Re: [RFC][PATCH 1/2] x86: Allow breakpoints to emulate call functions

From: Linus Torvalds
Date: Fri May 03 2019 - 14:58:14 EST

On Fri, May 3, 2019 at 9:21 AM Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> So hereâs a somewhat nutty suggestion: how about we tweak the 32-bit entry code to emulate the sane 64-bit frame, not just for int3 but always?

What would the code actually end up looking like? I don't necessarily
object, since that kernel_stack_pointer() thing certainly looks
horrible, but honestly, my suggestion to just pass in the 'struct
pt_regs' and let the call emulation fix it up would have also worked,
and avoided that bug (and who knows what else might be hiding).

I really think that you're now hitting all the special case magic
low-level crap that I wanted to avoid.