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Groups > linux.kernel > #1470247

Re: livepatch/kprobes incompatibility

From Josh Poimboeuf <jpoimboe@redhat.com>
Newsgroups linux.kernel
Subject Re: livepatch/kprobes incompatibility
Date 2016-08-25 18:10 +0200
Message-ID <sa5o5-3eV-23@gated-at.bofh.it> (permalink)
References <s9v1f-3wp-3@gated-at.bofh.it> <s9CYO-op-11@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On Wed, Aug 24, 2016 at 11:39:59AM +0200, Petr Mladek wrote:
>   + kretprobe is safe as well; the kprobe handler does not modify regs->ip;
>     it just modifies the return address from the function; it does not affect
>     livepatching because the address is defined by the function caller
>     and livepatching keeps it as is

BTW, I think there's still a kretprobe issue which affects the accuracy
of the unwinder and the consistency model.  The unwinder will report
kretprobe_trampoline instead of the real caller's return address.

It can probably be fixed similarly to how ftrace function_graph tracing
does it with a ftrace_graph_ret_addr() helper:

  https://lkml.kernel.org/r/cover.1471607358.git.jpoimboe@redhat.com

-- 
Josh

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Thread

livepatch/kprobes incompatibility Jessica Yu <jeyu@redhat.com> - 2016-08-24 03:20 +0200
  Re: livepatch/kprobes incompatibility Petr Mladek <pmladek@suse.com> - 2016-08-24 11:50 +0200
    Re: livepatch/kprobes incompatibility Masami Hiramatsu <mhiramat@kernel.org> - 2016-08-24 17:30 +0200
    Re: livepatch/kprobes incompatibility Josh Poimboeuf <jpoimboe@redhat.com> - 2016-08-25 18:10 +0200
  Re: livepatch/kprobes incompatibility Masami Hiramatsu <mhiramat@kernel.org> - 2016-08-24 17:20 +0200

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