Re: [PATCH v6] arm64: implement ftrace with regs

[Balbir Singh]

On Fri, Jan 04, 2019 at 05:50:18PM +0000, Mark Rutland wrote:
> Hi Torsten,
> 
> On Fri, Jan 04, 2019 at 03:10:53PM +0100, Torsten Duwe wrote:
> > Use -fpatchable-function-entry (gcc8) to add 2 NOPs at the beginning
> > of each function. Replace the first NOP thus generated with a quick LR
> > saver (move it to scratch reg x9), so the 2nd replacement insn, the call
> > to ftrace, does not clobber the value. Ftrace will then generate the
> > standard stack frames.
> >

Do we know what the overhead would be, if this was a link time change
for the first instruction?

Also, I was under the impression that some arch's do ftrace_call_replace
under stop_machine(), is that a possibility here?

Balbir Singh