linux-kernel - Re: [RFC PATCH 0/8] uprobe/x86: Add support to optimize prologue

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Message-Id: <20251208153056.3a4e9cd3511ccf00dc12e265@kernel.org>
Date: Mon, 8 Dec 2025 15:30:56 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Oleg Nesterov <oleg@...hat.com>
Cc: Jiri Olsa <jolsa@...nel.org>, Masami Hiramatsu <mhiramat@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>, Andrii Nakryiko <andrii@...nel.org>,
 bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, x86@...nel.org, Song Liu
 <songliubraving@...com>, Yonghong Song <yhs@...com>, John Fastabend
 <john.fastabend@...il.com>, Steven Rostedt <rostedt@...dmis.org>, Ingo
 Molnar <mingo@...nel.org>, David Laight <David.Laight@...lab.com>
Subject: Re: [RFC PATCH 0/8] uprobe/x86: Add support to optimize prologue

On Mon, 24 Nov 2025 19:12:42 +0100
Oleg Nesterov <oleg@...hat.com> wrote:

> On 11/17, Jiri Olsa wrote:
> >
> > This patchset adds support to optimize uprobe on top of instruction
> > that could be emulated and also adds support to emulate particular
> > versions of mov and sub instructions to cover some of the user space
> > functions prologues, like:
> >
> >   pushq %rbp
> >   movq  %rsp,%rbp
> >   subq  $0xb0,%rsp
> 
> ...
> 
> > There's an additional issue that single instruction replacement does
> > not have and it's the possibility of the user space code to jump in the
> > middle of those 5 bytes. I think it's unlikely to happen at the function
> > prologue, but uprobe could be placed anywhere. I'm not sure how to
> > mitigate this other than having some enable/disable switch or config
> > option, which is unfortunate.
> 
> plus this breaks single-stepping... Although perhaps we don't really care.

Yeah, and I think we can stop optimization if post_handler is set.

Thanks,

-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>