linux-kernel - Re: [PATCH -tip v2 3/9] ftrace/x86: Support SAVE

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Message-ID: <20120605212411.GC11575@redhat.com>
Date:	Tue, 5 Jun 2012 17:24:11 -0400
From:	"Frank Ch. Eigler" <fche@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	yrl.pp-manager.tt@...achi.com
Subject: Re: [PATCH -tip v2 3/9] ftrace/x86: Support SAVE_REGS feature on i386

Hi -

On Tue, Jun 05, 2012 at 04:37:46PM -0400, Steven Rostedt wrote:
> [...]
> I'm not sure we really need to restore all the regs. I'll keep this for
> now, but for an optimization, we can just restore the ones that mcount
> mcount needs to.
> 
> Or do you expect kprobes to change any of theses?

That would be the way for a kprobe to modify variables/values that
happen to be in the registers.  In systemtap, for example:

# stap -g -e 'probe kernel.function("foo") { $bar = 1 }'

- FChE
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