Re: [PATCH 2/4] x86/kprobes: Fix frame pointer annotations

From: Josh Poimboeuf
Date: Wed May 08 2019 - 14:50:06 EST

On Wed, May 08, 2019 at 05:39:07PM +0200, Peter Zijlstra wrote:
> On Wed, May 08, 2019 at 07:42:48AM -0500, Josh Poimboeuf wrote:
> > On Wed, May 08, 2019 at 02:04:16PM +0200, Peter Zijlstra wrote:
> > > Do the x86_64 variants also want some ORC annotation?
> >
> > Maybe so. Though it looks like regs->ip isn't saved. The saved
> > registers might need to be tweaked. I'll need to look into it.
> What all these sites do (and maybe we should look at unifying them
> somehow) is turn a CALL frame (aka RET-IP) into an exception frame (aka
> pt_regs).
> So regs->ip will be the return address (which is fixed up to be the CALL
> address in the handler).

But from what I can tell, trampoline_handler() hard-codes regs->ip to
point to kretprobe_trampoline(), and the original return address is
placed in regs->sp.

Masami, is there a reason why regs->ip doesn't have the original return
address and regs->sp doesn't have the original SP? I think that would
help the unwinder understand things.