Clarification needed on Handbook: Tracking for Multiple Machines

D J Hawkey Jr hawkeyd at
Sun Feb 22 07:07:25 PST 2004

On Feb 23, at 01:05 AM, Tony Frank wrote:
> On Sat, Feb 21, 2004 at 11:23:28AM -0600, D J Hawkey Jr wrote:
> > On Feb 21, at 05:56 PM, Gabriel Ambuehl wrote:
> > > 
> > > DJHJ> Second, two machines are of the same architecture, but they have different
> > > DJHJ> CPUs: One is an Intel PIII, but the other is a PII. Will the world built
> > > DJHJ> on a PIII be correct for a PII? Similarly, will the kernel for the PII
> > > DJHJ> built on a PIII be correct for the PII, given the different variables and
> > > DJHJ> settings in the two kernel configuration files?
> > > 
> > > Just make sure you build for 686. If that doesn't work, make it 586 (I
> > > think the PI qualifies as 686 but I'm not entirely sure). I think the extensions such as
> > > SSE etc are detected dynamically and shouldn't cause any problem.
> > > In all my years of messing with builds, I never run into this problem,
> > > so I guess it's pretty safe.
> > Yes, both [my] machines define I686_CPU.
> > 
> > "Dynamically", as in "at runtime"? I think you're right, but I don't
> > know for certain, either. This is exactly what I'm wondering about;
> > the PII has only MMX, for instance, while the PIII has SSE and MMX2.
> > 
> > I assume the world's codebase is CPU-agnostic within an architecture,
> > but I really don't want to assume this; I'd rather know this.
> I have PII, Celeron, PIII and P4 in my environment.
> All these use "I686_CPU" in my kernel configs (I got rid of the other I[345]_CPU types.

In a desktop's kernel config:
    machine         i386
    cpu             I686_CPU
    ident           SHEOL

In my laptop's kernel config:
    machine         i386
    cpu             I686_CPU
    ident           CHARON

Getting difficult, isn't it?  ;-,

Boot messages on that desktop from kernel built on that desktop:
    CPU: Pentium III/Pentium III Xeon/Celeron (764.35-MHz 686-class CPU)
      Origin = "GenuineIntel"  Id = 0x686  Stepping = 6

Boot messages on that laptop from kernel built on that laptop:
    CPU: Pentium II/Pentium II Xeon/Celeron (233.87-MHz 686-class CPU)
      Origin = "GenuineIntel"  Id = 0x652  Stepping = 2

> In /etc/make.conf I include "CPUTYPE=p2" as the lowest common denominator if 
> including a CPUTYPE flag.
> The resulting world & kernel run fine on all the systems.
> The higher flags p3 and p4 still just use -march=pentiumpro, however for SSE you
> will need p3 or p4 as MACHINE_CPU does not include SSE for p2 level.
> Check out /usr/share/mk/ for specifics.

If I read things right, the first chunk in results in
"CPUTYPE = i686"; the conditional-on-CPU_TYPE-defined assignment
sees "cpu I686_CPU" in the kernel configs, right?. The second
chunk in also results in "CPUTYPE = i686" (fallthrough).
The third chunk results in "_CPUCFLAGS = -march=pentiumpro", as
you state. Finally, the last chunk in results in
"MACHINE_CPU = i686 i586 i486 i386".

If I specify "CPUTYPE=p2" in make.conf, and I'm still reading
things right, the final result in would be the same
_CPUCFLAGS, and "MACHINE_CPU = i686 mmx i586 i486 i386".

But based on the boot messages, it would seem that the features of
the chips are detected correctly without specifying a CPUTYPE in
make.conf. So... As things are right now (no CPUTYPE in make.conf),
it would appear that "CPU feature" code is built into the kernels
on the respective machines, and that code correctly detects the
features available. Therefore, I don't see where adding CPUTYPE
in make.conf would get me anything I'm not already getting?

That is, why make things more specific than they have to be?
I don't see where adding "CPUTYPE=p2" on a PIII build machine
would change anything for PII and/or PIII target machines. What
have I missed?

> > > DJHJ> /etc/defaults/make.conf doesn't mention KERNCONF; /usr/src/Makefile.inc1
> > > DJHJ> does. Since /usr/share/mk/ sucks in /etc/make.conf, that should
> > > DJHJ> propogate KERNCONF to /usr/src/Makefile, right?
> To your original question, yes.
> Just add a KERNCONF= line to /etc/make.conf.
> First entry should be the local machine kernel (to install) and
> any subsequent entries will also be built during 'make buildkernel'
> make buildkernel builds all four.
> make installkernel installs MARVIN.

Cool. So, the -CURRENT (or is that -STABLE?) Handbook does apply
to 4.5-REL, at least where this stuff is concerned.


  ______________________                         ______________________
  \__________________   \    D. J. HAWKEY JR.   /   __________________/
     \________________/\     hawkeyd at    /\________________/

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