linux-kernel - Re: [PATCH 4/5 v3] ftrace/x86_32: Clean up ftrace_regs

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Message-ID: <20170316155006.1f0ef5fe@gandalf.local.home>
Date:   Thu, 16 Mar 2017 15:50:06 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...capital.net>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH 4/5 v3] ftrace/x86_32: Clean up ftrace_regs_caller

On Thu, 16 Mar 2017 12:30:25 -0700
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Thu, Mar 16, 2017 at 12:24 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> >         popl    %ds
> >         popl    %es
> >         popl    %fs
> >         popl    %gs  
> 
> Do you even need these? Can they be changed by ftrace?

ftrace no, kprobes, maybe.

> 
> And see the previous email about not touching the original location at
> all, adn just duplicating that entry, avoiding all the need for
> shuffling. I *really* hope that ftrace doesn't depend on changing the
> return %eip on the stack. That would be truly nasty.

How do you think the live patching works?

-- Steve