linux-kernel - Re: Multi kernel tree support on the same distro?

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Date:	Sun, 7 Jan 2007 10:30:57 +0100
From:	Willy Tarreau <w@....eu>
To:	Steve Brueggeman <xioborg@...si.com>
Cc:	Auke Kok <sofar@...-projects.org>, Akula2 <akula2.shark@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Multi kernel tree support on the same distro?

On Thu, Jan 04, 2007 at 10:28:12PM -0600, Steve Brueggeman wrote:
> There are some difficulties with gcc versions between linux-2.4 and linux-2.6,
> but I do not recall all of the details off of the top of my head.  If I recall
> correctly, one of the issues is, linux-2.4 ?prefers? gcc-2.96, while newer
> linux-2.6 support/prefer gcc-3.? or greater.

2.4 was designed for gcc 2.95.3 and supports gcc up to 3.4 on all platforms,
and up to 4.1 on x86, x86_64, ppc and sparc64. Recent gcc 3.4 produces good
code on 2.4, and is able to efficiently optimize for size (-Os) without too
much speed compromise.

> At any rate, what I've done is create a chroot environment.  I created this
> chroot directory by installing an older distribution that was created with
> linux-2.4 in mind (example, RedHat v8.2) into that at chroot directory.  The
> easiest way to do this that I'm aware of is to install the older distribution
> (minimal development, no server junk, no X junk) on another computer, then copy
> from that computer to a directory on your development computer.

Hmm, I think you did it the *hard* way. Gcc has been supporting
multi-version for years. You just have to compile it with --suffix=-3.4
or --suffix=4.1 to have a whole collection of gcc versions on your host.
If you don't want to recompile gcc, simply rename the binaries and you're
OK. When you build, you only have to do :

  $ make bzImage modules CC=gcc-3.4

I've been using it like this for years without problem. It's really
convenient, and it also allows you to easily compare output codes and
sizes between compilers.

Regards,
Willy

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