Re: Release Building and /etc/make.conf

On Tuesday 20 January 2004 09:41 am, Bruce Evans wrote:
> On Mon, 19 Jan 2004, Ruslan Ermilov wrote:
> > On Mon, Jan 19, 2004 at 06:23:30PM +1100, Chris Knight wrote:
> > > Howdy,
> > >
> > > I'm just doing a release build of 5.2 and have noticed that
> > > from Stage 4.2 onwards, -mcpu=pentiumpro is added to the cc
> > > command line.
> > > The only place I can see this being set is in /etc/make.conf
> > > which is outside the sandbox.
> > > I was expecting the release build to be CPU agnostic, but
> > > this doesn't appear to be the case. Any way of overriding
> > > this without modifying /etc/make.conf?
>
> Is there a problem with modifying /etc/make.conf?   As maxim said,
> you can avoid /etc/make.conf using __MAKE_CONF.  You can also set
> CPUTYPE in the environment.  Beware that settings in the enviroment
> might not have precedence over settings in /etc/make.conf.  Anyway,
> -mcpu=pentiumpro is not actually set in /etc/make.conf.  As ru doesn't
>
> quite say, it is set in bsd.cpu.mk:
> > There's a substantional difference between -mcpu and -march:
> > : -mcpu=cpu type
> > :        Assume  the defaults for the machine type CPU TYPE when schedul-
> > :        ing instructions.  The choices for CPU  TYPE  are:  i386,  i486,
> > :        i586  (pentium),  pentium,  i686  (pentiumpro),  and pentiumpro.
> > :        While picking a specific CPU TYPE will schedule things appropri-
> > :        ately  for  that particular chip, the compiler will not generate
> >
> >                                            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> >
> > :        any code that does not run on the i386  without  the  -march=cpu
> >
> >          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> >
> > :        type option being used.
> > :
> > : -march=cpu type
> > :        Generate instructions for the machine type CPU TYPE.  The choic-
> > :        es for CPU TYPE are: i386, i486, pentium, and pentiumpro.  Spec-
> > :        ifying -march=cpu type implies -mcpu=cpu type.
> >
> > Please also see the commit log for bsd.cpu.mk,v 1.13.
>
> Also see gcc.info, since the above seems to be from gcc.1 which is as out
> of date as a pentiumpro.
>
> bsd.cpu.mk should rarely be edited, but /etc.make.conf is per-machine so
> you can put anything you want in it.  However, defaulting to
> -mcpu=pentiumpro is just a bug, so I edit it out of bsd.cpu.mk.  It
> just micro-pessimizes for all CPUs that aren't pentium pros.  This is
> almost harmless for i386's because no one uses them, and almost harmless
> for P3's and maybe P4's because they share some bottlenecks with
> pentiumpros, but Athlons handle naive i386 code better than pentiums so
> many of the pentiumpro optimizations are pessimizations for athlons.

The choice if ppro was Peter's suggestion.  Feel free to offer a better 
default CPU to tune for.

> Note that CPUTYPE has worse bugs for i386's.  Setting it to a supported
> CPU gives -march instead of -mcpu, so using it gives unportable binaries,
> and bsd.cpu.mk provides no way to get the corresponding -mcpu settings.
> OTOH, CPUTYPE for alphas gives only -mcpu.

That is by design.  Note that on all non-i386 architectures such as alpha, 
etc. -mcpu means the same thing as -march.  The other architectures use 
-mtune to get the same effect as -mcpu on i386.

-- 
John Baldwin <jhb_at_FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org