linux-kernel - Re: [PATCH 2/4] x86/kprobes: Fix frame pointer annotations

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Message-ID: <20190509182622.GB2623@hirez.programming.kicks-ass.net>
Date:   Thu, 9 May 2019 20:26:22 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Nicolai Stange <nstange@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Shuah Khan <shuah@...nel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Juergen Gross <jgross@...e.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nayna Jain <nayna@...ux.ibm.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Joerg Roedel <jroedel@...e.de>, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH 2/4] x86/kprobes: Fix frame pointer annotations

On Thu, May 09, 2019 at 01:37:42PM -0400, Steven Rostedt wrote:
> On Thu, May 09, 2019 at 10:14:31AM +0200, Peter Zijlstra wrote:
> > 
> > Right; I already fixed that in my patch changing i386's pt_regs.
> > 
> > But what I'd love to do is something like the belwo patch, and make all
> > the trampolines (very much including ftrace) use that. Such that we then
> > only have 1 copy of this magic (well, 2 because x86_64 also needs an
> > implementation of this of course).
> > 
> > Changing ftrace over to this would be a little more work but it can
> > easily chain things a little to get its original context back:
> > 
> > ENTRY(ftrace_regs_caller)
> > GLOBAL(ftrace_regs_func)
> > 	push ftrace_stub
> > 	push ftrace_regs_handler
> 
> Note, ftrace_stub is dynamically modified to remove any indirect calls.

Yeah, I realized that a few hours after I send this out; as you might
have seen by the IRC chatter on this.

Still, maybe we can wrap the thing in a .macro and reuse things that
way. Because I really hate there are at least 3 (x2 for x86_64) copies
of this around.