[Toybox] _GNU_SOURCE definition problem

[Georgi Chorbadzhiyski]

On 3/9/12 7:47 PM, Rob Landley wrote:
> On 03/09/2012 08:14 AM, Georgi Chorbadzhiyski wrote:
>> Removing _GNU_SOURCE breaks toys/unshare compilation.
>
> Building under what?
>
> In /usr/include/features.h:
>
> #if defined _BSD_SOURCE || defined _SVID_SOURCE
> # define __USE_MISC     1
> #endif
>
> sched.h includes bits/sched.h, and in /usr/include/bits/sched.h the
> CLONE_NEW* defines are all in #ifdef __USE_MISC
>
> So... works for me?  (Just did a test build...)

 From /usr/include/bits/sched.h [1] on my desktop (glibc-2.14.1, slack-current)

#ifdef __USE_GNU

...
# define CLONE_NEWUTS   0x04000000      /* New utsname group.  */
# define CLONE_NEWIPC   0x08000000      /* New ipcs.  */
# define CLONE_NEWUSER  0x10000000      /* New user namespace.  */
# define CLONE_NEWPID   0x20000000      /* New pid namespace.  */
# define CLONE_NEWNET   0x40000000      /* New network namespace.  */
# define CLONE_IO       0x80000000      /* Clone I/O context.  */
...

#endif

...

#ifdef __USE_GNU
/* Clone current process.  */
extern int clone (int (*__fn) (void *__arg), void *__child_stack,
                   int __flags, void *__arg, ...) __THROW;

/* Unshare the specified resources.  */
extern int unshare (int __flags) __THROW;

...

#endif

Resulting in:

toys/unshare.c: In function ‘unshare_main’:
toys/unshare.c:32:20: error: ‘CLONE_NEWNS’ undeclared (first use in this function)
toys/unshare.c:32:20: note: each undeclared identifier is reported only once for each function it appears in
toys/unshare.c:32:33: error: ‘CLONE_NEWUTS’ undeclared (first use in this function)
toys/unshare.c:32:47: error: ‘CLONE_NEWIPC’ undeclared (first use in this function)
toys/unshare.c:32:61: error: ‘CLONE_NEWNET’ undeclared (first use in this function)
toys/unshare.c:40:2: warning: implicit declaration of function ‘unshare’ [-Wimplicit-function-declaration]
make: *** [toybox] Error 1

glibc insists that this Linux only functionality is behind __USE_GNU
which is declared in features.h if _GNU_SOURCE is declared [2].

Beautiful :(

[1]: http://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/bits/sched.h
[2]: http://sourceware.org/git/?p=glibc.git;a=blob;f=include/features.h;hb=HEAD

-- 
Georgi Chorbadzhiyski
http://georgi.unixsol.org/