linux-kernel - Re: [PATCH]: Fix ALIGN() macro

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Date:	Sat, 23 Sep 2006 16:42:47 -0400
From:	Kyle Moffett <mrmacman_g4@....com>
To:	Kyle Moffett <mrmacman_g4@....com>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	David Miller <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, torvalds@...l.org
Subject: Re: [PATCH]: Fix ALIGN() macro

On Sep 23, 2006, at 16:36:33, Kyle Moffett wrote:
> On Sep 23, 2006, at 10:40:41, Herbert Xu wrote:
>> diff --git a/crypto/hmac.c b/crypto/hmac.c
>> index f403b69..d52b234 100644
>> --- a/crypto/hmac.c
>> +++ b/crypto/hmac.c
>> @@ -98,7 +98,7 @@ static int hmac_init(struct hash_desc *p
>>  	sg_set_buf(&tmp, ipad, bs);
>>
>>  	return unlikely(crypto_hash_init(&desc)) ?:
>> -	       crypto_hash_update(&desc, &tmp, 1);
>> +	       crypto_hash_update(&desc, &tmp, bs);
>>  }
>>
>>  static int hmac_update(struct hash_desc *pdesc,
>
> Quick question:  does "crypto_hash_init()" ever return anything  
> other than 0 or 1?  If so this is a subtle bug, as "unlikely()" is  
> implemented like this:
>
> # define unlikely(x) __builtin_expect(!!(x), 0)
>
> IMO any usage of likely/unlikely other than if(unlikely()), if 
> (likely()) is probably a bug.

With a bit more contemplation, I think this is one place where (if  
the compiler or sparse are cooperative) we should really look at the  
_Bool type or similar.  If we could cast likely()/unlikely() to  
return (_Bool), then these sorts of problems would be caught at  
compile time, and likewise for other functions which return boolean  
values.

Cheers,
Kyle Moffett

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