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

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Date:	Wed, 11 Jun 2014 14:55:09 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Daniel Borkmann' <dborkman@...hat.com>,
	"davem@...emloft.net" <davem@...emloft.net>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-sctp@...r.kernel.org" <linux-sctp@...r.kernel.org>
Subject: RE: [PATCH net-next 5/5] net: sctp: fix incorrect type in gfp
 initializer

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.
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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