linux-kernel - Re: [PATCH -v4 4/9] tracing: add static function tracer support for MIPS

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Date:	Fri, 23 Oct 2009 09:09:06 +0800
From:	Wu Zhangjin <wuzhangjin@...il.com>
To:	rostedt@...dmis.org
Cc:	Adam Nemet <anemet@...iumnetworks.com>,
	David Daney <ddaney@...iumnetworks.com>,
	Richard Sandiford <rdsandiford@...glemail.com>,
	linux-kernel@...r.kernel.org, linux-mips@...ux-mips.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Nicholas Mc Guire <der.herr@...r.at>
Subject: Re: [PATCH -v4 4/9] tracing: add static function tracer support
 for MIPS

On Thu, 2009-10-22 at 17:55 -0400, Steven Rostedt wrote:
> On Thu, 2009-10-22 at 14:29 -0700, Adam Nemet wrote:
> > Steven Rostedt writes:
> > > On Thu, 2009-10-22 at 13:30 -0700, Adam Nemet wrote:
> > > > Also note that for functions invoked via tail call you won't get an exit
> > > > event.  E.g. if bar is tail-called from foo:
> > > > 
> > > >   foo entered
> > > >   bar entered
> > > >   foo/bar exited
> > > > 
> > > > However, this is not MIPS-specific and you can always disable tail calls
> > > > with -fno-optimize-sibling-calls.
> > > 
> > > The question is, would bar have a _mcount call? So far, we have not had
> > > any issues with this on either x86 nor PPC.
> > 
> > Yes, bar will have an _mcount call.  The difference is that bar will return to
> > foo's caller directly rather than to foo first.
> 
> I guess the best bet is to have CONFIG_FUNCTION_GRAPH enable
> -fno-optimize-sibling-calls and be done with it.
> 

Hello, This did for us:

Makefile:

ifdef CONFIG_FRAME_POINTER
KBUILD_CFLAGS   += -fno-omit-frame-pointer -fno-optimize-sibling-calls
else
KBUILD_CFLAGS   += -fomit-frame-pointer
endif

So, the only thing we need to do is enabling CONFIG_FRAME_POINTER.
Seems it was selected by FTRACE by default.

Regards,
	Wu Zhangjin

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