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

[Chad Joan]

Sure.

I'll see your -O2 and raise you a -c ;)

It went like this:

$ gcc -c first.c -O2
$ gcc -c second.c -O2
$ gcc -c third.c -O2

No complaints from gcc whatsoever (unless I drop the -c, then ld complains about the undefined reference to main, which I think we all expect).

Just incase you expected one of them to fail (ex: as a control test), I verified that the original snippet from the configure script still causes an error on the system:
#########
$ cat << EOF > reference.c
> #include <locale.h>
> #include <curses.h>
> #include <wchar.h>
> int main(void) {
>   const char *s = curses_version();
>   wchar_t wch = L'w';
>   setlocale(LC_ALL, "");
>   resize_term(0, 0);
>   addwstr(L"wide chars\n");
>   addnwstr(&wch, 1);
>   add_wch(WACS_DEGREE);
>   return s != 0;
> }
> EOF
$ gcc reference.c -O2
reference.c: In function 'main':
reference.c:11:11: error: 'WACS_DEGREE' undeclared (first use in this function)
   add_wch(WACS_DEGREE);
           ^
reference.c:11:11: note: each undeclared identifier is reported only once for each function it appears in

#########

Hope that helps.

On Fri, Feb 17, 2017 at 6:11 AM, Paolo Bonzini <address@hidden> wrote:

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