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Date: Sat, 28 May 2011 21:32:44 +0000
From: Alexander Best <arundel@freebsd.org>
To: Bruce Cran <bruce@cran.org.uk>
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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
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On Sat May 28 11, Alexander Best wrote:
> 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?

man this is confusing. why must the freebsd make skeleton be so complicated. :(
it seems -fno-omit-frame-pointers gets set in sys/conf/Makefile.amd64 and
sys/conf/Makefile.powerpc already. also for modules in sys/conf/kmod.mk. i
guess somebody with a better in deth knowledge should investigate this matter.

this is a bit too complicated for me.

cheers.
alex

> 
> 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

-- 
a13x