Re: rc4-mmotm1110 - Another build error

[Valdis.Kletnieks@vt.edu]

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On Mon, 10 Nov 2008 19:43:53 PST, Andrew Morton said:
> On Mon, 10 Nov 2008 22:20:33 -0500 Valdis.Kletnieks@vt.edu wrote:
> 
> > gcc --version says:
> > gcc (GCC) 4.3.2 20081105 (Red Hat 4.3.2-7)
> > 
> > ka-blam number 2:
> > 
> >   CC      kernel/audit.o
> > In file included from include/net/dst.h:15,
> >                  from include/net/sock.h:57,
> >                  from kernel/audit.c:54:
> > include/net/neighbour.h:114: error: braced-group within expression allowed 
only inside a function
> > make[1]: *** [kernel/audit.o] Error 1
> > 
> > I'm placing bets on patches/align-avoid-evaluating-its-argument-twice.patch
> > 
> > Yep, revert that patch, and audit.o compiles again.
> > 
> 
> I hadn't got around to testing that one yet.
> 
> So ug.  ALIGN() is used in array sizing and hence has to be a
> compile-time thing.  But ALIGN(foo, bar()) will call bar() twice.
> 
> Now how do we fix that?

Can we abuse __builtin_constant_p somehow?  Maybe we can make a definition
something like:

#define __align_mask(x,mask) (
	__builtin_constant_p(mask) ? {
		(((x)+(mask))&~(mask)) :
		{              \
		      typeof(mask) __mask = mask;             \
		       (((x) + __mask) & ~__mask);             \
		}
	})

If it's a compile-time constant, it's safe to evaluate mask twice.
And if it's *not* a constant, it shouldn't be used for sizing arrays
in open code.  And if it's an array local to a procedure, it probably
should be kmalloc()'ed instead.


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