Mike Frysinger wrote:
> 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

What exactly doesn't make sense to you:
* building the toolchain in general:
   The application is quality assured to one specific gcc version, and
   I cannot expect that exactly this one version is available on the
   target machine, especially when some specific patches are required,
   or there is no gcc available at all, or the installation is just broken.
   And sometimes I do have multiple application releases on the same
   machine, requiring different gcc versions...
* using the 32bit host triplet:
   see below
* or disabling multilib:
   whenever possible I'd like to avoid messing with multilib.

>> 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.

Agreed. Although it is uncommon that Linux causes more headaches than Unix,
especially when it is about GNU packages.

>> 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.

> 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.

It is more an administrative thing: On Unix as well as x86-linux I simply
get 32bits from gcc. But for x86_64-linux I'm in need of an exception to
build/use some x86_64-gcc and wrap it with -m32, because I don't want to
force the application-maintainers to add this exception to add CFLAGS=-m32,
which can be interpreted as "require some change to keep it unchanged".
And it is ways easier to use --{build,host} than to create wrappers.

>> 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.

Well, "compatible" here means to me that when I do
$ configure --{build,host}=i686-pc-linux-gnu
on x86-linux, I'd like to expect this working on x86_64-linux too, as the
"_64" can be seen as an "extension"[1] to x86 I just do not want to use.

It turns out that it is the "/lib resolving to 64bit" thing only that
causes me headaches here, which actually is distro-specific.

[1] http://en.wikipedia.org/wiki/X86-64

/haubi/