Re: A small issue with _GNU_SOURCE

[Corinna Vinschen <corinna-cygwin@cygwin.com>]

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On Feb 17 18:24, Jon TURNEY wrote:
> 
> Consider the following:
> 
> $ cat test.c
> #include <string.h>
> #include <stdlib.h>
> 
> int main()
> {
>  long long i = random();
>  return ffsll(i);
> }
> 
> ffsll() is a GNU extension and should be prototyped when _GNU_SOURCE is
> defined.
> 
> random() is in SUSv2 and requires _XOPEN_SOURCE=500
> 
> $ gcc test.c -Wall -ansi -D_XOPEN_SOURCE=700
> test.c: In function ‘main’:
> test.c:8:2: warning: implicit declaration of function ‘ffsll’
> 
> This is correct
> 
> $ gcc test.c -Wall -ansi -D_XOPEN_SOURCE=700 -D_GNU_SOURCE
> test.c: In function ‘main’:
> test.c:8:2: warning: implicit declaration of function ‘ffsll’
> 
> This looks like a problem with newlib's sys/cdefs.h.  _XOPEN_SOURCE causes
> _POSIX_C_SOURCE to be defined, which prevents _GNU_SOURCE from being
> considered.
> 
> $ gcc test.c -Wall -ansi -D_GNU_SOURCE
> test.c: In function ‘main’:
> test.c:7:2: warning: implicit declaration of function ‘random’
> 
> _GNU_SOURCE is supposed to imply some value of _XOPEN_SOURCE, but only
> actually turns on __XSI_VISIBLE.
> 
> The patch I wrote for cygwin's stdlib.h [1] explicitly checks _XOPEN_SOURCE.
> Should this be a check for XSI_VISIBLE? or should cdefs.h also define
> _XOPEN_SOURCE (and all the other feature test macros that _GNU_SOURCE is
> defined to be equivalent to)?

The check should be one for XSI_VISIBLE.  I'm not sure about cdefs.h,
though.  Maybe you want to ask the question on the newlib ML?  I'll
look into it tomorrow.


Thanks,
Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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