Moving a Gentoo install from AMD64 to Intel Core 2 Duo

Dakeyras · n00b Joined: 31 May 2007 Posts: 17

Hello everyone,

I'll be upgrading my faithful Athlon64 3500+ to a Core 2 Duo CPU in about a month and I'm willing to keep my system bootable on both architecture while transitionning. First off, is this even feasible ? My current build settings are :

Sadako · Posted: Mon Jul 23, 2007 6:42 pm Post subject:

march=athlon64 will include 3dnow extensions, which aren't available on intel.

Unfortunately, there doesn't appear to be a simple "march=x86_64".

What you could try is either changing the march to something which only includes the extensions available on both cpus (nocona seems like a good bet, as your athlon64 seems to supports sse3/pni),
or adding "-mno-3dnow" to your cflags, however I really don't know if either will work right, and both would require rebuilding everything.

The problem with march=i686 is you'll completely lose the 64-bit extension support, so I don't think it'll be of any use to you.

The ~amd64 won't be an issue.

My advice?
Change your march to nocona, then (re)compile something and see if it runs or returns "illegal instruction".

mplayer would be perfect for this, however it is the only package I've come across that actually enables support for your cpu regardless of what you have in make.conf.
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Dakeyras · n00b Joined: 31 May 2007 Posts: 17

Thanks for the quick reply (I didn't even have the time to finish eating

).

Sadako · Posted: Mon Jul 23, 2007 9:52 pm Post subject:

With i686, you would basically be running a 32 bit system.

I'm really not sure what it would involve, there might be some way to make it work, but I think it'd be kinda messy, I'd say nocona has more potential.

Also, as nocona is probably what you'd be using after switching cpu, it makes a lot more sense if it works.

xchat has the mmx USE flag, so out of what you posted I think that would be a useful test, and I'd try vlc too.
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loftwyr · Posted: Tue Jul 24, 2007 12:36 am Post subject:

You can't compile march=i686, gcc wouldn't accept it on your arch. What you will need to do is rebuild your kernel with processor type set to generic x86-64 and then reboot with your new hardware. Once you've rebooted, set your march to nocona and

Sadako · Posted: Tue Jul 24, 2007 12:46 am Post subject:

Dakeyras · n00b Joined: 31 May 2007 Posts: 17

A quick update: I've made a few tests yesterday with '-march=nocona', re-emerging a few applications (audacious, vlc, pidgin) and it seemd to work OK. I've then launched an 'emerge -e world' during the night. I'm now at 543 of 669 packages built, and the system is rolling OK for now. Portage just rebuilt apache2 and PHP, I ran some tests on those two as well, it's going good.

I also had completely forgotten to check my USE flag: it has both '3dnow' and '3dnowext'. However, only two applications on my system use any of those, mplayer and mpg123, so I can probably continue for now and tweak those two later.

One quick question: I've only re-emerged world, will I also have to re-emerge system as well ? Even though it's recommended to do system before world, I hope going the other way around won't screw things up too badly.

Thanks again for the help.

Dakeyras · n00b Joined: 31 May 2007 Posts: 17

After emerging system with the new CFLAGS and rebuilding the kernel for a generic x86-64 architecture, all seems to be functionning smoothly. I'll probably bump this thread back if I encounter some malfunctions, or when I change my hardware.

Later.

Akkara · Posted: Thu Jul 26, 2007 1:19 pm Post subject:

norbee · n00b Joined: 24 May 2007 Posts: 3

Hello Dakeyras,

Did you changed the hardware? Was everything working for you as it should? I will do the same in few weeks...

Thanks.

n.

piwacet · Guru Joined: 30 Dec 2004 Posts: 486

Just one other thought on the kernel issue... you could compile a separate kernel with a .config appropriate for core2duo, and keep your current working kernel around, and if need be, you could use grub to select the core2duo kernel when you make the switch.

Maybe you won't need to do this as it sounds like you've made a generic 'x86_64' choice in your kernel config, but just thought.

Alakhai · Apprentice Joined: 16 Oct 2003 Posts: 151

Maybe the safest way should be to set

Belliash · Posted: Thu Sep 06, 2007 7:30 am Post subject:

Sadako · Posted: Thu Sep 06, 2007 3:26 pm Post subject:

Belliash · Posted: Thu Sep 13, 2007 5:24 pm Post subject:

BlackSash · Posted: Thu Jan 08, 2009 3:51 pm Post subject: Running into this now

My apologies for bumping this thread, but I have this same issue and I have an additional question:

I'm now in the process of recompiling my system for generic x86-64 (via the march CFLAG), however I'd like to know if my CHOST would need to change from x86_64-pc-linux-gnu or that I can keep it as is. I've been running the same hardware for 3 years and am bout to switch, so I haven't had to touch this for a long time.

Also there is the problem, that I have not seen mentioned anywhere, of profiles. Back in the day my system was installed from a 2007.0 amd64 installcd. This has set all my available profiles to amd64 variants (enabling the 3dnow flags, for one thing). How do I switch these profiles to either generic x86-64 (if they exist) or regular x86 otherwise.

For the continued health of my installation i think it would be prudent to get everything working nicely, and since I need to upgrade to 2008 anyway, i'd like to switch the profiles around to support my new system as well.

Any tip on this would be appreciated, and if any information is required, ask away.

loftwyr · Posted: Thu Jan 08, 2009 3:57 pm Post subject:

Just leave your CHOST as is, the X86_64 is the generic name for all 64bit processors.
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zyko · Posted: Thu Jan 08, 2009 10:25 pm Post subject:

Instead of recompiling everything twice, you could just boot the new hardware with a live-CD, chroot into your Gentoo and recompile it (once).

kabage · Guru Joined: 31 Jan 2005 Posts: 340

with a amd3400 to q6600 quad core. Compiled the kernel to include all the drivers for
my new mobo, especially ethernet. (of course what did nt work) ethernet
was the only problem ,

when i pulled my hd from old to new computer, udev still set up my old ethernet
making my new one eth1 instead of eth0. Of course it took me awhile to find that.

I never had a problem running anything. I guessing I had my march set to nocona,
since that is what is at the moment, I dont remember ever changing it on my new computer.
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minor_prophets · Apprentice Joined: 07 Oct 2007 Posts: 281

Also, someone correct me here if I'm wrong, but any system with gcc-4.3.x and up, the CFLAGS could(should?) be set to march=native to all gcc native detection of all your CPU features.

loftwyr · Posted: Mon Feb 23, 2009 10:55 pm Post subject:

-march=native selects the right options for your kernel at compile time. If you change hardware then it wil have issues.
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Have you run revdep-rebuild lately? It's in gentoolkit and it's worth a shot if things don't work well.
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