linux-kernel - Re: [PATCH] serial/atmel_serial: Fix another fallout of the change to BUILD_BUG

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Message-Id: <200910200102.30478.rusty@rustcorp.com.au>
Date:	Tue, 20 Oct 2009 01:02:29 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	"Jan Beulich" <JBeulich@...ell.com>
Cc:	"Haavard Skinnemoen" <haavard.skinnemoen@...el.com>,
	"Haavard Skinnemoen" <hskinnemoen@...el.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Alan Cox" <alan@...ux.intel.com>,
	linux-arm-kernel@...ts.infradead.org,
	u.kleine-koenig@...gutronix.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] serial/atmel_serial: Fix another fallout of the change to BUILD_BUG_ON

On Mon, 19 Oct 2009 06:49:40 pm Jan Beulich wrote:
> >>> Rusty Russell <rusty@...tcorp.com.au> 19.10.09 08:08 >>>
> >How's this?  It's not quite valid C, but it "works":
> 
> But that's not what you proposed initially, i.e. generating a link time
> error if a compile time error can't be generated (and only if even a link
> time error isn't possible, a run time one should be forced).

Yeah, this was cleverer.  A compile time is nicer than link time.  And this
is *actually* what I want: a compile fail if the compiler knows enough, runtime
otherwise.

> And btw., why do you think this isn't valid C?

>From my glance at ISO C, non-positive sized variable length arrays are
invalid.  gcc here seems to give the expected results (eg. sizeof gives
a negative result).

Cheers,
Rusty.
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