Re: [PATCH 16/16] fix handling of integer constant expressions

[Al Viro <viro@ftp.linux.org.uk>]

On Sun, Jun 24, 2007 at 08:07:10PM +0200, Arnd Bergmann wrote:
> One minor issue though:
> While BUILD_BUG_ON and a few other macros in linux/kernel.h are currently
> exported to user space, I would think that they should really be hidden
> in #ifdef __KERNEL__, which means that we also need something like
> 
> #ifdef __KERNEL__
> #define _IOC_TYPECHECK(t) \
>         (sizeof(t) + BUILD_BUG_ON_ZERO(sizeof(t) == sizeof(t[1]) && \
>           sizeof(t) < (1 << _IOC_SIZEBITS)))
> #else
> #define _IOC_TYPECHECK(t) sizeof(t)
> #endif

Point, but then we might want to export the damn thing in properly
named version (i.e. put it into __.... reserved namespace).  It
doesn't depend on anything kernel-specific...

FWIW, the current version suffers from similar problem - it's outside
of __KERNEL__ in userland-exported header and it can lead to breakage
when included in build by something other than gcc...