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

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Date:   Wed, 8 May 2019 13:48:48 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     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,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [PATCH 2/4] x86/kprobes: Fix frame pointer annotations

On Wed, May 08, 2019 at 05:39:07PM +0200, Peter Zijlstra wrote:
> On Wed, May 08, 2019 at 07:42:48AM -0500, Josh Poimboeuf wrote:
> > On Wed, May 08, 2019 at 02:04:16PM +0200, Peter Zijlstra wrote:
> 
> > > Do the x86_64 variants also want some ORC annotation?
> > 
> > Maybe so.  Though it looks like regs->ip isn't saved.  The saved
> > registers might need to be tweaked.  I'll need to look into it.
> 
> What all these sites do (and maybe we should look at unifying them
> somehow) is turn a CALL frame (aka RET-IP) into an exception frame (aka
> pt_regs).
> 
> So regs->ip will be the return address (which is fixed up to be the CALL
> address in the handler).

But from what I can tell, trampoline_handler() hard-codes regs->ip to
point to kretprobe_trampoline(), and the original return address is
placed in regs->sp.

Masami, is there a reason why regs->ip doesn't have the original return
address and regs->sp doesn't have the original SP?  I think that would
help the unwinder understand things.

-- 
Josh