Re: [PATCH v2] xen/arm32: head: Don't set r12 and update the documentation

[Bertrand Marquis <Bertrand.Marquis@xxxxxxx>]

Hi Julien,

> On 28 Feb 2022, at 13:35, Julien Grall <julien@xxxxxxx> wrote:
> 
> From: Julien Grall <jgrall@xxxxxxxxxx>
> 
> Since commit 54c4ae18d158 ("xen/arm32: head: Rework and document
> launch()"), the boot code is setting r12 but not read it.
> 
> So remove the two instructions setting r12 and update the documentation
> to show r12 has no specific purpose.
> 
> Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>

Cheers
Bertrand

> 
> ---
>    Changes in v2:
>        - Don't set r12.
> ---
> xen/arch/arm/arm32/head.S | 6 +-----
> 1 file changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
> index 13cfc837d39c..7a906167efca 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
> @@ -166,8 +166,6 @@ past_zImage:
> #endif
>         PRINT("- Boot CPU booting -\r\n")
> 
> -        mov   r12, #0                /* r12 := is_secondary_cpu */
> -
>         bl    check_cpu_mode
>         bl    cpu_init
>         bl    create_page_tables
> @@ -206,8 +204,6 @@ GLOBAL(init_secondary)
>         adr   r9, start              /* r9  := paddr (start) */
>         sub   r10, r9, r0            /* r10 := phys-offset */
> 
> -        mov   r12, #1                /* r12 := is_secondary_cpu */
> -
>         mrc   CP32(r1, MPIDR)
>         bic   r7, r1, #(~MPIDR_HWID_MASK) /* Mask out flags to get CPU ID */
> 
> -- 
> 2.32.0
> 
>