Re: Another SIGFPE in display code, now in cirrus

On Thu, 13 May 2010, Avi Kivity wrote:
> >       /* extra x, y */
> > -    sx = (src % ABS(s->cirrus_blt_srcpitch)) / depth;
> > -    sy = (src / ABS(s->cirrus_blt_srcpitch));
> > +    sx = (src % line_offset) / depth;
> > +    sy = (src / line_offset);
> >    
> 
> Does anything prevent the guest from programming the CRTC display pitch 
> to 0?
> 

Nope, I'll use line_offset there too to prevent possible divisions by 0.


> >       dx = (dst % ABS(s->cirrus_blt_dstpitch)) / depth;
> >       dy = (dst / ABS(s->cirrus_blt_dstpitch));
> >
> > @@ -725,18 +727,23 @@ static void cirrus_do_copy(CirrusVGAState *s, int dst, int src, int w, int h)
> >   		      s->cirrus_blt_dstpitch, s->cirrus_blt_srcpitch,
> >   		      s->cirrus_blt_width, s->cirrus_blt_height);
> >
> > -    if (notify)
> > -	qemu_console_copy(s->vga.ds,
> > -			  sx, sy, dx, dy,
> > -			  s->cirrus_blt_width / depth,
> > -			  s->cirrus_blt_height);
> > -
> > -    /* we don't have to notify the display that this portion has
> > -       changed since qemu_console_copy implies this */
> > -
> > -    cirrus_invalidate_region(s, s->cirrus_blt_dstaddr,
> > -				s->cirrus_blt_dstpitch, s->cirrus_blt_width,
> > -				s->cirrus_blt_height);
> > +     if (ABS(s->cirrus_blt_dstpitch) != line_offset ||
> > +             ABS(s->cirrus_blt_srcpitch) != line_offset) {
> > +             /* this is not going to happen very often */
> > +             vga_hw_invalidate();
> >    
> 
> I think we need to consider only dstpitch for a full invalidate.  We 
> might be copying an offscreen bitmap into the screen, and srcpitch is 
> likely to be the bitmap width instead of the screen pitch.
> 

Agreed.

> 
> > +     } else {
> > +         if (notify)
> > +             /* we don't have to notify the display that this portion has
> > +                changed since qemu_console_copy implies this */
> > +             qemu_console_copy(s->vga.ds,
> > +                               sx, sy, dx, dy,
> > +                               s->cirrus_blt_width / depth,
> > +                               s->cirrus_blt_height);
> > +         else
> > +             cirrus_invalidate_region(s, s->cirrus_blt_dstaddr,
> > +                                      s->cirrus_blt_dstpitch, s->cirrus_blt_width,
> > +                                      s->cirrus_blt_height);
> > +     }
> >   }
> >
> >   static int cirrus_bitblt_videotovideo_copy(CirrusVGAState * s)
> > diff --git a/hw/cirrus_vga_rop.h b/hw/cirrus_vga_rop.h
> > index 39a7b72..80f135b 100644
> > --- a/hw/cirrus_vga_rop.h
> > +++ b/hw/cirrus_vga_rop.h
> > @@ -32,10 +32,10 @@ glue(cirrus_bitblt_rop_fwd_, ROP_NAME)(CirrusVGAState *s,
> >       dstpitch -= bltwidth;
> >       srcpitch -= bltwidth;
> >
> > -    if (dstpitch<  0 || srcpitch<  0) {
> > -        /* is 0 valid? srcpitch == 0 could be useful */
> > +    if (dstpitch<  0)
> >           return;
> > -    }
> > +    if (srcpitch<  0)
> > +        srcpitch = 0;
> >    
> 
> Why?

I wouldn't want an operation that is supposed to be a forward copy
to become a backward copy instead.
With the way the code is currently written in cirrus_vga it shouldn't be
possible, but it might be a good idea to have the checks anyway.
Actually the limit I wrote is too strict, I'll fix it.
 

---

Stefano Stabellini wrote:
[]
> diff --git a/hw/cirrus_vga.c b/hw/cirrus_vga.c
> index 9f61a01..81c443b 100644
> --- a/hw/cirrus_vga.c
> +++ b/hw/cirrus_vga.c

The same as with previous patch: Yellow screen
(instead of crashing), and two lines on the
stderr:

BUG: kvm_dirty_pages_log_enable_slot: invalid parameters
BUG: kvm_dirty_pages_log_enable_slot: invalid parameters

Thanks!

/mjt

Stefano Stabellini wrote:
> > I think we need to consider only dstpitch for a full invalidate.  We 
> > might be copying an offscreen bitmap into the screen, and srcpitch is 
> > likely to be the bitmap width instead of the screen pitch.
> 
> Agreed.

Even when copying on-screen (or partially on-screen), the srcpitch
does not affect the invalidated area.  The source area might be
strange (parallelogram, single line repeated), but srcpitch should
only affect whether qemu_console_copy can be used, not the
invalidation.

-- Jamie

On Thu, 13 May 2010, Michael Tokarev wrote:
> Stefano Stabellini wrote:
> []
> > diff --git a/hw/cirrus_vga.c b/hw/cirrus_vga.c
> > index 9f61a01..81c443b 100644
> > --- a/hw/cirrus_vga.c
> > +++ b/hw/cirrus_vga.c
> 
> The same as with previous patch: Yellow screen
> (instead of crashing), and two lines on the
> stderr:
> 
> BUG: kvm_dirty_pages_log_enable_slot: invalid parameters
> BUG: kvm_dirty_pages_log_enable_slot: invalid parameters
> 

I tried to do the same thing on WinNT with qemu (thanks to
Michael for providing me the image) and it works OK with the
patch applied.

I think there must be another bug in the kvm dirty page handling...