On Fri, Feb 04, 2022 at 09:35:49AM -0800, Sami Tolvanen wrote: > On Wed, Feb 2, 2022 at 10:43 AM Sean Christopherson <seanjc@xxxxxxxxxx> wrote: > > > +DEFINE_STATIC_CALL_RET0(__perf_guest_state, *perf_guest_cbs->state); > > > +DEFINE_STATIC_CALL_RET0(__perf_guest_get_ip, *perf_guest_cbs->get_ip); > > > +DEFINE_STATIC_CALL_RET0(__perf_guest_handle_intel_pt_intr, *perf_guest_cbs->handle_intel_pt_intr); > > > > Using __static_call_return0() makes clang's CFI sad on arm64 due to the resulting > > function prototype mistmatch, which IIUC, is verified by clang's __cfi_check() > > for indirect calls, i.e. architectures without CONFIG_HAVE_STATIC_CALL. > > > > We could fudge around the issue by using stubs, massaging prototypes, etc..., but > > that means doing that for every arch-agnostic user of __static_call_return0(). > > > > Any clever ideas? Can we do something like generate a unique function for every > > DEFINE_STATIC_CALL_RET0 for CONFIG_HAVE_STATIC_CALL=n, e.g. using typeof() to > > get the prototype? > > I'm not sure there's a clever fix for this. On architectures without > HAVE_STATIC_CALL, this is an indirect call to a function with a > mismatching type, which CFI is intended to catch. > > The obvious way to solve the problem would be to use a stub function > with the correct type, which I agree, isn't going to scale. You can > alternatively check if .func points to __static_call_return0 and not > make the indirect call if it does. If neither of these options are > feasible, you can disable CFI checking in the functions that have > these static calls using the __nocfi attribute. There's also the tp_stub_func() thing that does basically the same thing.
