Re: [PATCH v2 1/2] arm64: implement FTRACE_WITH_REGS

From	Steven Rostedt <rostedt@goodmis.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH v2 1/2] arm64: implement FTRACE_WITH_REGS
Date	2016-07-08 23:10 +0200
Message-ID	<rSLc6-1Ig-17@gated-at.bofh.it> (permalink)
References	(3 earlier) <rSFzI-6qY-17@gated-at.bofh.it> <rSFT4-6xS-37@gated-at.bofh.it> <rSGcp-6ES-1@gated-at.bofh.it> <rSGm6-6Ir-23@gated-at.bofh.it> <rSKzo-1bN-11@gated-at.bofh.it>
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On Fri, 8 Jul 2016 22:24:55 +0200
Torsten Duwe <duwe@lst.de> wrote:

> On Fri, Jul 08, 2016 at 11:57:10AM -0400, Steven Rostedt wrote:
> > On Fri, 8 Jul 2016 10:48:24 -0500
> > Josh Poimboeuf <jpoimboe@redhat.com> wrote:  
> > > 
> > > Here, with -fprolog-pad, it's already a nop, so no change is needed.
> > >   
> 
> Yes, exactly.
> 
> > That's what I was thinking. But as I stated in another email (probably
> > in the air when you wrote this), the call to ftrace_modify_code() may be
> > completely circumvented by ftrace_make_nop() if the addr is MCOUNT_ADDR.  
> 
> Only on the _first_ invocation. Later on, tracing can be switched on and off,
> and then the instructions need to be changed just like with fentry (or
> profile-kernel ;-)
> 

Understood, but ftrace_modify_code() will only receive addr ==
MCOUNT_ADDR on boot up or when a module is loaded. In both cases, with
-fprolog-pad it will already be a nop, hence no need to call
ftrace_modify_code(), in those cases.

In all other cases, addr will point to a ftrace trampoline.

-- Steve

Thread

[PATCH v2 1/2] arm64: implement FTRACE_WITH_REGS Torsten Duwe <duwe@lst.de> - 2016-06-27 17:20 +0200
  Re: [PATCH v2 1/2] arm64: implement FTRACE_WITH_REGS Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-01 15:00 +0200
    Re: [PATCH v2 1/2] arm64: implement FTRACE_WITH_REGS Torsten Duwe <duwe@lst.de> - 2016-07-04 11:20 +0200
  Re: [PATCH v2 1/2] arm64: implement FTRACE_WITH_REGS Petr Mladek <pmladek@suse.com> - 2016-07-08 17:00 +0200
    Re: [PATCH v2 1/2] arm64: implement FTRACE_WITH_REGS Torsten Duwe <duwe@lst.de> - 2016-07-08 17:10 +0200
      Re: [PATCH v2 1/2] arm64: implement FTRACE_WITH_REGS Petr Mladek <pmladek@suse.com> - 2016-07-08 17:30 +0200
        Re: [PATCH v2 1/2] arm64: implement FTRACE_WITH_REGS Josh Poimboeuf <jpoimboe@redhat.com> - 2016-07-08 17:50 +0200
          Re: [PATCH v2 1/2] arm64: implement FTRACE_WITH_REGS Steven Rostedt <rostedt@goodmis.org> - 2016-07-08 18:00 +0200
            Re: [PATCH v2 1/2] arm64: implement FTRACE_WITH_REGS Torsten Duwe <duwe@lst.de> - 2016-07-08 22:30 +0200
              Re: [PATCH v2 1/2] arm64: implement FTRACE_WITH_REGS Steven Rostedt <rostedt@goodmis.org> - 2016-07-08 23:10 +0200
                Re: [PATCH v2 1/2] arm64: implement FTRACE_WITH_REGS Torsten Duwe <duwe@lst.de> - 2016-07-09 11:10 +0200
                Re: [PATCH v2 1/2] arm64: implement FTRACE_WITH_REGS Steven Rostedt <rostedt@goodmis.org> - 2016-07-15 20:40 +0200
        Re: [PATCH v2 1/2] arm64: implement FTRACE_WITH_REGS Steven Rostedt <rostedt@goodmis.org> - 2016-07-08 17:50 +0200

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