Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 7 May 2019 18:34:40 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Nicolai Stange <nstange@suse.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        the arch/x86 maintainers <x86@kernel.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Jiri Kosina <jikos@kernel.org>,
        Miroslav Benes <mbenes@suse.cz>,
        Petr Mladek <pmladek@suse.com>,
        Joe Lawrence <joe.lawrence@redhat.com>,
        Shuah Khan <shuah@kernel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Mimi Zohar <zohar@linux.ibm.com>,
        Juergen Gross <jgross@suse.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Nayna Jain <nayna@linux.ibm.com>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Joerg Roedel <jroedel@suse.de>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@vger.kernel.org>, stable <stable@vger.kernel.org>,
        Masami Hiramatsu <mhiramat@kernel.org>
Subject: Re: [RFC][PATCH 1/2] x86: Allow breakpoints to emulate call functions
Message-ID: <20190507163440.GV2606@hirez.programming.kicks-ass.net>
References: <CAHk-=whZwqzbu-=1r_j_cXfd=ta1q7RFCuneqBZfQQhS_P-BmQ@mail.gmail.com>
 <20190506215353.14a8ef78@oasis.local.home>
 <CAHk-=wjLXmOn=Cp=uOfO4gE01eN_-UcOUyrMTTw5-f_OfPO48Q@mail.gmail.com>
 <20190506225819.11756974@oasis.local.home>
 <CAHk-=wh4FCNBLe8OyDZt2Tr+k9JhhTsg3H8R4b55peKcf0b6eQ@mail.gmail.com>
 <20190506232158.13c9123b@oasis.local.home>
 <CAHk-=wi4vPg4pu6RvxQrUuBL4Vgwd2G2iaEJVVumny+cBOWMZw@mail.gmail.com>
 <CAHk-=wg2_okyU8mpkGCUrudgfg8YmNetSD8=scNbOkN+imqZdQ@mail.gmail.com>
 <20190507111227.1d4268d7@gandalf.local.home>
 <CAHk-=wjYdj+vvV8uUA8eaUSxOhu=xuQxdo-dtM927j0-3hSkEw@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAHk-=wjYdj+vvV8uUA8eaUSxOhu=xuQxdo-dtM927j0-3hSkEw@mail.gmail.com>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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?