linux-kernel - Re: [RFC][PATCH 1/2] x86: Allow breakpoints to emulate call functions

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Message-Id: <20190508021551.ca791c725cbddc2db541273f@kernel.org>
Date:   Wed, 8 May 2019 02:15:51 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...capital.net>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.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>,
        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>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>, stable <stable@...r.kernel.org>
Subject: Re: [RFC][PATCH 1/2] x86: Allow breakpoints to emulate call
 functions

On Tue, 7 May 2019 23:13:40 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

> On Mon, 6 May 2019 17:45:11 -0400
> Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> > If we go with Peter's patch, I can make this code much more sane, and
> > not have to worry about having &regs->sp be at the top of the stack. I
> > could simply, just push everything in the order of pt_regs and call the
> > handler.
> 
> Hi Steve, I need to catch up with the origin of this series, but it seems
> also good to optprobe which is doing similar trick on pt_regs. If we can
> assume that int3 pt_regs can have a gap, optprobe can also make a gap, and
> it can be also used for storing destination address.

Sorry, I misunderstood. I see the issue ( https://lkml.org/lkml/2019/5/1/497 )
and solutions on the thread. If we really need to fix this trace-livepatch
combination issue, it may be good to backport to stable trees.
>From this viewpoint, Linus's suggestion (no pt_reg changes on x86-32) seems
to have a point.

BTW, even though I think Peter's patch (unifying pt_regs behavior) will also
be good for us for more general reason (not only for fixing actual issue).

Thank you,

-- 
Masami Hiramatsu <mhiramat@...nel.org>