linux-kernel - Re: [RFC][PATCH 1/3] ftrace/x86: Add dynamic allocated trampoline for ftrace

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Message-ID: <53B6ACFC.3090300@hitachi.com>
Date:	Fri, 04 Jul 2014 22:32:44 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	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>,
	Jiri Kosina <jkosina@...e.cz>,
	Seth Jennings <sjenning@...hat.com>,
	Jiri Slaby <jslaby@...e.cz>
Subject: Re: [RFC][PATCH 1/3] ftrace/x86: Add dynamic allocated trampoline
 for ftrace_ops

(2014/07/04 5:07), Steven Rostedt wrote:
> +
> +void arch_ftrace_update_trampoline(struct ftrace_ops *ops)
> +{
> +	unsigned char *new;
> +	unsigned long start_offset;
> +	unsigned long call_offset;
> +	unsigned long offset;
> +	unsigned long ip;
> +	int ret;
> +
> +	if (ops->trampoline) {
> +		/*
> +		 * The ftrace_ops caller may set up its own trampoline.
> +		 * In such a case, this code must not modify it.
> +		 */
> +		if (!(ops->flags & FTRACE_OPS_FL_ALLOC_TRAMP))
> +			return;

Just a question, what happen if the ftrace_ops caller sets up a trampoline which is
not compatible to the ftrace's trampoline, and the ftrace_ops conflicts on a IP with other
ftrace_ops? I guess in that case ftrace will use the loop callback on the IP, but since
the trampoline is not compatible, the result will not be same, is that right? :)

Thank you,

-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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