linux-kernel - Re: Linux Kernel include files

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Message-ID: <20070627154046.GN1094@stusta.de>
Date:	Wed, 27 Jun 2007 17:40:46 +0200
From:	Adrian Bunk <bunk@...sta.de>
To:	Kyle Moffett <mrmacman_g4@....com>
Cc:	David Woodhouse <dwmw2@...radead.org>,
	Joerg Schilling <Joerg.Schilling@...us.fraunhofer.de>,
	david@...g.hm, LKML Kernel <linux-kernel@...r.kernel.org>
Subject: Re: Linux Kernel include files

On Tue, Jun 26, 2007 at 09:32:39PM -0400, Kyle Moffett wrote:
> On Jun 22, 2007, at 11:00:38, Adrian Bunk wrote:
>> It would certainly help if Joerg would tell what exactly breaks, but I 
>> spot one likely problem in include/asm-i386/types.h:
>>
>> #if defined(__GNUC__) && !defined(__STRICT_ANSI__)
>> typedef __signed__ long long __s64;
>> typedef unsigned long long __u64;
>> #endif
>>
>> It might make sense to remove the #if and simply require that a C compiler 
>> under Linux must know about the C99 "long long"?
>
> Gah, this particular topic and a few other similar header-compatibility 
> ones show up once a month on LKML; I should probably just make a patch to 
> fix all the types.h files and be done with it.  The proper solution is 
> this:
>
> # if __STDC_VERSION__ >= 19901L
> typedef   signed long long __s64;
> typedef unsigned long long __u64;
> # elif defined(__GNUC__)
> __extension__ typedef   signed long long __s64;
> __extension__ typedef unsigned long long __u64;
> # else
> #  error "Your compiler doesn't support long long (IOW: It sucks).  Please 
> get a new one"

This part is wrong.

gcc supported "long long" before C99 existed.
And Joerg said the Sun cc supported "long long" before gcc did.

> # endif
>
> That way if you have any kind of vaguely-long-long-compatible compiler then 
> it will work, and otherwise you'll get a nice useful error message.

No, consider a pre-C99 gcc version that supports "long long".

> It 
> also makes sure that GCC doesn't spew warnings/errors when in c89-pedantic 
> mode.  The "__extension__" keyword is designed for use in implementation 
> header files which want to use GCC-isms unconditionally.

That's a good point I missed.

What about:

#if defined(__GNUC__) && __STDC_VERSION__ < 19901L
__extension__ typedef   signed long long __s64;
__extension__ typedef unsigned long long __u64;
#else
typedef   signed long long __s64;
typedef unsigned long long __u64;
#endif

> Cheers,
> Kyle Moffett

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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