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

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Message-Id: <b739fb9ad6e68bfe5d2a4b839abc8ea4@kernel.crashing.org>
Date:	Sun, 24 Jun 2007 20:18:52 +0200
From:	Segher Boessenkool <segher@...nel.crashing.org>
To:	Al Viro <viro@....linux.org.uk>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-sparse@...r.kernel.org
Subject: Re: [PATCH 16/16] fix handling of integer constant expressions

>> 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);
>                  };

That's...  wow?

> #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 only reason that doesn't break gcc to hell and back is
> that gcc has unfixed bugs in that area.

If I understand correctly what bugs you are talking about,
most (all?) of those were solved in the dark ages already
(i.e., the 3.x series).

> It certainly is not a valid C

Why not?  Nothing in the C standard says all your externs
have to be defined in some other translation unit you link
with AFAIK.

> or even a remotely sane one.

It's unusual at least :-)


Segher

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