Changing the CHOST variable

From Gentoo Wiki
Jump to:navigation Jump to:search

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

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. Most of them should never be necessary in normal operations (e.g., because they involve bootstrapping for a new architecture). Sometimes however... As an example, switching profile may involve a change of CHOST, e.g., in the case of the upgrade of MIPS machines from the 17.0 to the 23.0 profiles, because we are adapting our settings to common standards.

Even after following the instructions here, problems may arise, so please make sure to read and execute them very carefully. In this example the CHOST variable will be changed from mips64-unknown-linux-gnu to mips64-unknown-linux-gnuabin32. Please change the commands according to the specific situation.

Updating make.conf

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

FILE /etc/portage/make.conf

Note that profiles provide a default setting for CHOST; depending on the situation, it may be necessary to override it in /etc/portage/make.conf or remove an override in /etc/portage/make.conf. In any case, the important point is that the effective value changes.

Please note that if planning to use another value of CHOST than the profile default, the CHOST_${ABI} variable may need updating as well. It is possible to query the value of this variable of the currently set profile with the portageq tool:

user $portageq envvar ABI
user $portageq envvar CHOST_n32

If this value is equal to CHOST, it's good. Otherwise, override it as well, e.g.:

FILE /etc/portage/make.conf

Building the packages

It is generally a good idea to rebuild the packages to the same versions as before the CHOST switch, i.e. avoiding combining upgrades with it. If multiple slots are installed, either uninstall extraneous slots or rebuild all of them. If that is not possible, please upgrade the packages first (with old CHOST). While it may not be impossible to do so, it is hard to predict which potential problems may arise and almost impossible to document them in this guide.
If the CHOST switch takes place together with other changes, e.g. in the course of a profile upgrade, please read the documentation there as well to make sure the different steps do not interfere.

Rebuild the following packages in this order:

root #emerge --ask --oneshot sys-devel/binutils
It may be necessary to run binutils-config before compiling gcc.
root #emerge --ask --oneshot sys-devel/gcc

For glibc based systems:

root #emerge --ask --oneshot sys-libs/glibc

For musl based systems:

root #emerge --ask --oneshot sys-libs/musl

Verifying things work

Now it is time to make sure that the gcc-config and binutils-config settings are sane and that there are no leftovers in /etc/env.d/.

The output of gcc-config and binutils-config should look like the following:

The output may, or even will differ according to the gcc version and CHOST settings. The example below uses gcc 12 on mips.
root #gcc-config -l
 [1] mips64-unknown-linux-gnuabin32-12 *
root #gcc-config -c
root #binutils-config -l
 [1] mips64-unknown-linux-gnuabin32-2.39 *
# binutils-config -c

Next, check to see if there are references to the old CHOST variable in /etc/env.d/:

root #cd /etc/env.d/
root #grep linux-gnu *

Here, binutils is fine - there is one file, and it only contains references to the new CHOST. For gcc, there is a file for both the new and the old CHOST value, so delete the old stale one:

root #rm 04gcc-mips64-unknown-linux-gnu

The same also applies to binutils - if there's an extra one, see which is the outdated one and delete it. Next, check the contents of /etc/env.d/binutils/:

root #cd /etc/env.d/binutils/
root #ls -l
total 12
-rw-r--r-- 1 root root  13 Dec  9 22:16 config-mips64-unknown-linux-gnu
-rw-r--r-- 1 root root  13 Dec 31 17:00 config-mips64-unknown-linux-gnuabin32
-rw-r--r-- 1 root root 117 Dec 31 16:59 mips64-unknown-linux-gnuabin32-2.39
root #cat config-mips64-unknown-linux-gnuabin32
root #cat mips64-unknown-linux-gnuabin32-2.39

There's one stale file with the old CHOST, config-mips64-unknown-linux-gnu, so delete this one.

root #rm config-mips64-unknown-linux-gnu

Time to move on to the gcc/ directory.

root #cd /etc/env.d/gcc
# ls -l
total 12
-rw-r--r-- 1 root root  36 Dec 30 11:31 config-mips64-unknown-linux-gnu
-rw-r--r-- 1 root root  42 Dec 31 23:54 config-mips64-unknown-linux-gnuabin32
-rw-r--r-- 1 root root 353 Dec 31 23:52 mips64-unknown-linux-gnuabin32-12
root #cat config-mips64-unknown-linux-gnuabin32
root #cat config-mips64-unknown-linux-gnu
root #cat mips64-unknown-linux-gnuabin32-12

config-mips64-unknown-linux-gnuabin32 and mips64-unknown-linux-gnuabin32-12 are fine, but config-mips64-unknown-linux-gnu is another leftover that needs removal.

Again, the name of the file containing references to an outdated gcc version may have a different name. It is important to identify the file on its content, not only the name.
root #rm config-mips64-unknown-linux-gnu

Now run the following commands to update the environment:

root #env-update && source /etc/profile

Next, verify everything is fixed in /etc/env.d. If there are still files found, try to track it down before going on.

Finishing the change

Now it is necessary to re-emerge sys-devel/libtool:

root #emerge --ask --oneshot libtool

It is now possible to rebuild all the packages:

root #emerge --ask --emptytree @world

In theory, it should not be necessary to do so, but it cannot be 100% guaranteed that this is actually the case. Alternatively, it is possible to 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.
root #emerge --ask --oneshot /usr/bin/mips64-unknown-linux-gnu-* /usr/include/mips64-unknown-linux-gnu /usr/lib/llvm/*/bin/mips64-unknown-linux-gnu-* dev-lang/perl dev-lang/python

Note that paths that do not apply to the current system may need removing from the above invocation.

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

Common problems

Not so many anymore. Usually this just works, as long as no really exotic change is done. Make sure to not combine the CHOST change with other steps though. Some of the notes below are really old...

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 sys-apps/groff and mail-mta/courier:

CODE Error message
error while loading shared libraries: cannot open shared object file: No such file or directory

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 /usr/lib/gcc-lib/i386-pc-linux-gnu/3.3.6 (change accordingly to the old CHOST and gcc version) to /etc/, running ldconfig and then emerge libstdc++-v3. However, as can be seen, this situation needs to be avoided - don't change CHOST and gcc at the same time.


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 the help!

This page is based on a document formerly found on our main website
The following people contributed to the original document: Wernfried Haas, Mike Frysinger (vapier) , Chris White
They are listed here because wiki history does not allow for any external attribution. If you edit the wiki article, please do not add yourself here; your contributions are recorded on each article's associated history page.