linux-kernel - Re: [RFC perf/core 05/11] uprobes: Add mapping for optimized uprobe trampolines

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Message-ID: <ZypI3n-2wbS3_w5p@krava>
Date: Tue, 5 Nov 2024 17:33:34 +0100
From: Jiri Olsa <olsajiri@...il.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Oleg Nesterov <oleg@...hat.com>, Andrii Nakryiko <andrii@...nel.org>,
	bpf@...r.kernel.org, Song Liu <songliubraving@...com>,
	Yonghong Song <yhs@...com>,
	John Fastabend <john.fastabend@...il.com>,
	Hao Luo <haoluo@...gle.com>, Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Alan Maguire <alan.maguire@...cle.com>,
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [RFC perf/core 05/11] uprobes: Add mapping for optimized uprobe
 trampolines

On Tue, Nov 05, 2024 at 03:23:27PM +0100, Peter Zijlstra wrote:
> On Tue, Nov 05, 2024 at 02:33:59PM +0100, Jiri Olsa wrote:
> > Adding interface to add special mapping for user space page that will be
> > used as place holder for uprobe trampoline in following changes.
> > 
> > The get_tramp_area(vaddr) function either finds 'callable' page or create
> > new one.  The 'callable' means it's reachable by call instruction (from
> > vaddr argument) and is decided by each arch via new arch_uprobe_is_callable
> > function.
> > 
> > The put_tramp_area function either drops refcount or destroys the special
> > mapping and all the maps are clean up when the process goes down.
> 
> In another thread somewhere, Andrii mentioned that Meta has executables
> with more than 4G of .text. This isn't going to work for them, is it?
> 

not if you can't reach the trampoline from the probed address

jirka