On 9 November 2015 at 20:17, Michael S. Tsirkin <m...@redhat.com> wrote: > On Mon, Nov 09, 2015 at 02:56:31PM +0000, Peter Maydell wrote: >> Signed integer overflow in C is undefined behaviour, and the compiler >> is at liberty to assume it can never happen and optimize accordingly. >> In particular, the subtractions in hpet_time_after() and hpet_time_after64() >> were causing OSX clang to optimize the code such that it was prone to >> hangs and complaints about the main loop stalling (presumably because >> we were spending all our time trying to service very high frequency >> HPET timer callbacks). The clang sanitizer confirms the UB: >> >> hw/timer/hpet.c:119:26: runtime error: signed integer overflow: -2146967296 >> - 2147003978 cannot be represented in type 'int' >> >> Fix this by doing the subtraction as an unsigned operation and then >> converting to signed for the comparison. >> >> Reported-by: Aaron Elkins <threc...@yahoo.com> >> Signed-off-by: Peter Maydell <peter.mayd...@linaro.org> > > Agree, this makes no sense the way it's written. > > Reviewed-by: Michael S. Tsirkin <m...@redhat.com> > > I'll pick this up in the next pull if Paolo doesn't > beat me to it.
I went ahead and committed it to master yesterday; sorry if that was a bit hasty of me. thanks -- PMM
