Changing the CHOST variable/en

This document explains how to change the CHOST variable of an existing system.

Introduction
Changing the CHOST is a big issue that can seriously screw up your system - so why is there a guide for that it at all?

There are certain situations where changing the  variable is inevitable, e.g. when upgrading to glibc 2.4 which only supports nptl and the user finds out that the current   is i386, which makes it impossible to use nptl. In this case, there are not a lot of options, and changing  is one of them.

Even if following these instructions, problems may arise, so please make sure you read and execute them very carefully. In this example the CHOST will be changed from i386 to i686, if you do another change, please change the commands accordingly.

Building the packages
To start out with the CHOST change, edit the file and change CHOST value to suit your needs. Then, rebuild the following packages in this order:

Verifying things work
Now it is time to make sure that your  and   settings are sane and you do not have any leftovers in.

The output of  and   should look like this (may differ according to your gcc version and chost, gcc 4.1.1 and i686 here):

Next, check to see if there are references to the old CHOST in :

Before deleting the file, let's check for files with the updated CHOST:

This one looks good as there should always be only one file for  in  (05gcc in this example), so let's delete the one with the wrong references:

The same also applies to  - if there's an extra one, see which is the outdated one and delete it. Next, check your

That one looks good, those two files actually should be there. Time to move on to the gcc directory.

and are fine, but  is another leftover that needs removal.

Now run the following commands to update your environment:

Next, verify everything is fixed:

If you still find something, you must have missed some file, try to track it down before going on.

Finishing The Change
Now it is necessary to re-emerge  and run. Make sure to use the correct gcc version (your current one, 4.1.1 here) and pass your old architecture (i386 here) as argument. Replace $CHOST with your new CHOST, and  with your gcc version. This example assumes a CHOST of i686.

You may want to rebuild all your packages:

Now, in theory it should not be necessary to do so, but it can not be 100% guaranteed that this is actually the case. If you do not recompile the world target, I have been told at least some packages need recompiling, so you should do:

The following set of packages really need to be rebuilt:

All packages using perl install to the  directory and hence need rebuilding. In case qfile is not available on the system yet, install first.

Now rebuild all packages that have files installed in any location:

If you encounter other packages that need recompiling, please let the author of this document know.

Common problems
When upgrading from gcc 3.3 to 4.1 at the same time as changing the CHOST (please don't do that anyway), a couple of users reported broken packages that need recompiling, such as groff and courier:

This happens because during the upgrade, the CHOST doesn't exactly match CTARGET and the compiler assumes cross-compiling. As a consequence, LDPATH isn't inserted into, resulting in this error.

Please see our GCC upgrade guide for what needs to be rebuilt after a GCC upgrade.

In some rare cases, this can break old versions of python, too. This may be fixed by adding (change accordingly to the old   and gcc version) to, running ldconfig and then emerge libstdc++-v3. However, as can be seen, this situation needs to be avoided - don't change  and gcc at the same time.

Feedback
That should be all, feedback (both if it worked, failed or other problems were encountered) is welcome, please send an email to or post to this forums thread. Much in this howto comes from vapier, thanks for your help!