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

[Peter Zijlstra]

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.