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

Steven Rostedt
2022-03-21T16:23:16Z

On Mon, 21 Mar 2022 12:15:49 -0400
Steven Rostedt <rostedt@goodmis.org> 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