[PATCH] csky: Fix ABIv2 memcmp() s1 alignment check

[PATCH] csky: Fix ABIv2 memcmp() s1 alignment check

[Hanlin Song]

memcmp() saves the original s1 pointer in r3 and then clears r0 for the
return value. The following alignment check tests r0 instead of r3:

        mov     r3, r0
        movi    r0, 0
        ...
        andi    r13, r0, 3

As a result, the path for an unaligned s1 address is never taken, and
memcmp() may issue word loads from an unaligned s1 address.

Test r3 instead, which still holds the original s1 pointer.

Signed-off-by: Hanlin Song <pgeorge8929@gmail.com>
---
 arch/csky/abiv2/memcmp.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/csky/abiv2/memcmp.S b/arch/csky/abiv2/memcmp.S
index bf0d809f0..1c6ced74d 100644
--- a/arch/csky/abiv2/memcmp.S
+++ b/arch/csky/abiv2/memcmp.S
@@ -12,7 +12,7 @@ ENTRY(memcmp)
 	cmplti	r2, 4
 	bt	.L_compare_by_byte
 
-	andi	r13, r0, 3
+	andi	r13, r3, 3
 	movi	r19, 4
 
 	/* Test if s1 is not 4 bytes aligned.  */
-- 
2.25.1

Re: [PATCH] csky: Fix ABIv2 memcmp() s1 alignment check

[Hanlin Song]

Hi Guo Ren and C-SKY maintainers,

Gentle ping on this patch.

My understanding is that r3 holds the original s1 pointer after r0 is
cleared, so the alignment check should use r3 instead of r0. I also
tested this on a CK860f chip, and the patched version was faster in my
unaligned memcmp test.

I may be missing some C-SKY ABIv2 detail, so any feedback would be
appreciated.

Thanks,
Hanlin

Re: [PATCH] csky: Fix ABIv2 memcmp() s1 alignment check

[Guo Ren]

Hi Song,

On Mon, Jul 6, 2026 at 6:40 PM Hanlin Song <pgeorge8929@gmail.com> wrote:
>
> Hi Guo Ren and C-SKY maintainers,
>
> Gentle ping on this patch.
>
> My understanding is that r3 holds the original s1 pointer after r0 is
> cleared, so the alignment check should use r3 instead of r0. I also
> tested this on a CK860f chip, and the patched version was faster in my
> unaligned memcmp test.
>
> I may be missing some C-SKY ABIv2 detail, so any feedback would be
> appreciated.
>

Thanks for the patch, but this code is intentional. The CK810 and
CK860 support misaligned load/store in their microarchitecture, so the
alignment-check path is effectively dead code that exists only to keep
this asm code. It has been carried over unchanged from the very first.


-- 
Best Regards
 Guo Ren

Re: [PATCH] csky: Fix ABIv2 memcmp() s1 alignment check

[Hanlin Song]

Hi Guo Ren,

Thanks for the clarification.

Hanlin