On 01/24/17 12:17, Laszlo Ersek wrote: > On 01/24/17 11:48, Gerd Hoffmann wrote: >>>> diff --git a/hw/display/cirrus_vga.c b/hw/display/cirrus_vga.c >>>> index 379910d..7ddd289 100644 >>>> --- a/hw/display/cirrus_vga.c >>>> +++ b/hw/display/cirrus_vga.c >>>> @@ -277,7 +277,8 @@ static bool blit_region_is_unsafe(struct >>>> CirrusVGAState *s, >>>> } >>>> if (pitch < 0) { >>>> int64_t min = addr >>>> - + ((int64_t)s->cirrus_blt_height-1) * pitch; >>>> + + ((int64_t)s->cirrus_blt_height-1) * pitch >>>> + - s->cirrus_blt_width; >>>> int32_t max = addr >>>> + s->cirrus_blt_width; >>>> if (min < 0 || max > s->vga.vram_size) { >>>> >>> >>> I believe this is incorrect. In this case (AFAIR), "addr" points to the >>> left-most pixel (= lowest address) of the bottom line (= highest >>> address). >> >> If I read the code correctly it is backwards *both* x and y axis, so >> addr is the right-most pixel of the bottom line. > > What is "max" then? If "addr" is the right-most pixel of the bottom > line, then "max" has the highest address just past the rectangle, and > then adding anything non-negative to it makes no sense.
sorry, over-editing caused a bug. I meant If "addr" is the right-most pixel of the bottom line (or just one past that), then *it* has the highest address, and then adding anything non-negative to it (i.e., how we end up with "max") makes no sense. I should have started with the diagram, not with the text. Thanks Laszlo > > Adding a negative value to it (i.e., if s->cirrus_blt_width were > negative) might make sense, for getting the leftmost pixel on the bottom > line, but then that "max" value shouldn't be used for the final boundary > check (against RAM size). > > ... Really as I remember it from the downstream review, the pitch is > negative (bottom-up), but the horizontal direction remains left to right. > > 0-----------------------------------------------------------------> x > | > | addr + (height - 1) * pitch, pitch < 0, height > 0 > | | > | v > | *--------------------* <-- addr + (height - 1) * pitch + width > | | | > | | | > | | | > | | | > | | | > | | | > | *--------------------* > | ^ ^ > | | | > | addr max = addr + width, width > 0 > | > v > y > > > The rightmost column represented here is exclusive, the rest is inclusive. > > Thanks > Laszlo >