Date: Wed, 20 Jul 2011 11:13:51 -0400 From: John Baldwin <jhb@freebsd.org> To: "Julian H. Stacey" <jhs@berklix.com> Cc: freebsd-hackers@freebsd.org, hackers@freebsd.org, Dan Nelson <dnelson@allantgroup.com> Subject: Re: Freebsd-7.4 + std gcc 4.2.1 fails to honour -march=i586 Message-ID: <201107201113.52085.jhb@freebsd.org> In-Reply-To: <201107201235.p6KCYvmT007475@fire.js.berklix.net> References: <201107201235.p6KCYvmT007475@fire.js.berklix.net>
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On Wednesday, July 20, 2011 8:34:57 am Julian H. Stacey wrote: > Hi, > Reference: > > From: John Baldwin <jhb@freebsd.org> > > Date: Wed, 20 Jul 2011 07:48:05 -0400 > > Message-id: <201107200748.05786.jhb@freebsd.org> > > John Baldwin wrote: > > On Wednesday, July 20, 2011 7:33:26 am Julian H. Stacey wrote: > > > What should FreeBSD do ? > > > Add a comment to man gcc ... that -march=i586 is not > > > enough, & feed the comment back to gcc project & see how > > > they want to handle it ? > > > > No, this is not a GCC bug. If you want to use a single build machine that > > will compile programs for other machines on a network to use, it must use the > > lowest common denominator for its CPUTYPE in /etc/make.conf. > > > > The out-of-the-box crt files from a FreeBSD install will work fine on a 486 > > and above, so can only get yourself into this quandry by building a new world > > with a CPUTYPE (or similar CFLAGS) setting in /etc/make.conf that violates > > this rule. > > > > You can fix your machine by fixing the CPUTYPE in your build machine and > > building and installing a new world (do use NO_CLEAN=yes for your build, do a > > full build). You will also want to rebuild any other binaries on this machine > > that you share with other machines. > > > > -- > > John Baldwin > > > Hi John, > Yes I realise all that now thanks. > The point now is man gcc is misleading/ incomplete: > "-march=cpu-type > Generate instructions for the machine type cpu-type." > Those instructions will not make a program that runs on a lesser CPU type > without alternate crt for lesse CPU. > > CFLAGS in make.conf is fine for single developer/ host debugging, > but is not appropriate for multi user multi make builds os src/ ports/ other > > Its seems just that gcc -march fails to select alternate crt. > > One gross ugly solution needing root would be to create chroots, > but Too ugly. > > I suggest gcc via -march should also be used as a selection for sub > dirs for crt ? & we should co-operate with gcc project on that, > *BSD & *linux must all face same phenomena so lets not develop > a non standard solution. I think this is a harder problem than you expect. It is not just the crt files that matter, but every library. You would need CPU-specific versions of every static library on the build system, and possibly you would want to do this for all shared libraries too. -- John Baldwin
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