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

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Date:	Mon, 14 Jul 2014 23:18:41 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Josh Poimboeuf <jpoimboe@...hat.com>,
	Jiri Kosina <jkosina@...e.cz>,
	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>,
	"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

2014-07-14 (월), 17:18 +0900, Masami Hiramatsu:
> (2014/07/14 16:16), Namhyung Kim wrote:
> > Hi Masami,
> > 
> > On Mon, 14 Jul 2014 10:35:21 +0900, Masami Hiramatsu wrote:
> >> (2014/07/11 23:29), Josh Poimboeuf wrote:
> >>> Here's the same stack trace with this patch:
> >>>
> >>>   [ 1314.612287]  [<ffffffff81700312>] dump_stack+0x45/0x56
> >>>   [ 1314.612290]  [<ffffffff8125f5b0>] ? meminfo_proc_open+0x30/0x30
> >>>   [ 1314.612293]  [<ffffffffa080a494>] kpatch_ftrace_handler+0x14/0xf0 [kpatch]
> >>>   [ 1314.612306]  [<ffffffffa00160c4>] 0xffffffffa00160c3
> >>
> >> Here, this still has a wrong entry. Maybe the trampline doesn't setup
> >> frame pointer (bp) correctly.
> > 
> > Hmm.. are you saying about the hex address above?  I guess it's a valid
> > entry in the (dynamic) trampoline, but has no symbol..
> 
> Ah, indeed. (BTW, why is it one less than the address ...? printk's spec?)

Argh, it seems like a bug in printk's %pB format processing.. :-/

It subtract 1 from the address for stacktrace.  Please see the commit
0f77a8d37825 ("vsprintf: Introduce %pB format specifier") and
71f9e59800e5 ("x86, dumpstack: Use %pB format specifier for stack
trace") for details.  But it should restore the original address when it
failed to find a symbol for that address.

I'll send a fix soon.

Thanks,
Namhyung


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