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

[Paolo Bonzini]

On 17/02/2017 10:17, Laszlo Ersek wrote:
> Of course, *if* that other C library, and the Curses implementation,
> claim compatibility with glibc as far as _GNU_SOURCE goes, *then* I
> fully agree with you. (IOW, it depends on the condition that you
> formulated above, "if musl wants to support _GNU_SOURCE".)

They at least try, since their features.h supports it.

> Same for ncurses -- do they aim at SUSv2 conformance, or do they intend
> to consider _GNU_SOURCE specifically?

Well, ncurses is a GNU project so I suppose they mostly care about
whatever Autoconf does.  And indeed Autoconf does have some special
casing for -D_XOPEN_SOURCE=500:

  AC_CACHE_CHECK([whether _XOPEN_SOURCE should be defined],
    [ac_cv_should_define__xopen_source],
    [ac_cv_should_define__xopen_source=no
     AC_COMPILE_IFELSE(
       [AC_LANG_PROGRAM([[
          #include <wchar.h>
          mbstate_t x;]])],
       [],
       [AC_COMPILE_IFELSE(
          [AC_LANG_PROGRAM([[
             #define _XOPEN_SOURCE 500
             #include <wchar.h>
             mbstate_t x;]])],
          [ac_cv_should_define__xopen_source=yes])])])
  test $ac_cv_should_define__xopen_source = yes &&
    AC_DEFINE([_XOPEN_SOURCE], [500])

If musl needs _XOPEN_SOURCE for wchar.h, then it would be worth working
around in QEMU.  If it's just happening with ncurses, however, it'd be a
musl bug, which should be fixed in musl or worked around in ncurses.

Chad, can you check whether the programs below fails with musl:

/* First program */
#define _GNU_SOURCE
#include <wchar.h>
mbstate_t x;

/* Second program */
#include <wchar.h>
mbstate_t x;

/* Third program */
#define _XOPEN_SOURCE 500
#include <wchar.h>
mbstate_t x;

Just compile them with "gcc foo.c -O2".

Thanks,

Paolo