Re: Ensuring posix-ness

[Eric Blake]

On 09/07/2011 10:33 PM, Bruno Haible wrote:
> > The crypt example is particularly annoying, as without _XOPEN_SOURCE
> > defined it's not defined, even though POSIX_VERSION is>= 200112L, and
> > it's in that version of POSIX (of course, that's a glibc bug

Setting _POSIX_C_SOURCE to 200809L _should_ automatically turn on 
_XOPEN_SOURCE of 700. (Setting it to 200112L sets _XOPEN_SOURCE to 600, 
but POSIX 2001 is 10 years old, and you're better off catering to POSIX 
2008 these days).

> $ cat foo.c
> #define _POSIX_C_SOURCE 200112L
> #include<unistd.h>
> $ gcc -E foo.c | grep crypt

Glibc bug.  XSI shading means that a non-XSI implementation need not 
have crypt by default, but glibc is an XSI implementation, so requesting 
compliance with POSIX 2008 means that crypt() should be visible in 
<unistd.h>.  There's no feature macro needed to turn on XSI functions - 
either you have an XSI system and they are all available by default, or 
you do not have an XSI system (usually embedded systems) and the system 
documents that it is not provide XSI.

> Indeed crypt() is on POSIX:2001
> <http://pubs.opengroup.org/onlinepubs/009604499/functions/crypt.html>.
> But it is marked as [XSI]. I don't know whether that implies that glibc is
> right in hiding the declaration, or it should enable it?

crypt() is also in POSIX 2008, and the bug still persists:

$ printf '#define _POSIX_C_SOURCE 200809L\n#include <unistd.h>\n' \
  | gcc -E - | grep crypt

Would you care to raise a bug report against glibc?

> > Have I missed anything, or is this a gap in gnulib's coverage?

We could add a gnulib crypt module that exposes the declaration by 
default (basically, a stub module that depends on extensions, since the 
use of the extensions module is also sufficient to convince glibc to 
declare crypt).

> Certainly the fact that crypt() is not defined by default could be mentioned
> in doc/posix-functions/crypt.texi.
>
> Bruno

--
Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org