Freebsd-7.4 + std gcc 4.2.1 fails to honour -march=i586

[John Baldwin]

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