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

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Message-ID: <20190510121720.GT2589@hirez.programming.kicks-ass.net>
Date:   Fri, 10 May 2019 14:17:20 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Andy Lutomirski <luto@...capital.net>,
        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 Fri, May 10, 2019 at 12:21:03PM +0900, Masami Hiramatsu wrote:
> Yes, optprobe also has to save and restore the flags.
> Above trampline is for kretprobe, which is placed at the function return, so
> we don't have to care about flags.

Sure, optprobe is actually special here, because it branches out at
'random' places and does indeed need to preserve flags.

But both ftrace and retprobes are at C function call boundaries.
Preserving flags doesn't make sense.