On Tue, May 08, 2018 at 05:17:40PM +0200, Paolo Bonzini wrote:
> On 04/05/2018 18:00, Daniel P. Berrangé wrote:
> > There are two useful macros that can be defined before including
> > glib.h that are related to the min required glib version
> >
> > - GLIB_VERSION_MIN_REQUIRED
> >
> > When this is defined, if code uses an API that was deprecated
> > in this version, or older, a compiler warning will be emitted.
> > This alerts maintainers to update their code to whatever new
> > replacement API is now recommended best practice.
> >
> > - GLIB_VERSION_MAX_ALLOWED
> >
> > When this is defined, if code uses an API that was introduced
> > in a version that is newer than the declared version, a compiler
> > warning will be emitted. This alerts maintainers if new code
> > accidentally uses functionality that won't be available on some
> > supported platforms.
> >
> > The GLIB_VERSION_MAX_ALLOWED constant makes it a bit harder to opt
> > in to using specific new APIs with a GLIB_CHECK_VERSION conditional.
> > To workaround this Pragmas can be used to temporarily turn off the
> > -Wdeprecated-declarations compiler warning, while a static inline
> > compat function is implemented. Nothing needs that at this time,
> > so just illustrate it in a comment for benefit of future changes.
>
> Unfortunately there is one need, and it's a bug in glib itself:
>
> In file included from /usr/lib64/glib-2.0/include/glibconfig.h:9:0,
> from /usr/include/glib-2.0/glib/gtypes.h:32,
> from /usr/include/glib-2.0/glib/galloca.h:32,
> from /usr/include/glib-2.0/glib.h:30,
> from
> /home/pbonzini/work/upstream/qemu/include/glib-compat.h:29,
> from
> /home/pbonzini/work/upstream/qemu/include/qemu/osdep.h:107,
> from /home/pbonzini/work/upstream/qemu/disas/arm-a64.cc:21:
> /usr/include/glib-2.0/glib/glib-autocleanups.h: In function ‘void
> glib_autoptr_cleanup_GOptionGroup(GOptionGroup**)’:
> /usr/include/glib-2.0/glib/glib-autocleanups.h:63:45: error: ‘void
> g_option_group_unref(GOptionGroup*)’ is deprecated (declared at
> /usr/include/glib-2.0/glib/goption.h:372): Not available before 2.44
> [-Werror=deprecated-declarations]
> G_DEFINE_AUTOPTR_CLEANUP_FUNC(GOptionGroup, g_option_group_unref)
> ^
> /usr/include/glib-2.0/glib/gmacros.h:444:88: note: in definition of macro
> ‘G_DEFINE_AUTOPTR_CLEANUP_FUNC’
> static inline void _GLIB_AUTOPTR_FUNC_NAME(TypeName) (TypeName **_ptr) {
> if (*_ptr) (func) (*_ptr); } \
>
> ^
> /usr/include/glib-2.0/glib/gmacros.h:444:100: error: ‘void
> g_option_group_unref(GOptionGroup*)’ is deprecated (declared at
> /usr/include/glib-2.0/glib/goption.h:372): Not available before 2.44
> [-Werror=deprecated-declarations]
> static inline void _GLIB_AUTOPTR_FUNC_NAME(TypeName) (TypeName **_ptr) {
> if (*_ptr) (func) (*_ptr); } \
>
> ^
> /usr/include/glib-2.0/glib/glib-autocleanups.h:63:1: note: in expansion of
> macro ‘G_DEFINE_AUTOPTR_CLEANUP_FUNC’
> G_DEFINE_AUTOPTR_CLEANUP_FUNC(GOptionGroup, g_option_group_unref)
>
> (This is RHEL7 glib2-2.50.3-3.el7.x86_64).
>
> Luckily you suggested the solution yourself---this seems to work:
>
> diff --git a/include/glib-compat.h b/include/glib-compat.h
> index d066f6d..ef07489 100644
> --- a/include/glib-compat.h
> +++ b/include/glib-compat.h
> @@ -26,6 +26,8 @@
> */
> #define GLIB_VERSION_MAX_ALLOWED GLIB_VERSION_2_42
>
> +_Pragma("GCC diagnostic push")
> +_Pragma("GCC diagnostic ignored \"-Wdeprecated-declarations\"")
> #include <glib.h>
>
> /*
> @@ -42,8 +44,6 @@
> * signature that does what we need, but with a "_qemu"
> * suffix eg
> *
> - * _Pragma("GCC diagnostic push")
> - * _Pragma("GCC diagnostic ignored \"-Wdeprecated-declarations\"")
> * static inline void g_foo_qemu(const char *wibble)
> * {
> * #if GLIB_CHECK_VERSION(X, Y, 0)
> @@ -52,12 +52,10 @@
> * g_something_equivalent_in_older_glib(wibble);
> * #endif
> * }
> - * _Pragma("GCC diagnostic pop")
> *
> - * The Pragma calls turn off -Wdeprecated-declarations,
> - * ensuring this wrapper function impl doesn't trigger the
> - * compiler warning about using too new glib APIs. Finally
> - * we can do
> + * The _Pragma at the top of this file turns off -Wdeprecated-declarations,
> + * ensuring this wrapper function impl doesn't trigger the compiler warning
> + * about using too new glib APIs. Finally we can do
> *
> * #define g_foo(a) g_foo_qemu(a)
> *
> @@ -94,4 +92,6 @@ gint g_poll_fixed(GPollFD *fds, guint nfds, gint timeout);
> } while (0)
> #endif
>
> +_Pragma("GCC diagnostic pop")
> +
> #endif
>
> I'll give it a shot on clang too.
Ok, that change looks fine with me assuming it passes your build tests.
In fact that is what I had done in an earlier version.
Regards,
Daniel
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