linux-kernel - Re: Nasal demons in preprocessor use (Re: [PATCH] test-suite: new preprocessor test case)

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Date:	Thu, 19 Mar 2009 20:27:58 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Vegard Nossum <vegard.nossum@...il.com>,
	Christopher Li <sparse@...isli.org>,
	linux-sparse@...r.kernel.org, Hannes Eder <hannes@...neseder.net>,
	linux-kernel@...r.kernel.org
Subject: Re: Nasal demons in preprocessor use (Re: [PATCH] test-suite: new
	preprocessor test case)


* Al Viro <viro@...IV.linux.org.uk> wrote:

> On Thu, Mar 19, 2009 at 07:51:22PM +0100, Hannes Eder wrote:
> > When currently running sparse agains the current linux-next tree, a
> > lot of checks produce error messages like this:
> > 
> > include/linux/skbuff.h:381:9: error: expected preprocessor identifier
> 
> Cute.  If anything, this kmemcheck_define_bitfield stuff needs to be moved
> inside the ifdefs.
> 
> Folks, this is not a valid C, period.  And no, there's no promise 
> that gcc won't change its behaviour on such constructs whenever 
> they feel like that.
> 
> Preprocessor directives do not belong in argument lists.  Not 
> #ifdef, not #define, not #include; this is undefined behaviour.

Agreed.

Vegard, it's this bit:

        kmemcheck_define_bitfield(flags2, {
#ifdef CONFIG_IPV6_NDISC_NODETYPE
                __u8                    ndisc_nodetype:2;
#endif
#if defined(CONFIG_MAC80211) || defined(CONFIG_MAC80211_MODULE)
                __u8                    do_not_encrypt:1;
                __u8                    requeue:1;
#endif
        });

	Ingo
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