On Thu, 2007-11-01 at 10:41 -0700, Jeremy Fitzhardinge wrote: > Keir Fraser wrote: > > volatile prevents the asm from being 'moved significantly', according to the > > gcc manual. I take that to mean that reordering is not allowed. > > I understood it as reordering was permitted, but no re-ordering across another volatile load, store, or asm was permitted. And of course, as long as input and output constraints are written properly, the re-ordering should not be vulnerable to pathological movement causing the code to malfunction. It seems that CPU state side effects which can't be expressed in C need special care - FPU is certainly one example. Also, memory clobber on a volatile asm should stop invalid movement across TLB flushes and other problems areas. Even memory fences should have memory clobber in order to stop movement of loads and stores across the fence by the compiler. Zach _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/virtualization
