Subject: Re: linux-next: build warnings after merge of the tip tree

From: Steven Rostedt <[email-masked]>
Date: Mon, 21 Mar 2022 12:22:59 -0400

On Mon, 21 Mar 2022 12:15:49 -0400
Steven Rostedt <[email-masked]> wrote:

> And I just thought of another issue, where even my solution wont fix it.
> What happens if we trace funcA but not funcB? How do we get to trace the
> end of funcA?

The only solution I can think of to handle all these cases is if you enable
-mfexit, you have to disable tail calls completely. That's going to cause
a performance impact.

Perhaps we need need compiler help to give us a way to hijack the return
address. But is there a way to do this and still not give up the security
that CET SHSTK gives us?

Or maybe another solution is:

funcA:
	[..]
	jmp funcB
	call __fexit__
	ret

And if funcA is being traced, we change jmp to a call.

	[..]
	call funcB
	call __fexit__
	ret

Such that we only remove the tail calls if we enable tracing on the
function with the tail call.

-- Steve