linux-kernel - Re: [RFC][PATCH v3] ftrace/x86_64: Emulate call function while updating in breakpoint handler

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Message-ID: <20190501185726.GR7905@worktop.programming.kicks-ass.net>
Date:   Wed, 1 May 2019 20:57:26 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Andy Lutomirski <luto@...nel.org>,
        Nicolai Stange <nstange@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        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 List Kernel Mailing <linux-kernel@...r.kernel.org>,
        live-patching@...r.kernel.org,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>
Subject: Re: [RFC][PATCH v3] ftrace/x86_64: Emulate call function while
 updating in breakpoint handler

On Wed, May 01, 2019 at 11:01:07AM -0700, Linus Torvalds wrote:
> This looks sane to me, although I'm surprised that we didn't already
> have an annotation for the nonstandard stack frame for asm files. That
> probably would be cleaner in a separate commit, but I guess it doesn't
> matter.
> 
> Anyway, I'm willing to consider the entry code version if it looks a
> _lot_ simpler than this (so I'd like to see them side-by-side), but
> it's not like this looks all that complicated to me either.

So I posted one earlier today:

  https://lkml.kernel.org/r/20190501131117.GW2623@hirez.programming.kicks-ass.net

it's about a 1/3rd the number of lines and has 32bit support. It also
provides all the bits required to implement static_call().

That is; I think I'm firmly in favour of the entry variant -- provided
it actually works of course.