I Want to Run 32-Bit Gentoo on AMD64 [Solved]

Message

palsyboy · Post by **palsyboy** » Wed Jun 18, 2008 11:51 pm

I'm upgrading from an Athlon XP 2000+ to a 2.5 GHz Athlon X2. My new motherboard only supports 2 GB of RAM, which is more than enough for my uses and takes out any need for the kernel to address more memory. For the sake of simplicity and because I have little to gain from 64-bit binaries other than unnecessary hassle, I'd prefer to just keep running a pure 32-bit system. However, will my new CPU be able to boot off my existing system, which was compiled for K7 architecture, not K8? If so, then I'm imagining I can just rebuild my kernel, change a few flags in make.conf, and rebuild everything from within a working system instead of having to do an installation from scratch. Is this correct? Pardon my ignorance, but this is my first 64-bit processor, and I'm hardly a Gentoo guru.

ShinyThings · Post by **ShinyThings** » Thu Jun 19, 2008 12:22 am

Should work. If more than just the processor will change though, you may want to rebuild your kernel with the appropriate drivers before upgrading. Otherwise, you may have to boot from a liveCD/USB/etc to do it.

zyko · Post by **zyko** » Thu Jun 19, 2008 12:27 am

However, will my new CPU be able to boot off my existing system, which was compiled for K7 architecture, not K8?

It might be able to boot. I suggest you prepare a liveCD just in case (everybody loves systemrescueCD). If your system doesn't boot, you can just fire up the liveCD, set your make.conf to use -march=k8, reconfigure your kernel to optimize for your new CPU and finally recompile your stuff.

/edit: sorry for basically duplicating Shinythings' reply -- it wasn't there when I started writing. I always dilly dally too long

Cyker · Post by **Cyker** » Thu Jun 19, 2008 5:33 am

It'll work; I went through the same upgrade path

But before you swap over the hardware, definitely re-compile the kernel with the right drivers, esp. network and sata/ide drivers!
It makes things much easier

The only other stuff you *have* to re-compile is hardware specific stuff, e.g. lm_sensors, as a K8 and run all K7 and older code with no issues at all.

acarstoiu · Post by **acarstoiu** » Thu Jun 19, 2008 2:27 pm

I find myself in the same hypothetical situation.
For things to start working, namely the computer to boot, the kernel to start, possibly complaining about a few modules (not vital ones!), is it really necessary to touch the kernel configuration? Will not any K7-code run unmodified on a K8?

I suppose that later on, one can recompile the whole system for K8 with -march=k8, but does that turn it automatically into a 64-bit system? I hope not. What is needed later on to gracefully switch to a 64-bit system?

Thanks.

zyko · Post by **zyko** » Thu Jun 19, 2008 4:13 pm

I suppose that latter on, one can recompile the whole system for K8 with -march=k8, but does that turn it automatically into a 64-bit system?

Nope. It'll stay i686 or whatever your CHOST indicates. (Note that you can't change your CHOST within a running system... well, you can, but it wouldn't work

)

I suppose that latter on, one can recompile the whole system for K8 with -march=k8, but does that turn it automatically into a 64-bit system?

That isn't really possible, at least not gracefully. You would need a new installation with an amd64-tarball.

palsyboy · Post by **palsyboy** » Thu Jun 19, 2008 4:43 pm

Thanks for the help, everyone.

It look as though I just need to compile support for K8 and the new northbridge, southbridge, and ethernet chipsets on the motherboard (thanks for the reminder, as I'd forgotten about those last three things). Everything else with the system will be the same. After everything is working, I'll still recompile everything for K8, or else I'll be driven nuts by my OCD. By the way, what's the easiest way to do this? I think it's "emerge -e system && emerge -e world" but want to be sure before I break something.

No matter what, though, I'll definitely have a LiveCD on-hand in case something goes wrong.

I suppose that latter on, one can recompile the whole system for K8 with -march=k8, but does that turn it automatically into a 64-bit system?

According to the AMD64 FAQ, a completely new installation is necessary. That, and worrying about the 32-bit chroot, are the reasons I decided to just stick with 32-bit, since there's no reason to invest so much time for so little benefit.

Cyker · Post by **Cyker** » Thu Jun 19, 2008 5:22 pm

acarstoiu wrote:I find myself in the same hypothetical situation.
For things to start working, namely the computer to boot, the kernel to start, possibly complaining about a few modules (not vital ones!), is it really necessary to touch the kernel configuration? Will not any K7-code run unmodified on a K8?

I suppose that latter on, one can recompile the whole system for K8 with -march=k8, but does that turn it automatically into a 64-bit system? I hope not. What is needed later on to gracefully switch to a 64-bit system?

Thanks.

All K7 code will run on a K8 unmodified.

As for the kernel, if the new system and the old system had *exactly* the same supporting hardware, then you would not need to recompile the kernel! :)

In practice, this is rarely the case, so you usually need different kernel modules for things like the disk controllers, network cards, system bus extensions, graphics etc.

Don'tworry about -march ; It doesn't determine whether your system is 32-bit or 64-bit, that's the job of the CHOST var in make.conf, but as others have said there is no clean way to move from 32-bit to 64-bit, anymore than there is to move from x86 to Sparc or PPC! :)

zyko · Post by **zyko** » Thu Jun 19, 2008 9:53 pm

By the way, what's the easiest way to do this? I think it's "emerge -e system && emerge -e world" but want to be sure before I break something.

I'm pretty sure emerge -e world is sufficient. This will emerge everything in system as well, because system is regarded to be a dependency of world. emerge -e system && emerge -e world will basically emerge system twice, wasting your precious time.

palsyboy · Post by **palsyboy** » Fri Jun 20, 2008 5:59 am

Thanks, zyko. CPU time is precious for the sake of foldingathome.

I just recompiled my kernel, though, and as I was about to copy arch/i386, I hit Tab and saw a new ia64 entry. I thought that must be where the new kernel was placed but then saw that /usr/src/linux/arch/ia64/boot didn't exist. Is this a problem? I'm guessing the new kernel image resides in /usr/src/linux/arch/i386/boot, but I want to make sure before I change out parts and then can't boot.

zyko · Post by **zyko** » Fri Jun 20, 2008 6:52 am

Look at the last couple of lines after you finished compiling your kernel. It normally tells you where your kernel resides. I would expect it to be in /usr/src/linux/arch/x86/boot.

IA64 is a completely different architecture, by the way (see wikipedia).

palsyboy · Post by **palsyboy** » Sat Jun 21, 2008 4:02 pm

Thanks. I have no idea why ia64 showed up.

Either way, I'm writing from my fully functional new system with all the apps recompiled. Thanks again for all the help.

zyko · Post by **zyko** » Sat Jun 21, 2008 10:02 pm

I have no idea why ia64 showed up.

/usr/src/linux/arch by default contains a folder for every architecture the sources can be compiled for, from alpha to xtensa, but both i686 and amd64 (the two most commonly used today) are referred to by their overall category, "x86".

After you enter "make", it tells you the path to your new kernel. But if you follow the gentoo handbook and enter "make && make modules_install", the output from the module's compilitation may scroll that line out of the user's sight

Congrats on your new system!