[gentoo-amd64] Re: Re: Giving up 64 platform

[Duncan]

Allan Spagnol Comar posted
<1cc2dc830604240812r599a7aefw652004ac34827092@××××××××××.com>, excerpted
below,  on Mon, 24 Apr 2006 12:12:08 -0300:

> Hi all, Thanks for all the advises !!!
>
> I will try run some binary 32 bits programs ( until now I was using
> just source programs )
>
> I got curious with chroot enviroments, is there any literature that I
> can find ( like manuals and samples, I am newbee speaking of cross or
> dual platforms ).

I thought it might be this thread I posted all the Gentoo URLs too.  It
wasn't.  However, you are in luck, because Gentoo is known for the quality
of its documentation, and Gentoo for AMD64 has a decent collection of its
own on our hardware, including one specifically on setting up chroots for
32-bit on a 64-bit platform.  =8^)  Listed below.

> Duncan, you real are a little radical but I like some of your
> thoughts, one thing that make me curious it will be about the
> advantages of using a gentoo x86 on a AMD64, once I would not be able
> to make optimizations on compilation flags ?

You have actually three choices, here, all sticking with Gentoo, only one
of which doesn't allow you to manage CFLAGS and the like in 32-bit mode.
=8^)

A basic rule of multilib is that trying to load a 32-bit library
in a 64-bit program cannot and will not work.  (The reverse is also true,
32-bit programs can't /normally/ load 64-bit shared objects into their
execution space.  Games are the major example here.) The problem is that
all these binary-only slaverywares, mostly codecs and browser plugins, are
available for Linux in 32-bit binary-blob-only shared objects (*.so, the
Linux equivalent of the MS platforms' DLLs). They are designed to be
loaded into 32-bit browsers and 32-bit media players.  They simply won't
work in the 64-bit equivalents.  

That's the problem.  As I said, there are three solutions available for it
within the Gentoo system.

Option One:

For those who don't run a lot of 32-bit stuff, and don't care so much
about 32-bit optimization, there's the default multilib setup that most of
us run.  Selected apps, among them firefox (covering the 32-bit browser
plugin problem) and mplayer (for the 32-bit codecs) are available
precompiled, as firefox-bin and mplayer-bin.  Likewise, the most
frequently needed 32-bit libraries are available in 32-bit binary
compatibility packages.  There's a list in one of the documents below, but
for games and etc. with ebuilds, the dependencies are taken care of by
portage as usual.  The list, therefore, is mostly in case you run the game
installers or compile your own 32-bit programs outside of portage.

That's the non-optimized choice -- you trade the ability to optimize for
the convenience of the pre-built binary packages.  Note that the
non-optimized qualifier only applies to the 32-bit compatibility stuff. 
The 64-bit side of your system is handled as usual in Gentoo, as you are
likely already aware since you've been running it and getting frustrated
with the 32-bit problems, since you didn't understand them. =8^(

Option Two:

The first optimized choice is the chroot option.  Again, your system is
64-bit in general, but you run a 32-bit chroot that's almost (but not
quite, you don't need 32-bit sysloggers or kernels for example as the
64-bit side provides those) an entire Gentoo x86 system on its own.  In
this chroot, you run a second version of portage, that doesn't know about
the 64-bit side, only its 32-bit stuff.  It tracks all your 32-bit
dependencies just like portage normally does for a system.  You configure
this chroot version of portage with all the usual optimization stuff,
CFLAGS and the like, you'd normally use on a 32-bit x86 system.  From
inside the chroot, the system looks just like a normal 32-bit system, only
missing the system service packages (like your syslogger) provided by the
64-bit side.  You want to run a 32-bit KDE installation?  Merge it. 
Gnome?  Merge that.  With a bit of remount trickery, you can expose the
same /tmp and /home partitions (and the portage tree if you have it on its
own partition) for both the 32-bit chroot and the 64-bit main system. 
This lets the 32-bit stuff see the X sockets and the like in /tmp, and
gives you access to the same /home dir and personal login settings  on
both sides.  The chroot of course has its own root, inside the main system
root, as that's how a chroot works.  /usr and /var likewise remain
separate.

Keep in mind, however, that the chroot is normally only needed for
compiling stuff -- it's where the 32-bit only aware version of portage
runs.  You then add the 32-bit bin paths and 32-bit LDPATHs to your main
system configuration, and when properly configured, you can then run
binaries from either the chroot or the 64-bit main system alike -- the
32-bit binaries can't load the 64-bit libraries anyway, and don't try. 
The 64-bit binaries likewise, only load the 64-bit shared objects.

What happens if you have both a 32-bit and a 64-bit firefox (for example)?
Which one does the system run?  Easy.  If you don't type in the path,
only typing "firefox", it runs the one located in the directory that
appears first in your path.  If you want 32-bit as the default, set it
first in your path.  64-bit?  Set that first.  To run the other one, you
simply use the full path, /usr/bin/firefox or whatever.

