -- 
> 2.33.4
> 