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

Peter Zijlstra
2022-03-21T16:05:13Z

On Mon, Mar 21, 2022 at 11:28:05AM -0400, Steven Rostedt wrote:
> On Mon, 21 Mar 2022 14:04:05 +0100
> Peter Zijlstra <peterz@infradead.org> wrote:

> > Also, folks, I'm thinking we should start to move to __fexit__, if CET
> > SHSTK ever wants to come to kernel land return trampolines will
> > insta-stop working.
> >
> > Hjl, do you think we could get -mfexit to go along with -mfentry ?

> int funcA () {
> [..]
> return funcB();
> }

> This currently works with function graph and kretprobe tracing because of
> the shadow stack. Let's say we traced both funcA and funcB
>
> funcA:
> call __fentry__
push funcA on trace-stack
>
> [..]
> jmp funcB
>
> funcB:
> call __fentry__
push funcB on trace-stack
>
> [..]
call __fexit__
pop trace-stack until empty
'exit funcB'
'exit funcA'

> ret

>
> That is, the current algorithm traces the end of both funcA and funcB
> without issue, because of how the shadow stack works.

And it all works, no? Or what am I missing?