Re: [PATCH 08/15] x86/alternatives: Teach text_poke_bp() to emulate instructions

From: Josh Poimboeuf
Date: Mon Jun 10 2019 - 13:02:47 EST

On Wed, Jun 05, 2019 at 03:08:01PM +0200, Peter Zijlstra wrote:
> In preparation for static_call support, teach text_poke_bp() to
> emulate instructions, including CALL.
> The current text_poke_bp() takes a @handler argument which is used as
> a jump target when the temporary INT3 is hit by a different CPU.
> When patching CALL instructions, this doesn't work because we'd miss
> the PUSH of the return address. Instead, teach poke_int3_handler() to
> emulate an instruction, typically the instruction we're patching in.
> This fits almost all text_poke_bp() users, except
> arch_unoptimize_kprobe() which restores random text, and for that site
> we have to build an explicit emulate instruction.
> Cc: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
> Cc: Nadav Amit <namit@xxxxxxxxxx>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>

Reviewed-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>