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

[Alberto Garcia]

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.

Berto