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    SubjectRe: [RFC][PATCH 1/2] x86: Allow breakpoints to emulate call functions
    On Tue, May 07, 2019 at 08:27:16AM -0400, Steven Rostedt wrote:
    > On Tue, 7 May 2019 11:27:31 +0200
    > Peter Zijlstra <peterz@infradead.org> wrote:
    >
    > > FWIW, both these trampolines assume a kprobe will not
    > > int3_emulate_{push/call}(), for both bitnesses.
    > >
    > > But then; I'm thinking kprobes should be inspection only and not modify
    > > things. So that might just be good enough.
    >
    > I believe there are kprobe calls that do modify things. Note, they can
    > modify regs->ip.

    The kprobe pre_handler as used by kretprobes does, and that is indeed
    handled by the trampolines.

    > Kprobes sets the FTRACE_OPS_FL_IPMODIFY flag, thus
    > they can never be put at the same location that is being live patched.

    OK, so do we want to allow kprobes that also modify regs->sp ? Because
    then we need to change these trampolines a bit.

    I'd prefer not to allow kprobes this.

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