linux-kernel - Re: [RFC][PATCH 0/3] ftrace: Add dynamically allocated trampolines

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Message-ID: <20140708102416.50d996e2@gandalf.local.home>
Date:	Tue, 8 Jul 2014 10:24:16 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Namhyung Kim <namhyung@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>, Oleg Nesterov <oleg@...hat.com>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Seth Jennings <sjenning@...hat.com>,
	Jiri Slaby <jslaby@...e.cz>
Subject: Re: [RFC][PATCH 0/3] ftrace: Add dynamically allocated trampolines

On Mon, 7 Jul 2014 15:22:27 +0200 (CEST)
Jiri Kosina <jkosina@...e.cz> wrote:

> On Fri, 4 Jul 2014, Steven Rostedt wrote:
> 
> > Well, I guess the answer to that is what do you consider the trampoline? 
> > I'm currently considering it to be the assembly code that the 
> > mcount/fentry call jumps to. We only have two trampolines (three if you 
> > count the function graph code that will be called directly come 3.17). 
> > Those two are the normal ftrace_caller and the ftrace_regs_caller. 
> 
> BTW, on those archs that support regs saving already, is there really a 
> reson not to kill ftrace_caller and keep just ftrace_regs_caller?
> 

Consistency. Perhaps the two can be the same trampoline, which would be
trivial to implement, but I wouldn't kill one which would make the
generic code more complex.

-- Steve
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