Kernel config for 32-bit Gentoo on Athlon64 [solved]

geoffp · n00b Joined: 10 Oct 2004 Posts: 47

Hey, all --

If I'm running a 32-bit x86 install on an Athlon 64 or Sempron (64), is it safe to select "Athlon64/Opteron/Whathaveyou" under "Processor Type and Features" when configuring my kernel? Will that generate a 64-bit kernel, or a 32 bit one?

I've read in many a wiki that you can sure pass march=athlon64 to GCC, and it will generate 32-bit code (as long as your CHOST is "i686-pc-linux-gnu" or similar), so by extension, I'm wondering if that's all that kernel config option does. Or will it build with a different CHOST as well...?

I bet I'm not the only one wondering this.

Thanks in advance if you have any insight.

wizard69 · Apprentice Joined: 22 Sep 2003 Posts: 178 Location: Berlin

That should get you going check out the wiki. These are safe cflag settings http://gentoo-wiki.com/Safe_Cflags

Sempron/Sempron64 (AMD)

* If it is a Socket A (Socket 462) Sempron you can be sure it is neither 64-bit capable nor SSE2/SSE3 capable.
* If it is a Socket AM2 Sempron you can be sure it is both 64-bit and SSE3 capable.
* If it is a Socket 754 it depends on the stepping (part number):
o Steppings: CG (Part No.: *AX) or D0 (Part No.: *BA) have neither SSE3 nor AMD64
o Stepping: E3 (Part No.: *BO) has SSE3
o Stepping: E6 (Part No.: *BX) has SSE3 and AMD64
* Anyway you should check /proc/cpuinfo for pni (SSE3) string before using -msse3.

vendor_id : AuthenticAMD
cpu family : 15
model : 44
model name : AMD Sempron(tm) Processor

Note: The model number may differ.

32 bit (Socket A)

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=athlon-xp -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

32 bit

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=athlon64 -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

32 bit (SSE3 capable)

CHOST="i686-pc-linux-gnu"
CFLAGS="-march=athlon64 -msse3 -O2 -pipe -fomit-frame-pointer"
CXXFLAGS="${CFLAGS}"

Sempron64 - 64 bit

CHOST="x86_64-pc-linux-gnu"
CFLAGS="-march=athlon64 -msse3 -O2 -pipe"
CXXFLAGS="${CFLAGS}"

geoffp · n00b Joined: 10 Oct 2004 Posts: 47

Thanks for your effort, Wizard, but that's not really what I'm asking. The CFLAGS in my make.conf I've got a good handle on. It's the kernel config option that I'm curious about.

geoffp · n00b Joined: 10 Oct 2004 Posts: 47

So I worked up the nerve to try it, and it works! I've compiled the kernel with "Opteron/Athlon64/Hammer/K8" under "Processor type and features"->"Processor Family" and my system is still (apparently) humming along in 32-bit mode. Question answered!