Date: Tue, 31 May 2011 10:46:39 +0000 From: Alexander Best <arundel@freebsd.org> To: Dimitry Andric <dim@FreeBSD.org> 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: <20110531104639.GA4218@freebsd.org> In-Reply-To: <4DE4C4CC.4020905@FreeBSD.org> 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> <20110531095742.GA99888@freebsd.org> <4DE4C4CC.4020905@FreeBSD.org>
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On Tue May 31 11, Dimitry Andric wrote: > On 2011-05-31 11:57, Alexander Best wrote: > ... > >>>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. > >any reason we cannot use -O2 -fno-omit-frame-pointers -fno-strict-aliasing > >as > >standard COPTFLAGS with debugging enabled for *all* archs? > > Most likely, the performance gain from -O2 is rather small, except for > special cases, but the pain during debugging is increased a great deal. > > Even if you add frame pointers, with -O2 large pieces of code can be > transformed, variables or even entire functions can be completely > eliminated, and so on, making debugging much more difficult. *lol* we're moving in circles. so back to the beginning: why not use -O for all archs, if debugging was enabled? for amd64 -O2 is always set, no matter, if debugging is enabled or disabled. cheers. alex -- a13x
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