Re: [PATCH] powerpc/32: fix csum_partial_copy_generic()

On Mon, Aug 01, 2016 at 03:45:59PM +0200, Christophe Leroy wrote:

quoted

quoted

--- a/arch/powerpc/lib/checksum_32.S
+++ b/arch/powerpc/lib/checksum_32.S

@@ -127,7 +127,8 @@ _GLOBAL(csum_partial_copy_generic)

	stw	r7,12(r1)
	stw	r8,8(r1)

-	andi.	r0,r4,1			/* is destination address even ? */
+	rlwinm	r0,r4,3,0x8		/* is destination address even ? */
+	rlwnm	r6,r6,r0,0,31		/* swap bytes for odd destination */
	cmplwi	cr7,r0,0
	addic	r12,r6,0
	addi	r6,r4,-4

That does not "swap bytes"; it shifts the word up by 8 bits, instead.
That may or may not do what is intended.

Indeed it does what is intended, similar to what is done at the end of 
the function:

	...
	beqlr+	cr7
	rlwinm	r3,r3,8,0,31	/* swap bytes for odd destination */
 	blr

Should I fix the (both) comment(s) ?

It's quite confusing comment, so yes please.  The code is hard enough to
understand as is!


Segher