linux-kernel - Re: [PATCH] powerpc/32: fix csum_partial_copy

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Date:	Mon, 1 Aug 2016 15:45:59 +0200
From:	Christophe Leroy <christophe.leroy@....fr>
To:	Segher Boessenkool <segher@...nel.crashing.org>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Scott Wood <oss@...error.net>, antoine.blangy@....fr,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] powerpc/32: fix csum_partial_copy_generic()



Le 01/08/2016 à 15:15, Segher Boessenkool a écrit :
> On Mon, Aug 01, 2016 at 02:56:05PM +0200, Christophe Leroy wrote:
>> --- 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) ?

Christophe