linux-kernel - Re: [patch] crypto: sha256-mb - cleanup a || vs

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Message-ID: <57750665.7000703@bfs.de>
Date:	Thu, 30 Jun 2016 13:45:41 +0200
From:	walter harms <wharms@....de>
To:	Joe Perches <joe@...ches.com>
CC:	Dan Carpenter <dan.carpenter@...cle.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	"David S. Miller" <davem@...emloft.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Megha Dey <megha.dey@...el.com>,
	"Wang, Rui Y" <rui.y.wang@...el.com>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Xiaodong Liu <xiaodong.liu@...el.com>,
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-janitors@...r.kernel.org
Subject: Re: [patch] crypto: sha256-mb - cleanup a || vs | typo



Am 30.06.2016 13:16, schrieb Joe Perches:
> On Thu, 2016-06-30 at 10:50 +0300, Dan Carpenter wrote:
>> On Wed, Jun 29, 2016 at 10:05:53AM -0700, H. Peter Anvin wrote:
>>> On 06/29/16 07:42, Dan Carpenter wrote:
>>>>>> and | behave basically the same here but || is intended.  It causes a
>>>> static checker warning to mix up bitwise and logical operations.
>>>>
>>>> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
>>>>
>>>> diff --git a/arch/x86/crypto/sha256-mb/sha256_mb.c b/arch/x86/crypto/sha256-mb/sha256_mb.c
> []
>>>> @@ -299,7 +299,7 @@ static struct sha256_hash_ctx *sha256_ctx_mgr_submit(struct sha256_ctx_mgr *mgr,
>>>>  	 * Or if the user's buffer contains less than a whole block,
>>>>  	 * append as much as possible to the extra block.
>>>>  	 */
>>>> -	if ((ctx->partial_block_buffer_length) | (len < SHA256_BLOCK_SIZE)) {
>>>> +	if ((ctx->partial_block_buffer_length) || (len < SHA256_BLOCK_SIZE)) {
>>>>  		/* Compute how many bytes to copy from user buffer into
>>>>  		 * extra block
>>>>  		 */
>>>>
>>> As far as I know the | was an intentional optimization, so you may way
>>> to look at the generated code.
>> I know how the rules work.  I just thought it looked more like a typo
>> than an optimization.  It's normally a typo.  It's hard to tell the
>> intent.
> 
> The compiler could potentially emit the same code when
> optimizing but at least gcc 5.3 doesn't.
> 
> It's probably useful to add a comment for the specific intent
> here rather than change a potentially useful static checker.
> 

perhaps we can agree not to play tricks with a compiler.
Everything may be true for a certain version of CC but the next compiler is different.

just my 2 cents,
 wh