xen/arm32: head: Update the documentation for register r12

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

Posted by Julien Grall 2 years, 2 months ago

From: Julien Grall <jgrall@amazon.com>

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@amazon.com>
---
 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
-- 
2.32.0

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

Posted by Michal Orzel 2 years, 2 months ago

Hi Julien,

On 28.02.2022 11:11, Julien Grall wrote:
> From: Julien Grall <jgrall@amazon.com>
> 
> 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@amazon.com>
> ---
>  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

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

Posted by Julien Grall 2 years, 2 months ago


On 28/02/2022 13:04, Michal Orzel wrote:
> Hi Julien,

Hi Michal,

Thank you for the review.

> 
> On 28.02.2022 11:11, Julien Grall wrote:
>> From: Julien Grall <jgrall@amazon.com>
>>
>> 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@amazon.com>
>> ---
>>   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)

We don't need them. I will drop them and respin the patch.

Cheers,

-- 
Julien Grall