Re: [PATCH 1/3] qemu/compiler: Simplify as all compilers support attribute 'gnu_printf'

[Daniel P . Berrangé]

On Mon, Sep 28, 2020 at 03:32:45PM +0100, Peter Maydell wrote:
> On Mon, 28 Sep 2020 at 15:23, Daniel P. Berrangé <berrange@redhat.com> wrote:
> >
> > On Mon, Sep 28, 2020 at 03:14:45PM +0100, Peter Maydell wrote:
> > > On Mon, 28 Sep 2020 at 15:06, Daniel P. Berrangé <berrange@redhat.com> 
> > > wrote:
> > > > I think this can be simplified even more by using GLib's macros
> > > >
> > > >   #define GCC_FMT_ATTR(n, m)  G_GNUC_PRINTF(n, m)
> > >
> > > At least on my system G_GNUC_PRINTF() expands to
> > > __format__(__printf__,...), not gnu_printf, so it is
> > > not quite what we want. (The difference is that on Windows
> > > hosts we still want to mark up our our logging functions as
> > > taking the glibc style format handling, not whatever the
> > > MS C library format escapes happen to be.)
> > > At a minimum you'd need to keep in the "on Windows,
> > > redefine __printf__ to __gnu_printf__" logic.
> > >
> > > See also commit 95df51a4a02a853.
> >
> > Oh, that's a bug in old GLib versions. I thought we had a new enough
> > min to avoid that problem, but i guess not after all.
> 
> Looks like the implementation changed 2 years ago:
> https://gitlab.gnome.org/GNOME/glib/-/commit/98a0ab929d8c59ee27e5f470f11d077bb6a56749
> not sure which glib version that would correspond to.

Looks like 2.58.0, which is still a fair bit newer than our 2.48 min.

NB, only the macro changed - they were using GNU printf impl for many
many years before that but simply had the wrong macro definition

We can just sacrifice -Wformat checking for Windows builds when using
old GLib. People building natively on Windows with MSys probably have
brand new GLib, and those using Fedora mingw / Debian MXE also have
pretty new GLib.

Regards,
Daniel
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