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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Mon, 6 May 2019 20:28:53 -0700
Message-ID: <CAHk-=wi4vPg4pu6RvxQrUuBL4Vgwd2G2iaEJVVumny+cBOWMZw@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>,
        Ingo Molnar <mingo@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
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On Mon, May 6, 2019 at 8:22 PM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> But still, we need to emulate the call, which requires pushing the
> return code back onto the stack. I believe that part is the part we are
> struggling with.

Yes. But I was looking at the ftrace parts because I didn't see the
bug in the low-level x86 side, so...

The x86 int3 faulting code itself looks so *trivially* simple, and it
does work for the trivial test-case too. Which was what made me go
"Hmm, maybe there's timing or something".

But it could obviously also be that the trivial test-case is just too
trivial, and doesn't involve nmi etc etc.

               Linus