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Re: Define _POSIX_SOURCE in cygwin's features.h?
On Thu, Jan 12, 2006 at 07:06:43PM -0000, Dave Korn wrote:
>Christopher Faylor wrote:
>>If I could easily make cygwin behave exactly the same way so that a
>>buffer overrun that worked on linux went undetected on cygwin, too, I'd
>>do that? If there was some linker option to ensure that, I'd use it.
>>
>>The point of cygwin isn't that it is a place where you find bugs which
>>you should have fixed on linux. Every place where there is a barrier
>>to porting a program from linux to cygwin is YA opportunity for someone
>>to give up in disgust or (maybe worse) send a "I get compile error"
>>message here.
>>
>>But, I understand your opinion on the matter.
>
>I understand yours too, and it's equally valid. I'm curious why
>someone's application would want to test _POSIX_SOURCE - it should be
>the app that sets it or not and it should just know. But if they've
>handed the responsibility to auto* to determine when to use it, and
>auto* decides YES for Linux, then I agree it should certainly DTST on
>Cygwin.
This particular application was ircd. It was testing _POSIX_SOURCE (and
a few other defines) to determine whether it should use setsid or a
two-argument version of setpgrp, e.g.:
#ifdef _POSIX_SOURCE
setsid ();
#else
setpgr(..., ...);
#endif
Again, I should have tested what I was talking about. It turns out that
_POSIX_SOURCE *is* turned on by default on in glibc regardless of
whether you define _GNU_SOURCE or not. So that would explain why this
application built.
Apparently _POSIX_SOURCE is turned on by this segment of features.h:
#if ((!defined __STRICT_ANSI__ || (_XOPEN_SOURCE - 0) >= 500) && \
!defined _POSIX_SOURCE && !defined _POSIX_C_SOURCE)
# define _POSIX_SOURCE 1
# if defined _XOPEN_SOURCE && (_XOPEN_SOURCE - 0) < 500
# define _POSIX_C_SOURCE 2
# else
# define _POSIX_C_SOURCE 199506L
# endif
#endif
The application in question *could* have done things differently but
there is no way that this irc user would have been capable of making any
changes to accomplish this. I was wondering if anyone had specific
examples where defining _POSIX_SOURCE would help or hurt existing
applications. I understand that it wouldn't be as simple as just
defining _POSIX_SOURCE in a header and then walking away but I'm willing
to look into fixing up the cygwin header files to "do the right thing"
(for all I know, they already do) when _POSIX_SOURCE is defined.
cgf
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