On Mon, Mar 27, 2023 at 02:47:40PM +0200, Michal Privoznik wrote:
There are couple of g_dbus_*() functions we provide an alternative implementation for in our virgdbusmock.c. However, these functions are declared in gio/gdbusconnection.h as:
GIO_AVAILABLE_IN_ALL GDBusConnection *g_bus_get_sync (GBusType bus_type, GCancellable *cancellable, GError **error);
where GIO_AVAILABLE_IN_ALL is declared as (in /gio/gio-visibility.h):
#if (defined(_WIN32) || defined(__CYGWIN__)) && !defined(GIO_STATIC_COMPILATION) # define _GIO_EXPORT __declspec(dllexport) # define _GIO_IMPORT __declspec(dllimport) #elif __GNUC__ >= 4 # define _GIO_EXPORT __attribute__((visibility("default"))) # define _GIO_IMPORT #else # define _GIO_EXPORT # define _GIO_IMPORT #endif #ifdef GIO_COMPILATION # define _GIO_API _GIO_EXPORT #else # define _GIO_API _GIO_IMPORT #endif
#define _GIO_EXTERN _GIO_API extern
#define GIO_AVAILABLE_IN_ALL _GIO_EXTERN
Now, on mingw the functions we mock are declared with dllimport attribute which makes the compiler unhappy:
../tests/virgdbusmock.c:25:24: error: 'g_bus_get_sync' redeclared without dllimport attribute: previous dllimport ignored [-Werror=attributes]
The solution is to do what glib does when it compiles the gio module: set GIO_COMPILATION macro which in turn annotates the function with dllexport attribute.
I will point out that GIO_COMPILATION is not intended to be used outside of GLib: it signals that the gio module is in the process of being built, which can result (as is the case here) in different behavior compared to what you'd see when building *against* gio. So defining it as part of building libvirt is quite yucky, and I wouldn't be surprised if this trick stopped working or ended up causing other unintended consequences in the future. Unfortunately, I also don't really have a better alternative to suggest, so I guess it is what it is :) -- Andrea Bolognani / Red Hat / Virtualization