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.
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
include/glib-compat.h | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 49 insertions(+)
diff --git a/include/glib-compat.h b/include/glib-compat.h
index 3b340ab33c..d066f6d257 100644
--- a/include/glib-compat.h
+++ b/include/glib-compat.h
@@ -16,8 +16,57 @@
#ifndef QEMU_GLIB_COMPAT_H
#define QEMU_GLIB_COMPAT_H
+/* Ask for warnings for anything that was marked deprecated in
+ * the defined version, or before. It is a candidate for rewrite.
+ */
+#define GLIB_VERSION_MIN_REQUIRED GLIB_VERSION_2_42
+
+/* Ask for warnings if code tries to use function that did not
+ * exist in the defined version. These risk breaking builds
+ */
+#define GLIB_VERSION_MAX_ALLOWED GLIB_VERSION_2_42
+
#include <glib.h>
+/*
+ * Note that because of the GLIB_VERSION_MAX_ALLOWED constant
+ * above, allowing use of functions from newer GLib via this
+ * compat header needs a little trickery to prevent warnings
+ * being emitted.
+ *
+ * Consider a function from newer glib-X.Y that we want to use
+ *
+ * int g_foo(const char *wibble)
+ *
+ * We must define a static inline function with the same
+ * 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)
+ * g_foo(wibble)
+ * #else
+ * 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
+ *
+ * #define g_foo(a) g_foo_qemu(a)
+ *
+ * So now the code elsewhere in QEMU, which *does* have the
+ * -Wdeprecated-declarations warning active, can call
+ * g_foo(...) as normal, without generating warnings.
+ */
+
+
#if defined(_WIN32) && !GLIB_CHECK_VERSION(2, 50, 0)
/*
* g_poll has a problem on Windows when using
--
2.14.3
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.
Paolo
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
--
|: https://berrange.com -o- https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org -o- https://fstop138.berrange.com :|
|: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
On 08/05/2018 17:19, Daniel P. Berrangé wrote: > 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 Actually there is a use of g_strv_contains in tests/test-qga.c. It is guarded by GLIB_CHECK_VERSION(2, 44, 0) but the right fix should be to include the compatibility function instead. For now I am dropping this patch. Paolo
On Tue, May 08, 2018 at 06:02:55PM +0200, Paolo Bonzini wrote: > On 08/05/2018 17:19, Daniel P. Berrangé wrote: > > 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 > > Actually there is a use of g_strv_contains in tests/test-qga.c. It is > guarded by GLIB_CHECK_VERSION(2, 44, 0) but the right fix should be to > include the compatibility function instead. > > For now I am dropping this patch. Ok, I'll have a look at that, and re-post an updated patch later. There are a few other uses of GLIB_CHECK_VERSION to be investigated too I see. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
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