gcc compiler cputype, prescott or nocona confusion

[Jorn Argelo]

On Wed, 31 Jan 2007 23:40:38 +1100, Scott Killen <salkillen at internode.on.net> wrote:
> Hi,
> 
> When recompiling the world or kernel in FreeBSD i386 Rel 6.1 with,
> 
> "# make buildworld"
> or
> "# make buildkernel KERNCONF=MYSMPCONF"
> 
> (or building anything anything else for that matter), even though I have
> "CPUTYPE?=nocona" set in my "/etc/make.conf" file the compiler seems to
> head
> back to a default of  "-march=prescott" when compiling many of the
> functions
> on a Dual Xeon 3.6g (nocona) machine!
> 
> This doesn't happen when compiling for other machine types, I've tried it
> on a
> Dual PentiumPro, Dual PII, Dual PIII setting the CPUTYPE to the correct
> cpu
> type and the -march sticks to the assigned cpu type through all operations
> and produces nice quick optimized code.
> 
> Why is this so?
> 
> Is it because the "nocona" machine type optimization refers to the EMT64
> technology and thus is rejected when compiling for i386 targets rather
> than
> amd64 or emt64 targets and Gcc rejects it?

That's right. AFAIK the Nocona core is a prescott with EM64T support (feel free to correct me if I am wrong). Basically you have an i386 version of FreeBSD, and with EM64T instructions enabled GCC will build a 64-bit version of FreeBSD. I think that's the reason it switches back to prescott.

Jorn

> 
> Regards
> Scott K
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