On Fri, Jan 11, 2019 at 1:22 PM Josh Poimboeuf <jpoim...@redhat.com> wrote: > > On Fri, Jan 11, 2019 at 12:46:39PM -0800, Linus Torvalds wrote: > > On Fri, Jan 11, 2019 at 12:31 PM Josh Poimboeuf <jpoim...@redhat.com> wrote: > > > > > > I was referring to the fact that a single static call key update will > > > usually result in patching multiple call sites. But you're right, it's > > > only 1-2 trampolines per text_poke_bp() invocation. Though eventually > > > we may want to batch all the writes like what Daniel has proposed for > > > jump labels, to reduce IPIs. > > > > Yeah, my suggestion doesn't allow for batching, since it would > > basically generate one trampoline for every rewritten instruction. > > As Andy said, I think batching would still be possible, it's just that > we'd have to create multiple trampolines at a time. > > Or... we could do a hybrid approach: create a single custom trampoline > which has the call destination patched in, but put the return address in > %rax -- which is always clobbered, even for callee-saved PV ops. Like: >
One think I particularly like about the current design is that there are no requirements at all on the calling convention. I think it seems fragile to add a calling convention constraint that only applies when there's a race. I'd rather do a longjmp-like hack or a stack gap adding hack than make the actual static calls more fragile.
