Re: [PATCH] tracepoint: Fix CFI failures with tp_stub_func

[Mathieu Desnoyers]

On 2023-03-23 14:42, Steven Rostedt wrote:
> On Thu, 23 Mar 2023 14:37:15 -0400
> Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> wrote:
>
> > > Repeated again so Mathieu doesn't have to search for it.
> > >
> > >       [ Note, this version does use undefined compiler behavior (assuming that
> > >         a stub function with no parameters or return, can be called by a location
> > >         that thinks it has parameters but still no return value. Static calls
> > >         do the same thing, so this trick is not without precedent.
> > >
> > >         There's another solution that uses RCU tricks and is more complex, but
> > >         can be an alternative if this solution becomes an issue.
> > >
> > >         Link: https://lore.kernel.org/lkml/20210127170721.58bce7cc@xxxxxxxxxxxxxxxxxx/
> > >       ]
> >
> > Ugh. The last thing we need there is more RCU complexity. My brain is still recovering
> > from fixing the last time the introduction of static calls special-cases ended up subtly
> > breaking tracepoints.
>
> Well, we can go back to your approach with doing the check in the iterator.
> Setting it to 0x1UL I think is what you wanted (to know it's a removed
> function and not a random NULL).
>
> I could write that up if you want.

I can write the patch and send an RFC, won't take long.

Thanks,

Mathieu

> -- Steve

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