Re: [PATCH] powerpc/ftrace: restore r2 to caller's stack on livepatch sibling call

["Ryan B. Sullivan" <rysulliv@redhat.com>]

On Tue, Sep 10, 2024 at 05:21:57PM +1000, Michael Ellerman wrote:
> "Ryan B. Sullivan" <rysulliv@redhat.com> writes:
> > Hello all,
> >
> > Just wanted to ping and see if there was any further feedback or
> > questions regarding the patch?
> 

Hi Michael,

Thank you for the update.

> Hi Ryan,
> 
> I'd really like a selftest that triggers the sibling call behaviour.
> 
> As I said upthread I tried writing one but failed. Which you later
> explained is because the cross-module sibling call is not generated by
> the compiler but rather by the code being objcopy'ed (or similar).
> 
> I think it should be possible to trick the compiler into letting us do a
> cross-module sibling call by doing it in an inline asm block. Obviously
> that's non-standard, but I think it might work well enough for a test?
> 
> We have an example of calling a function within an inline asm block in
> call_do_irq().

If you think that that would be a welcome addition to the patch I can
look into adding it, especially if you are busy at the moment.

> 
> I'll try to find time to get that done, but I can't promise when.
> 
> cheers
> 

Cheers,

Ryan