On Thu, Dec 04, 2025 at 02:38:27PM +0000, Krzysztof Karas wrote: > vpos (int) field multiplied by crtc_htotal (u16) may cause > implicit promotion of the latter and overflow the result causing > undefined behavior.
How is that undefined? > > Cast the u16 operand to (s32) type to avoid that. > > Signed-off-by: Krzysztof Karas <[email protected]> > --- > > v4: > * use s32 cast instead of int; > > drivers/gpu/drm/drm_vblank.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c > index 32d013c5c8fc..e25dcaa6cad4 100644 > --- a/drivers/gpu/drm/drm_vblank.c > +++ b/drivers/gpu/drm/drm_vblank.c > @@ -791,7 +791,7 @@ drm_crtc_vblank_helper_get_vblank_timestamp_internal( > * since start of scanout at first display scanline. delta_ns > * can be negative if start of scanout hasn't happened yet. > */ > - delta_ns = div_s64(1000000LL * (vpos * mode->crtc_htotal + hpos), > + delta_ns = div_s64(1000000LL * (vpos * (s32)mode->crtc_htotal + hpos), > mode->crtc_clock); > > /* Subtract time delta from raw timestamp to get final > -- > 2.34.1 -- Ville Syrjälä Intel
