Smartest way to migrate a system from PII to VIA C3?[SOLVED]

Stever · Last edited by Stever on Tue Nov 20, 2007 5:02 pm; edited 1 time in total

OK, I'm sure some of these questions will become obvious once I get the hardware in hand, but I'm trying to do as much as I can in advance to make a smooth transition. This box is a pig when it comes to compiling, so I'm trying to get it right the first time.

I have a hardened gentoo router installation running OpenVPN, dnsmasq, shorewall, and not much else. It has been running on a PII 300 for quite a while, but now I'm about to get my hands on a VIA C3 Samuel MB, which should be an upgrade performance wise (especially for OpenVPN). I thought it would be quite painless to swap motherboards until I saw in the Safe CFLAGS wiki that this particular C3 needs i586 CHOST

I've looked through both the official and wiki CHOST change guides, and it all looks like it is geared towards an upgrade rather than a downgrade, and they don't inspire much confidence that it will work in any case.

So my questions to anyone with experience in this area are:
1) Do I really need to change CHOST or would changing CFLAGS be sufficient? Probably a silly idea, but one can hope

2) Is it reasonably likely that I can pull off a change of CHOST from i686 to i586?
3) Should I just throw in a new HD and start from scratch? This would have the advantage of a quick recovery if I make a mess of things

3a) If I start fresh, should I start with the x68 stage 3 tarball, or would that leave me right back where I started, needing to change CHOST?

Keruskerfuerst · Posted: Wed Nov 14, 2007 9:08 am Post subject:

1. Actual CHOST variable?
2. Before you replace the mainboard, CPU you should recompile the whole system (CFLAGS, CHOST).
3. Changing the CFLAGS and CHOST may result in a broken system.
3a. stage3 x86: yes; you should check the preset make.conf.

desultory · Bodhisattva Joined: 04 Nov 2005 Posts: 9410

neysx · Retired Dev Joined: 27 Jan 2003 Posts: 795

Stever · Posted: Wed Nov 14, 2007 5:05 pm Post subject:

Wow, thanks for all the responses. I think I have a better handle now on what to try:

1) Leave existing CHOST at i686 and rebuild existing system (kernel and all packages) with CFLAGS compatible with both PII and C3. This only takes 5 minutes of MY time, seems to have minimal chance of breaking the existing system, and neysx has given me hope that it will work in the new.
2) Install new MB, if it works then buy neysx a virtual beer

3) If not, it seems like a new install with x86 tarball is the way to go - then I can decide if it is worth the trouble of changing CHOST from 486 to 586 (my guess is probably not).

By the way, I like the C3 cluster - what do you use that for?

Stever · Posted: Thu Nov 15, 2007 5:50 am Post subject:

Hmmm, rebuilding the system (still on the PII) with CFLAGS="-O2 -march=pentium-mmx -pipe", but in a very bored moment I notice that the ebuild for glibc has decided it is smarter than me:

neysx · Retired Dev Joined: 27 Jan 2003 Posts: 795

Stever · Posted: Thu Nov 15, 2007 9:19 pm Post subject:

Stever · Posted: Sat Nov 17, 2007 4:31 am Post subject:

Well, finally got the new MB installed, but no luck. With the old PII, I had changed to CFLAGS="-O2 -mtune=pentium -pipe", then did emerge -e system, followed by emerge -e world, followed by rebuilding kernel with CONFIG_M586. Now with the new C3 MB, grub doesn't even load (did I need to reinstall it?), and if I boot with livecd I can't chroot into the old HD without getting "Illegal instruction".

At this point it seems the easiest path forward is to do a clean install, but I'm still curious whether I did something wrong, or if it is just not happy about the i686 CHOST. I guess I have the whole weekend to try and find out before I need this box back up and running

Stever · Posted: Sun Nov 18, 2007 3:33 am Post subject:

Still no luck. Did clean install with stage3-x86-hardened-2.6-2007.0.tar.bz2, then changed CHOST to i686 following Changing the CHOST variable, with CFLAGS="-march=c3 -O2 -pipe -fomit-frame-pointer -fforce-addr". Binutils builds OK, but gcc fail miserably with

loki_val · Posted: Sun Nov 18, 2007 7:48 am Post subject:

The C3 lacks the cmov instruction, which isn't technically part of the 686 specification, though every other 686 processor has it. It needs chost to be 586, otherwise it will bomb.

Stever · Posted: Tue Nov 20, 2007 5:00 pm Post subject:

neysx · Retired Dev Joined: 27 Jan 2003 Posts: 795

loki_val · Posted: Wed Nov 21, 2007 10:05 pm Post subject:

neysx · Retired Dev Joined: 27 Jan 2003 Posts: 795

Stever · Posted: Sat Nov 24, 2007 6:05 am Post subject:

I think he is referring to i386 in reference to this bug, which seems to be at least one of the reasons glibc is clobbering the -march.

And no worries about wasting my time - it is only wasted if I didn't learn anything, and at this point I think I have learned a bunch.

Now a potentially stupid question - what would break if I set CHOST="c3-pc-linux-gnu" ?