Re: [PATCH] powerpc64/bpf: support direct_call on livepatch function

[Naveen N Rao <naveen@kernel.org>]

On Mon, Dec 08, 2025 at 10:05:44PM +0530, Hari Bathini wrote:
> > 
> > One of the other thoughts I had was if we could stuff the function
> > address into the ftrace OOL stub. I had considered this back when I
> > implemented the OOL stubs, but didn't do it due to the extra memory
> > requirement. However, given the dance we're having to do, I'm now
> > thinking that may make sense and can simplify the code. If we can also
> > hook into livepatch, then we should be able to update the function
> > address in the stub to point to the new address and the trampoline
> > should then "just work" since it already saves/restores the TOC [We may
> > additionally have to update the function IP in _R12, but that would be a
> > minor change overall]
> > 
> > We will still need a way to restore livepatch TOC if the BPF trampoline
> > doesn't itself call into the function, but we may be able to handle that
> > if we change the return address to jump to a stub that restores the TOC
> > from the livepatch stack.
> 
> Sounds doable. Looking into a couple of other things at the moment
> though. Will try out this suggestion and get back post that.
> Having said that, your thoughts on whether the current approach
> is a viable option if bpf_get_func_ip() can be fixed somehow?

Oh, that's fine -- feel free to go with whatever approach you think 
works best.


- Naveen