[gentoo-amd64] no-multilib and 32-bit chroot

[gentoo-amd64] no-multilib and 32-bit chroot

[Duncan]

Just in case anybody ever wondered, there's nothing stopping someone from 
doing the 32-bit chroot (as in the gentoo/amd64 documentation) on a
no-multilib system.  In fact, it's a cleaner way to do it, since the two 
systems will be fully separated, no 32-bit stuff on the 64-bit side, and 
no 64-bit stuff on the 32-bit side, plus no generic 32-bit binary-only 
emul-linux-x86 libs to worry about.

The one caveat is to make sure you have the kernel set to handle 32-bit 
also (in menuconfig, under executable file formats, ia32 emulation), but 
that's needed for grub-static anyway, I believe, so no big deal there.

I've been running no-multilib for quite some time and definitely prefer 
it on the 64-bit side.  But I've had a netbook (Acer Aspire One, from 
before they went with the freedomware crippled poulsbo chipset) that only 
does 32-bit, and I'm finally getting around to sticking Gentoo on it.  So 
I did the 32-bit chroot stuff to build the image for it as my main 
machine is far faster, tho I wasn't sure if it was going to require at 
least a 32-bit glibc and ld/linker (and thus multilib) on the main system 
or not.  I thought it /should/ be fine, tho, and was correct.  All it 
needs is the standard 32-bit chroot stuff.  Just setup the initial dir, 
unpack the 32-bit stage-3, and setup the mounts as outlined in the chroot 
guide, and the linux32 chroot /file/system /bin/bash command works as it 
should.

Since I'm doing it as a full system setup to be transferred to my netbook 
later, not just the usual chroot stuff, I had a bit more to do than the 
guide mentioned, and the x86 handbook installation section wasn't quite 
right for me either, tho I followed it relatively closely except that I 
haven't configured fstab or grub yet, and of course didn't partition the 
disk since that was already setup on my main machine.  I'll have to do 
that later, when load the image on a thumbdrive, boot the thumbdrive on 
the netbook, and then use it to setup partitioning, etc, on the netbook's 
drive (I got the 120 gig conventional magnetic platter SATA, not the SSD).

FWIW, I just got thru with an emerge --emptytree @system and am now doing 
an emerge --emptytree @selected for the few world packages I have, after 
updating @system to gcc 4.4.2 (~x86) just previous to emerging
--emptytree @system.  I still have to add most of world, including xorg, 
kde, icecat, etc.  I'm figuring I'll have a Christmas present for myself, 
tho. =:^)  That's including both finishing the build, and the final setup 
on the netbook too, I hope.

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman

Re: [gentoo-amd64] no-multilib and 32-bit chroot

[Jesús Guerrero]

On Sun, 20 Dec 2009 14:30:57 +0000 (UTC), Duncan <1i5t5.duncan@cox.net>
wrote:
> Just in case anybody ever wondered, there's nothing stopping someone
from 
> doing the 32-bit chroot (as in the gentoo/amd64 documentation) on a
> no-multilib system.  In fact, it's a cleaner way to do it, since the two

> systems will be fully separated, no 32-bit stuff on the 64-bit side, and

> no 64-bit stuff on the 32-bit side, plus no generic 32-bit binary-only 
> emul-linux-x86 libs to worry about.

It's all about options. I find it cleaner to pursue the true multilib (as
implemented in the multilib overlay) than to have to OSes just to run a few
apps. That feels like having a Windows installation just to run a couple of
games: hackish at best. But, as said, it's just a matter of opinions.
There's no absolute best option, it depends on your tastes. This way you
can get things like true DRM working no matter what kind of binary you are
using.
 
> The one caveat is to make sure you have the kernel set to handle 32-bit 
> also (in menuconfig, under executable file formats, ia32 emulation), but

> that's needed for grub-static anyway, I believe, so no big deal there.

However you don't need that for grub. You can install grub to your MBR
from a livecd and then forget about it. Unlike lilo, grub doesn't need to
be reinstalled each time you add a new kernel to your menu.

-- 
Jesús Guerrero

[gentoo-amd64] Re: no-multilib and 32-bit chroot

[Duncan]

Jesús Guerrero posted on Sun, 20 Dec 2009 20:49:46 +0100 as excerpted:

> It's all about options. I find it cleaner to pursue the true multilib
> (as implemented in the multilib overlay) than to have to OSes just to
> run a few apps. That feels like having a Windows installation just to
> run a couple of games: hackish at best. But, as said, it's just a matter
> of opinions. There's no absolute best option, it depends on your tastes.
> This way you can get things like true DRM working no matter what kind of
> binary you are using.

Absolutely!  I realized some time ago that because I don't do closed 
source and most common FLOSS has already been ported, the chance of me 
needing 32-bit multilib was essentially nill -- with the exception of 
grub/lilo since amd64 continues to boot in 16-bit legacy mode, for legacy 
reasons (as long as the pc/mbr disk format stays around, at least, I 
understand EFI/GPT can handle direct 64-bit booting, or at least the 32-
bit portion is EFI and it can load 64-bit directly), if I wanted to 
continue actually compiling them from source.

But what I'm doing here isn't exactly multilib, but much more literally, 
taking advantage of the bi-arch/bi-bitness nature of amd64, to assemble a
32-bit image for my netbook on my generally WAY more powerful dual-dual-
core amd64 machine.  I'll continue to do all the Gentoo updates to the 32-
bit chroot on my main machine, and will likely eventually rsync the atom 
to the 32-bit chroot image.  Of course, I don't have to worry about that 
immediately, and I'm not -- I'm simply building the image right now, I've 
not even figured out what my partition layout's going to be on the atom.  
Once I get most stuff installed, I'll copy everything to a USB drive, 
setup grub and a temporary fstab on it, and boot from it on on the 
netbook/atom.  Once that's working correctly, I'll gdisk the atom's 120 
gig hd, mkreiserfs or perhaps experiment with btrfs on it, then copy the 
image over on to it, make it bootable, and go from there.  Only after 
/that's/ all working, and decide what I'm going to do with networking as 
well, will I need to worry about updating, and since I use 
FEATURES=buildpkg, I can simply copy the binpkgs to USB stick and 
"sneakernet" them until it's convenient to setup rsync or some such.

Of course that's going way beyond multilib, since it's fully imaged multi-
arch (tho I don't plan on ever making the 32-bit image on my main machine 
actually bootable -- I'd have to stick an entirely different mdraid 
config in grub, then figure out the partition to point root= at, to do 
that, and since I already have a second fully bootable 64-bit 
installation snapshot as a backup, there's little point in making the 32-
bit actually bootable on the main machine), but that's what's great about 
Gentoo and the 32-bit chroot feature documentation and support -- it's so 
flexible in that regard! =:^)

So definitely, it's all about options, and how Gentoo makes so many more 
of them reasonably easily available, especially compared to the standard 
but relatively limited bindists.

-- 
Duncan - List replies preferred.   No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master."  Richard Stallman