Re: RFC: How to handle function tracing, frame pointers and -mfentry?

From: Steven Rostedt <rostedt@goodmis.org>
To: "H. Peter Anvin" <hpa@linux.intel.com>
Cc: Sam Ravnborg <sam@ravnborg.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-kbuild <linux-kbuild@vger.kernel.org>,
	Michal Marek <mmarek@suse.cz>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andi Kleen <andi@firstfloor.org>, Ingo Molnar <mingo@elte.hu>,
	Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: RFC: How to handle function tracing, frame pointers and -mfentry?
Date: Fri, 27 Apr 2012 16:57:39 -0400	[thread overview]
Message-ID: <1335560259.28106.234.camel@gandalf.stny.rr.com> (raw)
In-Reply-To: <4F9B020B.9050205@linux.intel.com>

On Fri, 2012-04-27 at 13:31 -0700, H. Peter Anvin wrote:
> On 04/27/2012 01:27 PM, Sam Ravnborg wrote:
> >>
> >> My question is, how do I remove the dependency in kconfig based on the
> >> compiler?
> > 
> > Allow the user to select one of:
> > 1) function tracer
> > 2) frame pointer
> > 3) none of the above
> > 
> > This should be trivial to do in Kconfig language.
> > 
> > If "function tracer" is selected then use -mfentry if supported,
> > with a fallback to frame pointers.
> > 
> > This looks simple IMO and should be easy to implement too.
> > 
> 
> Except it is the wrong thing.  This is not the only user of frame
> pointer.  What I think you mean is remove the dependency in Kconfig, but
> force the frame pointer enabled if -mfentry is not supported.

You mean option 3?

3) Add frame pointers silently if gcc fails to build with gcc -pg.

Which I should have added, relies on the same thing as option 2:

2) Remove the select entirely.

-- Steve