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From: Dimitry Andric <dim@FreeBSD.org>
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To: Peter Wemm <peter@wemm.org>
Subject: Re: UPDATE Re: making use of userland dtrace on FreeBSD
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Cc: "arch@freebsd.org" <arch@freebsd.org>, Adrian Chadd <adrian@freebsd.org>,
 Alfred Perlstein <bright@mu.org>, Rui Paulo <rpaulo@freebsd.org>,
 Alfred Perlstein <alfred@ixsystems.com>
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On 2012-12-27 06:32, Peter Wemm wrote:
> On Wed, Dec 26, 2012 at 8:41 PM, Alfred Perlstein <bright@mu.org> wrote:
...
>> Can you clarify some?  If it was somewhat easy to re-add
>> -fomit-frame-pointer to critical libraries like this, then that would be OK?
>
> No, you can't add MD flags like this.  The way to do it is see things
> like PIC, WARNS, etc where you can do overrides of defaults on a
> directory basis, and respect the system-wide user overrides.
>
> Remember, -fno-omit-frame-pointer is the default on i386 (except at
> high -O levels with gcc, I dont know where clang, the default
> compiler, draws the line).  Other platforms don't even have frame
> pointers.  You can't just scatter that switch around the place.

Just for reference:
- gcc versions < 4.6 always use -fno-omit-frame-pointer for i386,
   and enable -fomit-frame-pointer for amd64, when optimization is
   enabled (-O1 or higher).
- gcc versions >= 4.6 enable -fomit-frame-pointer for both i386 and
   amd64, when optimization is enabled (-O1 or higher).
- clang enables -fomit-frame-pointer only when explicity specified.  I
   will submit a patch to upstream to make it mimic the behaviour of our
   gcc in base, e.g. enable -fomit-frame-pointer only for amd64, when
   optimization is enabled (-O1 or higher).