Re: [PATCH] xen/arm32: head: Update the documentation for register r12

[Michal Orzel <michal.orzel@xxxxxxx>]

Hi Julien,

On 28.02.2022 11:11, Julien Grall wrote:
> From: Julien Grall <jgrall@xxxxxxxxxx>
> 
> Since commit 54c4ae18d158 ("xen/arm32: head: Rework and document
> launch()"), the boot code is not using the register r12.
> 
> So update the documentation to show r12 has no specific purpose.
> 
> Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
> ---
>  xen/arch/arm/arm32/head.S | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
> index 13cfc837d39c..78274a1c034f 100644
> --- a/xen/arch/arm/arm32/head.S
> +++ b/xen/arch/arm/arm32/head.S
> @@ -79,7 +79,7 @@
>   *   r9  - paddr(start)
>   *   r10 - phys offset
>   *   r11 - UART address
> - *   r12 - is_secondary_cpu
> + *   r12 -
>   *   r13 - SP
>   *   r14 - LR
>   *   r15 - PC
> 

FWICS, there are still 2 instructions in this file assigning #0 or #1 to r12 
and each of them
has a comment "/* r12 := is_secondary_cpu */". 

So I have 2 questions:
1. Do we even need these instructions? (I do not think so)
2. If we need these instructions, do we need these comments?

Cheers,
Michal