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Date:      Sat, 28 May 2011 20:39:24 +0000
From:      Alexander Best <arundel@freebsd.org>
To:        Bruce Cran <bruce@cran.org.uk>
Cc:        freebsd-hackers@FreeBSD.ORG, freebsd-toolchain@FreeBSD.ORG, Pan Tsu <inyaoo@gmail.com>
Subject:   Re: [rfc] a few kern.mk and bsd.sys.mk related changes
Message-ID:  <20110528203924.GA88186@freebsd.org>
In-Reply-To: <20110528202619.GA27204@muon.cran.org.uk>
References:  <20110527115147.GA73802@freebsd.org> <3BF63174-1B29-4A4D-96DD-3ED65ED96EAC@bsdimp.com> <20110527181459.GA29908@freebsd.org> <20110527182906.GA31871@freebsd.org> <86oc2mlsey.fsf@gmail.com> <20110528182326.GA75447@freebsd.org> <20110528202619.GA27204@muon.cran.org.uk>

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On Sat May 28 11, Bruce Cran wrote:
> On Sat, May 28, 2011 at 06:23:26PM +0000, Alexander Best wrote:
> > 
> > well i'm not an expert on this. but are we 100% sure that a kernel on amd64
> > compiled with -O2 frename-registers can be debugged the same way as one with
> > -O? if that is the case: sure...-O2 is fine. ;)
> > 
> > however i've often read messages - mostly by bruce evans - claiming that
> > anything greater than -O will in fact decrease a kernel's ability to be
> > debugged just as well as a kernel with -O.
> > 
> 
> The critical option when -O2 is used is -fno-omit-frame-pointers, since removing
> frame pointers makes debugging impossible (on i386). With -O2 code is moved around and
> removed, so debugging is more difficult, but can still provide useful
> information.

how about making -fno-omit-frame-pointers mandatory for all builds with an
optimisation level higher than -O?

something like

.if !empty(COPTFLAGS:M-O[234sz]) && empty(COPTFLAGS:M-fno-omit-frame-pointers)
COPTFLAGS+= -fno-omit-frame-pointers
.endif

(-O4 and -Oz are clang specific, but it won't hurt having them in there)

cheers.
alex

> 
> -- 
> Bruce Cran

-- 
a13x



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