Re: [Qemu-devel] Fix build break during configuration on musl-libc based Linux systems.

["Rainer Müller" <raimue@codingfarm.de>]

On 2017-02-17 17:57, Peter Maydell wrote:
> On 17 February 2017 at 11:20, Paolo Bonzini <pbonzini@redhat.com> wrote:
>>
>>
>> On 17/02/2017 11:18, Peter Maydell wrote:
>>> Defining _XOPEN_SOURCE is easy enough, and I think we should
>>> do it unconditionally. We should check what effect this has
>>> on the BSD hosts though I guess. (You could argue that we
>>> should be defining _XOPEN_SOURCE anyway for the benefit of
>>> the non-glibc BSD/Solaris/etc platforms.)
>>
>> Sounds good, then I think we should define it to 700 just like glibc does.
> 
> Unfortunately this idea turns out to break OSX compiles,
> because on OSX saying _XOPEN_SOURCE=anything disables
> all the non-X/Open APIs (which you get by default, and
> some of which like mkdtemp we use).

A bit late to this thread, but the original problem was also reported
for Mac OS X with --enable-curses in MacPorts. The build fails with the
same symptoms as in the original report.

https://trac.macports.org/ticket/53929

As you identified, the problem is that ncurses expects the define
_XOPEN_SOURCE >= 500 to enable the wide-char function declarations.

The solution to retain access to non-standard API on Mac OS X would be
to also define _DARWIN_C_SOURCE which enables extensions.

$ cat foo.c
#include <unistd.h>
int main() {
    mkdtemp("/tmp/test-XXXXXX");
}
$ cc -D_XOPEN_SOURCE=500 -c foo.c
foo.c:4:5: warning: implicit declaration of function 'mkdtemp' is
invalid in C99 [-Wimplicit-function-declaration]
    mkdtemp("/tmp/test-XXXXXX");
    ^
1 warning generated.
$ cc -D_XOPEN_SOURCE=500 -D_DARWIN_C_SOURCE -c foo.c
$

A quick test on current master with configure patched to define
  QEMU_CFLAGS="-D_XOPEN_SOURCE=500 -D_DARWIN_C_SOURCE $QEMU_CFLAGS"
compiled fine for both a default configure and with --enable-curses.

Rainer