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

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Message-ID: <aSSgGu8X04XoYN8D@redhat.com>
Date: Mon, 24 Nov 2025 19:12:42 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Jiri Olsa <jolsa@...nel.org>
Cc: 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 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.

Oleg.