[Spice-devel] [PATCH] Avoid passing libusb functions as callbacks

[Jorge Olmos]

Hi,
On Fri, 2018-08-17 at 15:24 +0200, Victor Toso wrote:
> Hi,
> 
> On Fri, Aug 17, 2018 at 03:12:35PM +0200, jorge.olmos at flexvdi.com
> wrote:
> > From: Jorge Olmos <jorge.olmos at flexvdi.com>
> > 
> > When building spice-gtk for windows:
> > - libusb uses __stdcall calling convention when compiled for win32.
> > It does
> > not include an option to be compiled with __cdecl calling
> > convention.
> > Directly calling libusb functions works fine. But it is a problem
> > when its
> > functions are passed as callbacks to a function that expects other
> > calling
> > convention.
> > - glib uses __cdecl calling convention and expects the functions it
> > receives as parameters to follow __cdecl convention.
> > 
> > So the lines included in spice-gtk like:
> >      g_clear_pointer(&priv->device, libusb_unref_device);
> > cause libusb_unref_device (compiled with _stdcall convention) to be
> > called
> > with __cdecl convention. This causes stack corruption, and hence
> > crashes.
> 
> Have you raised a bug in glib? We use this libraries to help with
> portability so I'd hope it is possible to fix in glib.
> 

I don't think it is even possible to fix this cleanly in glib. A
compilation of glib can work well with __stdcall OR with __cdecl. But
not with both of them.

Right now I have just found another patch in spice-gtk, where the same
problem was solved with the same solution, which also has no
portability issues:

https://patchwork.freedesktop.org/patch/92705/



> > ---
> >  src/channel-usbredir.c | 9 ++++++---
> >  1 file changed, 6 insertions(+), 3 deletions(-)
> > 
> > diff --git a/src/channel-usbredir.c b/src/channel-usbredir.c
> > index 6ffe546..1d9c380 100644
> > --- a/src/channel-usbredir.c
> > +++ b/src/channel-usbredir.c
> > @@ -352,7 +352,8 @@ static void spice_usbredir_channel_open_acl_cb(
> >          spice_usbredir_channel_open_device(channel, &err);
> >      }
> >      if (err) {
> > -        g_clear_pointer(&priv->device, libusb_unref_device);
> > +        libusb_unref_device(priv->device);
> > +        priv->device = NULL;
> >          g_boxed_free(spice_usb_device_get_type(), priv-
> > >spice_device);
> >          priv->spice_device = NULL;
> >          priv->state  = STATE_DISCONNECTED;
> > @@ -383,7 +384,8 @@ _open_device_async_cb(GTask *task,
> >      spice_usbredir_channel_lock(channel);
> >  
> >      if (!spice_usbredir_channel_open_device(channel, &err)) {
> > -        g_clear_pointer(&priv->device, libusb_unref_device);
> > +        libusb_unref_device(priv->device);
> > +        priv->device = NULL;
> >          g_boxed_free(spice_usb_device_get_type(), priv-
> > >spice_device);
> >          priv->spice_device = NULL;
> >      }
> > @@ -504,7 +506,8 @@ void
> > spice_usbredir_channel_disconnect_device(SpiceUsbredirChannel
> > *channel)
> >  
> >          /* This also closes the libusb handle we passed from
> > open_device */
> >          usbredirhost_set_device(priv->host, NULL);
> > -        g_clear_pointer(&priv->device, libusb_unref_device);
> > +        libusb_unref_device(priv->device);
> > +        priv->device = NULL;
> >          g_boxed_free(spice_usb_device_get_type(), priv-
> > >spice_device);
> >          priv->spice_device = NULL;
> >          priv->state  = STATE_DISCONNECTED;
> > -- 
> > 2.14.4
> > 
> > _______________________________________________
> > Spice-devel mailing list
> > Spice-devel at lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/spice-devel
> 
> 
-- 


Jorge Olmos
Software Engineer
jorge.olmos at flexvdi.com
+34 876 60 00 73
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