Re: [gentoo-dev] Re: crossdev and multilib interference

[Alexandre Rostovtsev <tetromino@gentoo.org>]

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On Wed, 2014-03-26 at 22:41 -0400, Mike Frysinger wrote:
> On Wed 26 Mar 2014 12:23:53 Ian Stakenvicius wrote:
> > On 26/03/14 12:12 PM, Mike Frysinger wrote:
> > > that's bs.  people install crossdev to get a cross-compile
> > > environment, not to get something that only works through `emerge`.
> > > attempting to restrict it so it only works through `emerge` is
> > > unacceptable and it has never been that way.
> > 
> > it -does- make sense though to limit anything that one wants to EMERGE
> > with the crossdev, to require the use of cross-emerge.  Would it not
> > be possible to somehow ensure the crossdev tools are ignored
> > in/removed from/cannot pollute the standard emerge environment?  Are
> > there any use cases where one -would- want the crossdev to be used in
> > a standard emerge environment instead of using cross-emerge ?
> 
> you've lost me.  when you `emerge-$CTARGET`, that package doesn't go anywhere 
> near your ROOT=/ system.  it's entirely contained in /usr/$CTARGET/.
> 
> when you run `crossdev $CTARGET`, it installs all the standard $CTARGET-xxx 
> tools in /usr/bin.  this isn't "polluting" the environment at all ... in fact, 
> they're living right alongside existing tools.
> 
> as i pointed out elsewhere in this thread, the problem is that multilib relies 
> on automatic detection of the toolchain *failing* so that it falls back to the 
> native value.  in other words, when you run `./configure --host=i686-pc-linux-
> gnu`, it tries to find e.g. i686-pc-linux-gnu-ar.  it doesn't exist so the 
> fallback is used (plain `ar`).  multilib is using these tuples so that the 
> standard checks (autoconf/eclasses/etc...) trigger in the right ways for the 
> cpu/os/userland combinations.
> 
> since crossdev installs a full proper toolchain for the target, the one 
> multilib was using to lie now exists and its toolchain is used instead.
> -mike

Crossdev is "polluting the environment" in the specific case that we are
talking about - secondary native ABIs on a multilib system.

An amd64 multilib system is not expected to build MIPS binaries that
would be hosted on itself. So of course anyone using amd64 undersands
that mips-pc-linux-gnu-ar is part of a cross-compile toolchain, no
matter whether it's in /usr/bin or /usr/libexec/crossdev or anywhere in
the filesystem.

However, an i686 crossdev on an amd64 multilib system is a fundamentally
different situation. An amd64 multilib system *is* expected to build x86
binaries that would be hosted on itself. So i686-pc-linux-gnu-ar is
expected to be not a part of any cross-compile toolchain, but a part of
the native toolchain for the machine's secondary native ABI. Especially
when i686-pc-linux-gnu-ar is in /usr/bin.

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