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

* Al Viro <viro@ZenIV.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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