netdev - Re: [PATCH net-next 5/5] net: sctp: fix incorrect type in gfp initializer

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Date:	Wed, 11 Jun 2014 17:09:32 +0200
From:	Daniel Borkmann <dborkman@...hat.com>
To:	David Laight <David.Laight@...LAB.COM>
CC:	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-sctp@...r.kernel.org" <linux-sctp@...r.kernel.org>,
	Tejun Heo <tj@...nel.org>
Subject: Re: [PATCH net-next 5/5] net: sctp: fix incorrect type in gfp initializer

On 06/11/2014 04:55 PM, David Laight wrote:
> From: Daniel Borkmann
>> This fixes the following sparse warning:
>>
>>    net/sctp/associola.c:1556:29: warning: incorrect type in initializer (different base types)
>>    net/sctp/associola.c:1556:29:    expected bool [unsigned] [usertype] preload
>>    net/sctp/associola.c:1556:29:    got restricted gfp_t
> ...
>> --- a/net/sctp/associola.c
>> +++ b/net/sctp/associola.c
>> @@ -1591,7 +1591,7 @@ int sctp_assoc_lookup_laddr(struct sctp_association *asoc,
>>   /* Set an association id for a given association */
>>   int sctp_assoc_set_id(struct sctp_association *asoc, gfp_t gfp)
>>   {
>> -	bool preload = gfp & __GFP_WAIT;
>> +	bool preload = !!(gfp & __GFP_WAIT);
>>   	int ret;
>>
>>   	/* If the id is already assigned, keep it. */
>> --
>
> I was wondering if the compiler still manages to optimise this in a
> manner that avoids actually calculating the boolean value...
>
> So I disassembled the compilation I just did of the old code (gcc 4.7.3).
> The object code looks strange.
> I think that idr_preload_end() must be an empty inline function.

Cc'ing Tejun. ;-)

> The compiler has duplicated the code between the two 'if (preload)'
> clauses (to avoid the conditional test), and the failed to tail
> merge everything in the latter stages.
> I suspect that an empty '#define' would generate smaller code.
>
> 	David
>
>
>
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