On Mon, Apr 18, 2016 at 08:39:00PM +0100, Emil Velikov wrote: > On 18 April 2016 at 16:53, Daniel Vetter <daniel@xxxxxxxx> wrote: > > On Mon, Apr 18, 2016 at 03:40:11PM +0100, Emil Velikov wrote: > >> On 18 April 2016 at 13:36, Daniel Vetter <daniel@xxxxxxxx> wrote: > >> > On Mon, Apr 18, 2016 at 12:09:51PM +0100, Lionel Landwerlin wrote: > >> >> Ping? > >> >> > >> >> On 22/03/16 14:10, Lionel Landwerlin wrote: > >> >> >When extracting the value at full precision (16 bits), no need to > >> >> >round the value. > >> >> > > >> >> >This was spotted by Jani when running sparse. Unfortunately this fix > >> >> >doesn't get rid of the warning. > >> > > >> > It sounded like no bug, and the patch itself fails to appease sparse. And > >> > I didn't check what's upsetting sparse itself, so figured "nothing to do > >> > here until a real fix shows up". > >> > > >> According to the C99 standard a left shift with negative value is > >> undefined. And we're hitting this case at full precision ;-) > > > > Well commit message says sparse is still unhappy. So I'm not sure whether > > the fix is good enough? And the issue with compiler/static checker noise > > is that we really should aim to shut them up completely, because broken > > windows and all that (even if it's sometimes a fallacy, I think it applies > > here). > Afaics the fix resolves a real bug and the final solution is bug free > (although one can drop the L form 1UL). If I have to guess I'd say > that sparse does not realise that the precision cannot be greater than > 16. > > Quick and easy check is to add an early bail out (if bit_precision > > 16 return user_input). The compiler will optimise it out anyway (it > does propagate/fold the constants) the end binary will be fine. > Another approach is the earlier suggested, switch which will also get > optimised in the final binary. Ok, count me convinced ;-) Applied to drm-misc. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
