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

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Date:	Thu, 22 Oct 2009 17:55:17 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Adam Nemet <anemet@...iumnetworks.com>
Cc:	David Daney <ddaney@...iumnetworks.com>, wuzhangjin@...il.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 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.

-- Steve


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