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

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Date:	Sun, 24 Jun 2007 18:47:32 +0100
From:	Al Viro <viro@....linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-sparse@...r.kernel.org
Subject: Re: [PATCH 16/16] fix handling of integer constant expressions

On Sun, Jun 24, 2007 at 09:05:51AM +0100, Al Viro wrote:
> 
> Hopefully correct handling of integer constant expressions.  Please, review.

Heh...  The first catches are lovely:
                 struct fxsrAlignAssert {
                         int _:!(offsetof(struct task_struct,
                                         thread.i387.fxsave) & 15);
                 };
as an idiotic way to do BUILD_BUG() and
#define _IOC_TYPECHECK(t) \
        ((sizeof(t) == sizeof(t[1]) && \
          sizeof(t) < (1 << _IOC_SIZEBITS)) ? \
          sizeof(t) : __invalid_size_argument_for_IOC)
poisoning _IOW() et.al., so those who do something like

static const char *v4l1_ioctls[] = {
        [_IOC_NR(VIDIOCGCAP)]       = "VIDIOCGCAP",

run into trouble.  The former is "tell jbeulich to cut down on crack",
but the latter...  Probably ought to be
#define _IOC_TYPECHECK(t) \
        (sizeof(t) + BUILD_BUG_ON_ZERO(sizeof(t) == sizeof(t[1]) && \
          sizeof(t) < (1 << _IOC_SIZEBITS)))

Objections?  The only reason that doesn't break gcc to hell and back is
that gcc has unfixed bugs in that area.  It certainly is not a valid C
or even a remotely sane one.
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