Re: [Xen-devel] [PATCH 2/2] xen/arm64: use shift operator

[Peng Fan <van.freenix@xxxxxxxxx>]

Hi Julien,

On Wed, Apr 20, 2016 at 03:44:09PM +0100, Julien Grall wrote:
>Hello Peng,
>
>On 20/04/16 14:54, Peng Fan wrote:
>>Use shift operator, but not muliplication.
>>No function change.
>
>Why? The compiler will calculate the address at compilation time.

Yeah. The compiler will do this. I just think in asm, we rarely use
multiplication. In this file, there is "cmp   x1, #(LPAE_ENTRIES<<3)",
here use shift operator but not multiplication.

Thanks,
Peng.

>
>Regards,
>
>>Signed-off-by: Peng Fan <van.freenix@xxxxxxxxx>
>>Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
>>Cc: Julien Grall <julien.grall@xxxxxxx>
>>---
>>  xen/arch/arm/arm64/head.S | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>>diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
>>index 05e3db0..ad6e593 100644
>>--- a/xen/arch/arm/arm64/head.S
>>+++ b/xen/arch/arm/arm64/head.S
>>@@ -524,7 +524,7 @@ paging:
>>          lsl   x2, x2, #THIRD_SHIFT   /* 4K aligned paddr of UART */
>>          mov   x3, #PT_DEV_L3
>>          orr   x2, x2, x3             /* x2 := 4K dev map including UART */
>>-        str   x2, [x1, #(FIXMAP_CONSOLE*8)] /* Map it in the first fixmap's 
>>slot */
>>+        str   x2, [x1, #(FIXMAP_CONSOLE << 3)] /* Map it in the first 
>>fixmap's slot */
>>  1:
>>
>>          /* Map fixmap into boot_second */
>>
>
>-- 
>Julien Grall

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel