[PATCH] arm64: head: remove unnecessary instructions from __relocate_kernel

[PATCH] arm64: head: remove unnecessary instructions from __relocate_kernel

[Puranjay Mohan]

Formerly, we had to access the RELA and RELR tables via the kernel
mapping that was being relocated, and so deriving the start and end
addresses was done by loading __rela_offset in x9 and then adding the
actual virtual offset of the kernel to it.

d7bea550279d ("arm64: head: use relative references to the RELA and RELR
tables") changed this to load the entries via the ID map as we map the
entire kernel image via the ID map.

The two instructions for finding the actual virtual offset were left by
that commit, so remove them now as they are unnecessary and add runtime
overhead.

Fixes: d7bea550279d ("arm64: head: use relative references to the RELA and RELR tables")
Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
---
 arch/arm64/kernel/head.S | 2 --
 1 file changed, 2 deletions(-)

diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index cab7f91949d8..90db196f7c19 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -787,8 +787,6 @@ SYM_FUNC_START_LOCAL(__relocate_kernel)
 	 */
 	adr_l	x9, __rela_start
 	adr_l	x10, __rela_end
-	mov_q	x11, KIMAGE_VADDR		// default virtual offset
-	add	x11, x11, x23			// actual virtual offset
 
 0:	cmp	x9, x10
 	b.hs	1f

base-commit: 5ad3cb0ed525b80c7f66c32b49a68c1f3510bec9
-- 
2.42.0

Re: [PATCH] arm64: head: remove unnecessary instructions from __relocate_kernel

[Mark Rutland]

On Sat, Mar 02, 2024 at 02:52:10PM +0000, Puranjay Mohan wrote:
> Formerly, we had to access the RELA and RELR tables via the kernel
> mapping that was being relocated, and so deriving the start and end
> addresses was done by loading __rela_offset in x9 and then adding the
> actual virtual offset of the kernel to it.
> 
> d7bea550279d ("arm64: head: use relative references to the RELA and RELR
> tables") changed this to load the entries via the ID map as we map the
> entire kernel image via the ID map.
> 
> The two instructions for finding the actual virtual offset were left by
> that commit, so remove them now as they are unnecessary and add runtime
> overhead.

These instructions are already gone in linux-next; they're removed by commit:

  734958ef0b5497b1 ("arm64: head: move relocation handling to C code")

... so this patch isn't necessary.

> Fixes: d7bea550279d ("arm64: head: use relative references to the RELA and RELR tables")

As a heads-up for future patches, while this would be a cleanup it is not a
fix, and wouldn't need a fixes tag.

Mark.

> Signed-off-by: Puranjay Mohan <puranjay12@gmail.com>
> ---
>  arch/arm64/kernel/head.S | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
> index cab7f91949d8..90db196f7c19 100644
> --- a/arch/arm64/kernel/head.S
> +++ b/arch/arm64/kernel/head.S
> @@ -787,8 +787,6 @@ SYM_FUNC_START_LOCAL(__relocate_kernel)
>  	 */
>  	adr_l	x9, __rela_start
>  	adr_l	x10, __rela_end
> -	mov_q	x11, KIMAGE_VADDR		// default virtual offset
> -	add	x11, x11, x23			// actual virtual offset
>  
>  0:	cmp	x9, x10
>  	b.hs	1f
> 
> base-commit: 5ad3cb0ed525b80c7f66c32b49a68c1f3510bec9
> -- 
> 2.42.0
>