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

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Date:	Sun, 24 Jun 2007 11:04:57 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Al Viro <viro@....linux.org.uk>
cc:	linux-kernel@...r.kernel.org, linux-sparse@...r.kernel.org
Subject: Re: [PATCH 16/16] fix handling of integer constant expressions



On Sun, 24 Jun 2007, Al Viro wrote:
> 
> Heh...  The first catches are lovely:
>                  struct fxsrAlignAssert {
>                          int _:!(offsetof(struct task_struct,
>                                          thread.i387.fxsave) & 15);

Ok, that's a bit odd.

> 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",

On the other hand, this one really does seem to be "nice".

I don't think it's a misfeature to be able to do "obvious compile-time 
constant optimizations" on initializer indexes. The bitfield size thing in 
some ways does do the same thing - it's clearly _odd_, but if I had my  
choice, I'd prefer a language that allows it over one that doesn't.

> 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.

I agree that it's obviously not "valid C", but I don't agree that it's not 
remotely sane. Why not allow that extension? 

		Linus
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