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#1 2013-03-06 02:08:23

1Samildanach
Member
Registered: 2012-06-18
Posts: 11

[Resolved] Installed 64bit kernel with 32bit userland... *too* easy?

This is something I'd been thinking of doing for a while*, but I finally took a stab at it today. I opted for using a kernel from repo-ck, as that seemed the simplest option and has no real downsides (it even -theoretically- nets me improved performance). I commented out the "Architecture" line in my pacman.conf and manually set all repos (except ck, which I set to x86_64) to i686. After installing the new kernel and nvidia packages I updated grub and rebooted.

I ran uname -m to check everything was going to plan before I moved onto making things transparent... and got i686. So I tried "linux64 uname -m" and got x86_64. Which leaves  me wondering whether I've done something wrong (messed with some config file that I've forgotten about?) or a developer has done something clever (Allan, perhaps, since he was/is using a similar setup).

*Mostly so I could do 64bit Xen to allow me to do a 64bit Windows VM when I eventually get around to experimenting with VGA passthrough, since I've been happy enough with PAE.


In short: Should one be able to just drop in a 64bit ck kernel and have it work out of the box, or should I be fearing an imminent implosion?

Last edited by 1Samildanach (2013-07-01 05:09:30)

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#2 2013-03-06 02:17:17

WonderWoofy
Member
From: Los Gatos, CA
Registered: 2012-05-19
Posts: 8,412

Re: [Resolved] Installed 64bit kernel with 32bit userland... *too* easy?

I run the same ck kernel, and when I do "linux64 uname -m" I get x86_64 (as expected), and when I run "linux32 uname -m" I get i686 (also as expected).  I see no real reason why a 64bit kernel would happily run an i686 setup.  Off the top of my head, I know that Parted Magic does exactly this.

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#3 2013-03-06 02:27:10

1Samildanach
Member
Registered: 2012-06-18
Posts: 11

Re: [Resolved] Installed 64bit kernel with 32bit userland... *too* easy?

It's just that I was expecting to be doing this before uname -m would spit out i686. The blob post is a few years old, so it's entirely possible things have changed, but kernels are important enough that I want to be sure the issue is simply out of date information, rather than assuming everything is fine and later discovering that things have been busily screwing themselves up tongue.

Last edited by 1Samildanach (2013-03-06 02:27:59)

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#4 2013-06-30 17:14:28

brebs
Member
Registered: 2007-04-03
Posts: 3,439

Re: [Resolved] Installed 64bit kernel with 32bit userland... *too* easy?

1Samildanach wrote:

uname -m ... and got i686

Then you're *not* booting into a 64-bit kernel. Or are already using linux32 to fool it.

Crosstool filled in the missing link, for me to be able to compile a 64-bit kernel in a 32-bit system.

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#5 2013-06-30 18:40:48

kokoko3k
Member
Registered: 2008-11-14
Posts: 1,491

Re: [Resolved] Installed 64bit kernel with 32bit userland... *too* easy?

WonderWoofy wrote:

I see no real reason why a 64bit kernel would happily run an i686 setup.

Did you miss a "not" betweek "would" and "happily", or care to explain why?

I also wonder, apart from the OP specific case, if there are other advantages in running 32bit userland with a 64bit linux.

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#6 2013-06-30 19:47:30

WonderWoofy
Member
From: Los Gatos, CA
Registered: 2012-05-19
Posts: 8,412

Re: [Resolved] Installed 64bit kernel with 32bit userland... *too* easy?

Indeed there is a missing word there.  Sorry for the confusion kokoko3k

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#7 2013-07-01 05:38:54

1Samildanach
Member
Registered: 2012-06-18
Posts: 11

Re: [Resolved] Installed 64bit kernel with 32bit userland... *too* easy?

My memory is a little fuzzy, since quite some time has passed, but I recall it mysteriously working itself out at some point and bash is now set up the way I was expecting to need. I still have no idea what was going on.


While I'm at it, I may as well provide an update on the cause of the change: I ended up going with KVM instead of Xen, mostly due to the comparative simplicity. Using libvirt I was able get everything running, including 64bit Windows 7, though I found myself subject to the 2GiB RAM limit of 32bit libvirt (or QEMU? I can't quite remember which, and it may be both). I was going to mess around with a chroot and see if I could hack my way through the problem that way, but I got distracted by life and haven't gotten around to working on it again.

However, the most important thing is that I did it before it got popular tongue.

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