Re: [Qemu-devel] [PATCH] display: cirrus: check vga bits per pixel(bpp) value

[Gerd Hoffmann]

On Mi, 2017-01-11 at 16:59 +0200, Alberto Garcia wrote:
> On Mon, Nov 28, 2016 at 11:52:08AM +0530, P J P wrote:
> > | > --- a/hw/display/cirrus_vga.c
> > | > +++ b/hw/display/cirrus_vga.c
> > | > @@ -272,6 +272,9 @@ static void 
> > cirrus_update_memory_access(CirrusVGAState
> > | > *s);
> > | >  static bool blit_region_is_unsafe(struct CirrusVGAState *s,
> > | >                                    int32_t pitch, int32_t addr)
> > | >  {
> > | > +    if (!pitch) {
> > | > +        return true;
> > | > +    }
> > | >
> > | 
> > | That doesn't look directly related to 'cirrus_get_bpp', care to explain?
> > 
> >   'blit_region_is_unsafe' is called from 'blit_is_unsafe' to check if blit 
> > parameters (cirrus_blt_srcpitch/cirrus_blt_dstpitch)  are safe for 
> > 'cirrus_do_copy'. These too could lead to div by zero in cirrus_do_copy
> 
> This change is causing display artifacts in QEMU 2.8.
> 
> What seems to happen is that blit_is_unsafe() is also called for
> CIRRUS_BLTMODE_PATTERNCOPY, but in this case cirrus_blt_srcpitch is
> not used. However, because of this new check if its value is 0 then
> cirrus_bitblt_common_patterncopy() returns early and becomes a no-op.

inflight vga queue pull request has a fix for that.

cheers,
  Gerd