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

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Date:   Tue, 7 May 2019 18:34:40 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Steven Rostedt <rostedt@...dmis.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>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: Re: [RFC][PATCH 1/2] x86: Allow breakpoints to emulate call functions

On Tue, May 07, 2019 at 08:31:14AM -0700, Linus Torvalds wrote:
> The reality is that changing something fundamental like the kernel
> stack at this point for an architecture that will not change in the
> future is silly.

In my eyes it makes sense because i386 is a minority architecture at
this point, and 'nobody' wants to care about how its different if they
don't have to.

> The reality is that Peter's patch is much bigger than mine, because it
> needed a lot of other changes *because* it did that change.

Yes, I change the way stack layout works on i386, and yes that affects a
lot of code. _However_ all of that code is now more like x86_64 than it
was.

Earlier you said that kernel_stack_pointer() was a horrible thing; and
most/all the code that I ended up touching was similarly horrible.

Would you consider my approach later on, under the guise of unification?
We can work on it for a while, and make sure all the iffy bits are
sorted, no need to rush?