On Wed, Feb 02, 2022 at 04:48:52PM +0000, Sean Christopherson wrote: > > > +"movb " __stringify(KVM_STEAL_TIME_preempted) "+steal_time(%rax), %al;" > > > +"andl $" __stringify(KVM_VCPU_PREEMPTED) ", %eax;" > > > +"setnz %al;" > > > > Isn't the below the simpler way of writing that same? > > The AND is needed to clear RAX[63:8], e.g. to avoid breakage if the return value > is changed from a bool to something larger, or the compiler uses more than a byte > for _Bool. While C doesn't specify _Bool the arch ABI most certainly does, and x86_64 ABI guarantees a byte there, changing the return type is the only possible option here. Anyway, I don't mind the patch and the proposed Changelog does clarify that this is an exercise in paranoia.
