Freebsd-7.4 + std gcc 4.2.1 fails to honour -march=i586
John Baldwin
jhb at freebsd.org
Wed Jul 20 15:15:01 UTC 2011
On Wednesday, July 20, 2011 8:34:57 am Julian H. Stacey wrote:
> Hi,
> Reference:
> > From: John Baldwin <jhb at freebsd.org>
> > Date: Wed, 20 Jul 2011 07:48:05 -0400
> > Message-id: <201107200748.05786.jhb at 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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