Re: [PATCH v4 1/3] arm64: implement ftrace with regs

[Mark Rutland]

On Wed, Oct 31, 2018 at 02:19:07PM +0100, Jiri Kosina wrote:
> On Wed, 31 Oct 2018, Mark Rutland wrote:
> 
> > I guess skipping the original function prologue would simplify the
> > implementation of the replacement function (and would mean that the regs
> > held the function arguments per the procedure call standard), but AFAICT
> > other architectures aren't relying on that, so it doesn't seem to be a
> > strict requirement.
> > 
> > What am I missing?
> > 
> > How does livepatching handle the pre-mcount function preambles on
> > architectures with existing support?
> 
> Other architectures do rely on that. That's exactly for example why on x86 
> we use '-pg -mfentry', to make sure we hook the function *before* 
> prologue.

Ah, I'd missed -mfentry for x86. I now see that's also the case with
__gnu_mcount_nc on arch/arm, so that covers my confusion.

Thanks for correcting me, and sorry for noise!

Mark.