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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Mon, 6 May 2019 13:44:52 -0700
Message-ID: <CAHk-=wgsi+FQN6bnued8K4KQ2fF53k0JW4TUY+q0XOJyiULXmw@mail.gmail.com>
Subject: Re: [RFC][PATCH 1/2] x86: Allow breakpoints to emulate call functions
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
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        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
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On Mon, May 6, 2019 at 1:42 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> What *can* make sense is "Oh, I'm emulating a call, but I know that
> call will be rewritten, so let me emulate the call and then
> short-circuit the emulation immediately".

That made no sense. The end should have been "and then short-circuit
the _rewriting_ immediately" of course.

The "emulate a call" is just to make the "struct pt_regs" state look
like it would have after the call. The "short circuit the rewriting"
part is the thing that then rewrites the actual instruction based on
that pt_regs state.

                 Linus