Re: [gentoo-dev] RFC: multilib and the compatibility to singlelib

[Mike Frysinger]

On Tuesday 20 October 2009 09:06:29 Michael Haubenwallner wrote:
> As I'm building the toolchain myself too, I configure it with the
> 32bit host triplet on each platform, usually disabling multilib.

this doesnt make any sense to me

> This simply works for ppc-aix, hppa-hpux, ia64-hpux, sparc-solaris,
> x86-solaris, even if the underlying OS/kernel is 64bit.
> It isn't even necessary to explicitly use --{build,host} at all,
> as config.guess tells the 32bit triplet on these platforms.
> Additionally, even their default compiler output is 32bit.
>
> But Linux "is not Unix":

you're right, so i'm not terribly concerned with compatibility with non-Linux 
systems.  comparing the native Gentoo/Linux multilib setup to another Linux 
multilib setup is the only useful comparison.

> Configuring both binutils and gcc needs to be done with:
>   $ CC="gcc -m32" /path/to/configure --{build,host}=i686-pc-linux-gnu ...
> This works on 64bit RHEL as well as on 64bit SLES (both have 32bit in /lib,
> 64bit in /lib64, no /lib32), but breaks on amd64+multilib Gentoo Linux.
>
> Problem is that, as x86-linux isn't a multilib target, both ld and gcc
> search for 32bit libs&objects in /usr/lib:/lib, as they don't know about
> /usr/lib32:/lib32. The error when bootstrapping gcc is:
>   /usr/lib/crti.o: file not recognized: File format not recognized

i dont get it.  why does the i686-pc-linux-gnu toolchain target matter on an 
amd64 multilib system ?  the native x86_64-pc-linux-gnu toolchain should 
already do the right thing when given -m32.

> While it is possible to patch binutils[1] and gcc[2] to search in
> /usr/lib32:/lib32 even with this otherways non-multilib target,
> it doesn't feel like the "right thing" to enable multilib for
> just one multilib option.
>
> Isn't the intention of multilib to have a new (64bit) system
> be compatible with the corresponding old (32bit) system?

your description of "compatible" is pretty vague.  ignoring /lib -> /lib64 
symlink (which shouldnt matter to any binaries), i'm not aware of any 
differences off the top of my head.
-mike