GCC 3.2.1 Optimizations and Via C3 Ezra CPU

Joel Miller cheeziologist at mail.isc.rit.edu
Sat Feb 14 19:29:51 PST 2004


On Sat, 14 Feb 2004 21:04:36 -0600, Bryan K. Walton <zxcvbnm at tds.net> 
wrote:

> Hi,
> 	I have a question regarding compiler optimizations for the Via
> C3 Ezra processor. I did a little searching around on the web and found
> this:
>
> CHOST="i586-pc-linux-gnu"
> CFLAGS="-march=i586 -m3dnow -O3 -pipe -fomit-frame-pointer"
> CXXFLAGS="-march=i586 -m3dnow -O3 -pipe -fomit-frame-pointer"
>
> Now, that makes sense to me.  However, when I issue a "uname -m" on
> this box, it reports that it is a i686.  And sure enough, when I
> compile gcc on this box, without any optimizations, it seems to be
> identifying the host as i686-pc-linux-gnu.  Any ideas what might be
> going on here.  Is gcc incorrectly identifying hardware on the box?
> I'm using GCC 3.2.1.  Or can I specify i686 in those three
> optimization lines?
>
> Thanks!!
> Bryan Walton

IIRC the C3 processor is a 686 processor but it lacks the CMov instruction 
that other 686 processors have. Thus default i686 instructions will call 
CMOV and you will get an error stating an illegal instruction has been 
called. I also seem to remember hearing that newer C3's didnt have this 
problem. Take what I say with a grain of salt, as I'm trying to recall all 
this from memory.

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