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Subject: Re: Inconsistency with coreutils: _Static_assert()
From: Denis Excoffier <cygwin AT Denis-Excoffier DOT org>
In-Reply-To: <20130522085310.GV2406@calimero.vinschen.de>
Date: Wed, 22 May 2013 18:17:18 +0200
Message-Id: <7E8B4273-EEA0-4E04-B1F5-B097290EE0B4@Denis-Excoffier.org>
References: <97bfaa4aab229c706de5732905c96b44 AT denis-excoffier DOT org> <20130521160846 DOT GP2406 AT calimero DOT vinschen DOT de> <4DB22033-B92B-45C0-81F3-72D10CBDA8C0 AT Denis-Excoffier DOT org> <20130522085310 DOT GV2406 AT calimero DOT vinschen DOT de>
To: cygwin AT cygwin DOT com
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On 2013-05-22 10:53, Corinna Vinschen wrote:
> On May 21 21:25, Denis Excoffier wrote:
>> On 2013-05-21 18:08, Corinna Vinschen wrote:
>>> On May 21 17:59, Denis Excoffier wrote:
>>>> I have narrowed the problem down to /usr/include/sys/cdefs.h, where
>>>> (line 271) you have _Static_assert defined:
>>>> #define _Static_assert(x, y)  __Static_assert(x, __COUNTER__)
>>>> 
>>>> This definition occurs even under GCC 4.6.0 (and later) where
>>>> _Static_assert() indeed works. As a consequence, it no longer works as
>>>> expected in coreutils-8.21/lib/verify.h (lines 24 and 181).
>>> 
>>> Sorry, but I don't grok this sentence.  Since the cdefs.h version
>>> works as expected, it does not work in coreutils' verify.h?  Who
>>> exactly is wrong, cdefs.h or verify.h?  And *what* exactly is wrong
>>> with the definition?
>> As soon as you are under GCC >= 4.6, _Static_assert() works directly,
>> hence line 271 of cdefs.h is not needed. More than that, when you
>> (re)define it to something else, the original behavior is no longer
>> available, and e.g. coreutils (that is "verify.h") fails to compile.
>> 
>> You should (IMHO) change cdefs.h in order to read (as far as only
>> _Static_assert is concerned):
>> 
>> #if defined(__cplusplus) && __cplusplus >= 201103L
>> . . . (same) . . .
>> #elif defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L
>> . . . (same) . . .
>> #elif (4 < __GNUC__ || (__GNUC__ == 4 && 6 <= __GNUC_MINOR__)) && !defined __cplusplus
>> /* Do nothing: _Static_assert() works as per C11 */
>> #else
>> /* Not supported.  Implement them using our versions. */
>> . . . (same) . . .
>> #endif
>> 
>> I don't really know if the lines above correctly take care of
>> __STRICT_ANSI__ but you get the idea.
> 
> I tried it, and it looks like the definition of _Static_assert in gcc >=
> 4.6 is independent of __STRICT_ANSI__.
> 
> Can you test this patch to sys/cdefs.h, please?
> 
> Index: sys/cdefs.h
> ===================================================================
> RCS file: /cvs/src/src/newlib/libc/include/sys/cdefs.h,v
> retrieving revision 1.4
> diff -u -p -r1.4 cdefs.h
> --- sys/cdefs.h	22 Apr 2013 10:28:05 -0000	1.4
> +++ sys/cdefs.h	22 May 2013 08:52:51 -0000
> @@ -267,7 +267,9 @@
> #define	_Alignof(x)		__alignof(x)
> #define	_Noreturn		__dead2
> #define	_Thread_local		__thread
> -#ifdef __COUNTER__
> +#if __GNUC_PREREQ__(4, 6) && !defined(__cplusplus)
> +/*  Do nothing: _Static_assert() works as per C11 */
> +#elif defined(__COUNTER__)
> #define	_Static_assert(x, y)	__Static_assert(x, __COUNTER__)
> #define	__Static_assert(x, y)	___Static_assert(x, y)
> #define	___Static_assert(x, y)	typedef char __assert_ ## y[(x) ? 1 : -1]
> 
This patch works perfectly. Thank you.

Denis Excoffier.


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