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SubjectRe: rc4-mmotm1110 - Another build error
On Tue, 11 Nov 2008 14:04:57 -0500
Valdis.Kletnieks@vt.edu wrote:

> 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.

This seems to compile:

int y;
char x[__builtin_constant_p(1) ? 42 : y + 1];

so yes, that might work. For this gcc version. However I suspect that
it would blow up on us. We keep on having problems with the
__builtin_constant_p() in kmalloc() doing wrong things (with gcc-3.2.x,
iirc).

It'd be worth trying though.

DIV_ROUND_UP() and roundup() are busted too.


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