----- On Nov 18, 2020, at 9:02 AM, rostedt rostedt@goodmis.org wrote:

On Wed, 18 Nov 2020 14:21:36 +0100
Peter Zijlstra [off-list ref] wrote:

quoted

I think that as long as the function is completely empty (it never
touches any of the arguments) this should work in practise.

That is:

  void tp_nop_func(void) { }

My original version (the OP of this thread) had this:

+static void tp_stub_func(void)
+{
+	return;
+}

quoted

can be used as an argument to any function pointer that has a void
return. In fact, I already do that, grep for __static_call_nop().

I'm not sure what the LLVM-CFI crud makes of it, but that's their
problem.

If it is already done elsewhere in the kernel, then I will call this
precedence, and keep the original version.

It works for me. Bonus points if you can document in a comment that this
trick depends on the cdecl calling convention.

Thanks,

Mathieu

This way Alexei can't complain about adding a check in the fast path of
more than one callback attached.

-- Steve

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com