linux-kernel - Re: [PATCH 6/6][RFC] kprobes: Allow probe on ftrace reserved text (but move it)

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Message-ID: <y0mk411mbuz.fsf@fche.csb>
Date:	Fri, 27 Apr 2012 11:29:56 -0400
From:	fche@...hat.com (Frank Ch. Eigler)
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	yrl.pp-manager.tt@...achi.com
Subject: Re: [PATCH 6/6][RFC] kprobes: Allow probe on ftrace reserved text (but move it)

Steven Rostedt <rostedt@...dmis.org> writes:

> [...]
> What do you think of this patch?
> [...]
> +	/*
> +	 * If the address is located on a ftrace nop, set the
> +	 * breakpoint to the following instruction.
> +	 */
> +	ftrace_addr = ftrace_location((unsigned long)addr);
> +	if (unlikely(ftrace_addr)) {
> +		addr = (kprobe_opcode_t *)(ftrace_addr + MCOUNT_INSN_SIZE);
> +		p->flags |= KPROBE_FLAG_MOVED;
> +	}
> [...]

I suspect Masami intended that this flag is later used during int3
processing to subtract MCOUNT_INSN_SIZE back out from the pt_regs->ip
during kprobe_handler() if this flag was set.

- FChE
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