The chroot doc has more info, but the key thing to remember about chroot
is that it's most useful for those doing enough 32-bit stuff to make the
additional hassle of running and keeping uptodate almost an entire second
system worth the trouble.  You can compile by hand individual
32-bit packages using multilib, but portage can't handle the deps (except
for its binary compatibility packages, which are tracked separately from
the regular from-source versions) of both 32-bit and 64-bit at the same
time, so if you are compiling enough to make tracking the deps manually a
big headache, or if you want fully optimized 32-bit stuff and don't want
to do it manually, the chroot is the way to go.  More work to keep up both
the main system and the chroot, but you get both systems fully optimized
as you wish.

Option Three:

The third choice is the one that I was recommending you consider, in the
previous reply, based on the problems you mentioned.  If 64-bit is too
much hassle but you like Gentoo, simply stick with it, and put 32-bit
Gentoo on your system, instead of 64-bit.  You do lose a bit of
optimization possible in 64-bit mode, but the AMD64 platform makes a very
good 32-bit platform as well, and 32-bit stuff runs on it every bit as
fast (often faster, because AMD64 is very good even in 32-bit only mode)
as it would run on any other 32-bit system.

The idea here is that you pretend your AMD64 is a regular x86, forgetting
about 64-bit altogether (at least for now, you can always decide to try it
again in a year or two), and download a regular athlon/x86 stage and
install from that, instead of using the amd64 stages.  Your keywords are
x86 or ~x86, not amd64 or ~amd64.  You run a 32-bit gcc and a 32-bit
distribution in every sense of the word.  The hardware is still 64-bit,
but you are running a full 32-bit Linux system on it, no 64-bit software
at all.

The reason I think this fits your needs is because you said you liked
Gentoo for x86, and were just tired of all the hassles of Gentoo for
AMD64.  You were thinking about running another distribution, a binary
one.  That's definitely an option available, but it doesn't to me sound
like one you'll be happy with, because you like Gentoo, you just don't
like the AMD64 hassles.  So get rid of the amd64 hassles and just install
a 32-bit Gentoo on the system!  There's nothing saying you can't do that,
and in fact, AMD specifically designed AMD64s for that possibility.  Keep
in mind that in the MSWormOS world, most folks were running a standard
32-bit MSWormOS on their 64-bit system for quite awhile, because MS was
much slower in making a 64-bit OS available than Linux was!

This list deals with the AMD64 Gentoo, so if you went regular 32-bit only,
you'd probably find little of the discussion here of interest.  You'd use
the regular forums and user list, just as every other x86 Gentoo user
does.  Likewise, the docs I'm about to list apply to Gentoo for AMD64, not
Gentoo for x86, so if you choose this option, feel free to ignore them. 
Your installation will be x86 Gentoo in every sense of the term, just like
the other x86 Gentoo systems you've run in the past.

The docs list:

Here's a list of docs for Gentoo AMD64 that should help.  Of particular
interest will be the FAQ, which should provide a bit more help deciding
which of the above options is for you (tho I don't believe it deals with
the x86-only option), and the chroot guide, which will give you a much
better idea of how that works, and if you choose that option, guide you
thru setting it up.

Gentoo AMD64 FAQ
http://www.gentoo.org/doc/en/gentoo-amd64-faq.xml

32-bit chroot Guide for Gentoo/AMD64
http://www.gentoo.org/proj/en/base/amd64/howtos/index.xml?part=1&chap=2

Creating 32-bit Packages for Gentoo AMD64
(This is a user page, not an official Gentoo page.  It probably won't be
useful to you right now, but it's an interesting read, particularly if you
already have a chroot setup.)
http://www.andyjeffries.co.uk/32bit-ebuild-amd64.html

One of the devs created a script that automates part of the chroot stuff,
if you want to go that route.  I don't believe it's officially supported,
and Travis Tilley's dev page is no longer there (IIRC he moved on to
other pursuits and is no longer a Gentoo dev) but here's the links to it
and the docs, as mirrored.  Note that these are hosted by the same guy who
wrote the 32-bit packages doc, above:
Script:
http://www.andyjeffries.co.uk/32bit/setup-gentoo-chroot 
Docs:
http://www.andyjeffries.co.uk/32bit/chrootthingiehowto

The old, deprecated Technotes.
(This has been replaced by the FAQ, but it's still useful as a historical
reference, and because it covers most of the same stuff as the FAQ, but in
a different way.  Sometimes reading the same thing put two different ways
helps one understand it, so the technotes remain useful in that regard.)
http://www.gentoo.org/proj/en/base/amd64/technotes/index.xml

Hope all that helps, and may your choice be a pleasant one! =8^)

-- 
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 in
http://www.linuxdevcenter.com/pub/a/linux/2004/12/22/rms_interview.html


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