On Fri, Aug 10, 2018 at 11:27:37AM -0700, Palmer Dabbelt wrote: > On Fri, 10 Aug 2018 01:38:04 PDT (-0700), Christoph Hellwig wrote: > >On Thu, Aug 09, 2018 at 03:19:51PM -0700, Palmer Dabbelt wrote: > >>This would be necessary to make non-SMP builds work, but there is > >>another error in the implementation of our syscall linkage that actually > >>just causes sys_riscv_flush_icache to never build. I've build tested > >>this on allnoconfig and allnoconfig+SMP=y, as well as defconfig like > >>normal. > > > >Would't it make sense to use COND_SYSCALL to stub out the syscall > >for !SMP builds? > > I'm not sure. We can implement the syscall fine in !SMP, it's just that the > vDSO is expected to always eat these calls because in non-SMP mode you can > do a global fence.i by just doing a local fence.i (there's only one hart). > > The original rationale behind not having the syscall in non-SMP mode was to > limit the user ABI, but on looking again that seems like it's just a bit of > extra complexity that doesn't help anything. It's already been demonstrated
Doesn't this mean that some userspace code will only run if the kernel was compiled for SMP ? I always thought that was unacceptable. Guenter > that nothing is checking the error because it's been silently slipping past > userspace for six months, so the extra complexity seems like it'll just > cause someone else to have to chase the bug in the future. > > But I'm really OK either way. Is there a precedent for what to do here?