On Tue, Sep 19, 2023 at 03:22:25PM +0000, David Laight wrote: > > Anyway, that's not the brief. We're looking to (eg) clear bit 0 > > and test whether bit 7 was set. So it's the sign bit of the byte, > > not the sign bit of the int. > > Use the address of the byte as an int and xor with 1u<<24. > The xor will do a rmw on the three bytes following, but I > doubt that matters. Bet you a shiny penny that Coldfire takes an unaligned access trap ... and besides, this is done on _every_ call to unlock_page(). That might cross not only a cacheline boundary but also a page boundary. I cannot believe that would be a high-performing solution. It might be just fine on m68000 but I bet even by the 030 it's lower performing.
