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

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Date:	Fri, 11 Jul 2014 11:26:34 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Josh Poimboeuf <jpoimboe@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	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>,
	Seth Jennings <sjenning@...hat.com>,
	Jiri Slaby <jslaby@...e.cz>
Subject: Re: [RFC][PATCH 0/3] ftrace: Add dynamically allocated trampolines

(2014/07/11 6:44), Jiri Kosina wrote:
> On Thu, 10 Jul 2014, Josh Poimboeuf wrote:
> 
>> I did some testing with kpatch and I found one minor issue.  The dynamically
>> allocated trampoline seems to confuse dump_stack() somewhat.
>>
>> I added a dump_stack() call in my ftrace_ops callback function
>> (kpatch_ftrace_handler) which had a filter on meminfo_proc_show().
> 
> Interesting. Are you using dwarf2 unwinder for stack dumping by any 
> chance? It seems to get things right here. Will look into it more 
> tomorrow.

Hmm, can dwarf2 unwinder work on the trampoline method?
Since the trampoline just a copy of instructions which
will not have CFI(which is stored in dwarf section),
I guess it may not work...
Frame pointer (push bp and save sp to bp on the entry) can
work anyway.

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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