linux-kernel - Re: [PATCH v2] kconfig/kbuild: define _POSIX_C

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Date:	Tue, 19 Apr 2011 11:54:19 +0200
From:	Michal Marek <mmarek@...e.cz>
To:	Valentin Ochs <a@....de>
Cc:	Roman Zippel <zippel@...ux-m68k.org>, trivial@...nel.org,
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] kconfig/kbuild: define _POSIX_C_SOURCE

On 10.4.2011 16:31, Valentin Ochs wrote:
> On Sat, Apr 09, 2011 at 11:34:00PM -0400, Arnaud Lacombe wrote:
>> On Sat, Apr 9, 2011 at 10:09 PM, Valentin Ochs <a@....de> wrote:
>>> The three patched files use PATH_MAX without defining the required
>>> _POSIX_C_SOURCE feature test macro.  This prevents compilation with the
>>> musl libc.  The patch applies to 2.6.38.2.
>>>
>>> Changes since v1:
>>>  - fix scripts/kconfig/lex.zconf.c_shipped
>> this file is autogenerated from zconf.l, which should be updated as
>> well. I'm not sure how you searched for PATH_MAX, but you're still
>> missing `confdata.c' and `nconf.c'.

Yes, please fix the bison parser and run make GENERATE_PARSER=1
menuconfig to update the *_shipped files.


>> I had a quick look to different libc implementation, glibc and uClibc
>> default to _POSIX_C_SOURCE == 200112L, FreeBSD >8.0 defaults to
>> 200809L for >8.0, FreeBSD 7.x to 200112L.
> 
> I got the value I used from the Open Group System Interfaces
> specification, but the musl author said that 200112L would be fine too.

I suggest you use 200112L, so that it is a nop for glibc/uClibc builds.
Please also accompany it with a /* for PATH_MAX */ comment or so.

> 
>> None of these seems to requires _POSIX_C_SOURCE to define PATH_MAX, so
>> I'm not certain of the requirement of the change.
> 
> While I don't want to appear like a language lawyer, the specification
> says that 'all symbols required by POSIX.1-2008 to appear when the
> header is included shall be made visible' when an application defines
> _POSIX_C_SOURCE. I guess the musl author interprets that as 'if you
> don't define the feature test macros, you're not getting PATH_MAX.' This
> does not seem to be incorrect behaviour to me.

While I don't completely understand the motivation for such
super-pedantic libc implementation, the fact is that POSIX says one
should define this macro, so let's define it, it does not hurt us.

Michal
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