Changing the CHOST variable

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 a system - so why is there a guide for that if it can cause that much havoc?

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

Even after following these instructions, problems may arise, so please make sure to read and execute them very carefully. In this example the CHOST variable will be changed from i386 to i686. Please change the commands according to the specific situation.

Updating make.conf
To start out with the CHOST variable change, edit the file and add/change the CHOST value to suit the requirements.

Please note that if you are planning to use another value of CHOST than the profile default, you may need to update the CHOST_${ABI} variable as well. You can query the current value of these variable via portageq tool:

If this value is equal to your CHOST, you're good. Otherwise, you should override it as well, e.g.:

Building the packages
Rebuild the following packages in this order:

Verifying things work
Now it is time to make sure that the and  settings are sane and that there are no leftovers in.

The output of and  should look like the following:

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

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

This one looks good as there should always be only one file for  in  ( in this example), so 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The same also applies to - if there's an extra one, see which is the outdated one and delete it.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 the contents of :

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

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

Now run the following commands to update the environment:

Next, verify everything is fixed:

If there are still files found, try to track it down before going on.

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

It is now possible to rebuild all the packages:

In theory, it should not be necessary to do so, but it cannot be 100% guaranteed that this is actually the case. Alternatively, you can manually rebuild all the known problematic packages:
 * multilib packages using CHOST prefixing or header wrapping,
 * Perl, Python and other tools that store configured compiler path.

Note that you may need to remove paths that do not apply to your system from the above invocation.

When encountering other packages that need recompiling, please let us know through the discussion page of this guide.

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

This happens because during the upgrade, the CHOST variable doesn't exactly match the CTARGET variable value, making the compiler assume that the system is using cross-compiling. As a consequence, LDPATH isn't inserted into, resulting in this error.

Please see the 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 CHOST and gcc version) to, running  and then. However, as can be seen, this situation needs to be avoided - don't change CHOST 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 use the discussion page or post to this forum thread. Much in this guide comes from vapier, thanks for your help!