Re: [RFC perf/core 05/11] uprobes: Add mapping for optimized uprobe trampolines

[Jiri Olsa]

On Tue, Nov 19, 2024 at 10:13:48AM +0100, Peter Zijlstra wrote:
> On Mon, Nov 18, 2024 at 10:06:51PM -0800, Andrii Nakryiko wrote:
> 
> > > > Jiri, we could also have an option to support 64-bit call, right? We'd
> > > > need nop9 for that, but it's an option as well to future-proofing this
> > > > approach, no?
> > >
> > > hm, I don't think there's call with relative 64bit offset
> > 
> > why do you need a relative, when you have 64 bits? ;) there is a call
> > to absolute address, no?
> 
> No, there is not :/ You get to use an indirect call, which means
> multiple instructions and all the speculation joy.
> 
> IFF USDT thingies have AX clobbered (I couldn't find in a hurry) then
> patching the multi instruction thing is relatively straight forward, if
> they don't, its going to be a pain.

I don't follow, what's the reason for that?

jirka