Upgrade GCC up to 4.1

This document will guide the user through the process of upgrading GCC.

GCC Upgrading
Why should you upgrade? Well, GCC is quite similar to any other package on your system, just a bit more critical. You should upgrade GCC whenever a new version fixes some bug that annoys you, new functionality you need is introduced, or if you want to keep your system up-to-date. If none of the previous cases apply to you, you can safely postpone upgrade as long as your GCC version is supported by Gentoo developers.

If you install a new major version of GCC (such as 3.3.6 to 3.4.5), the system will not switch over to use it automatically. You'll have to explicitly request the change because the migration process might require some additional steps. If you decide not to switch, Portage will continue to use older version of your compiler until you change your mind, or remove the old compiler from the system. Non-major gcc upgrades are switched automatically for you (such as 3.4.5 to 3.4.6).

This guide will document the necessary steps required to perform a seamless upgrade of the compiler used by your Gentoo box. A specific section is dedicated to the and issues with. A second specific section is for users Gentoo using a stage3 tarball, after a new GCC major/minor version has been released.

Introduction
Generally speaking, upgrades to bug fix releases, like from 3.3.5 to 3.3.6, should be quite safe -- just emerge new version, switch your system to use it and rebuild the only affected package,. However, some GCC upgrades break binary compatibility; in such cases a rebuild of the affected packages (or even whole toolchain and system) might be required.

When we spoke about the need to switch your compiler to the newer version by hand, we said it won't happen automatically. However, there is one exception -- upgrades to bug fix releases, like from 3.3.5 to 3.3.6 in case you don't use the "multislot" feature allowing them to coexist on one system. Multislot is disabled by default as the majority of users won't benefit from it.

Please substitute "i686-pc-linux-gnu-4.1.1" with the GCC version and CHOST settings you've upgraded to:

If you upgraded from gcc 3 to 4 (e.g. from 3.4.6 to 4.1.1 in this example) you will have to run fix_libtool_files.sh manually. Replace $CHOST with your actual CHOST, found in /etc/portage/make.conf. Replace  with your new, updated GCC version.

Now rebuild libtool.

To be completely safe that your system is in a sane state, you must rebuild the toolchain and then world to make use of the new compiler.

It is safe to remove the older GCC version at this time. If you feel the need, please issue the following command (as usual, substitute  with the version you want to uninstall):

Introduction
The upgrade from GCC-3.3 to 3.4 is not seamless as the C++ ABI changed between these two versions. There is an issue with the  library which must be taken care of, as well.

The Choices
If you upgrade from gcc 3.3 to 3.4, you have two possibilities on how to upgrade your system. The revdep-rebuild method is faster and requires use of the  tool from package   while the other option rebuilds the entire system from scratch so it will make use of new GCC features. It's up to you to decide which of these two ways you will choose. In most cases, the first method is sufficient.

If you upgrade from gcc 3.3 to 4.1, do not use the method based on revdep-rebuild, but rebuild the entire system.

Using revdep-rebuild
This method requires that you first install  if you have not already done so. Then we will upgrade GCC and switch to the new compiler. We will also rebuild the  package to ensure that toolchain is in healthy state.

Please substitute "i686-pc-linux-gnu-3.4.5" with the GCC version and CHOST settings you've upgraded to:

Now rebuild libtool.

Now, we want to see which packages that revdep-rebuild will want to rebuild. Then we will tell revdep-rebuild to actually rebuild the packages. This may take some time, so have some patience.

To provide compatibility with older binary C++ applications and any packages that revdep-rebuild might have missed,  needs to be merged before you unmerge GCC 3.3 from your system.

Using emerge -e
This method, while much slower, will rebuild your whole system to ensure that everything has been rebuilt with your new compiler, and therefore safer. At first, you will upgrade GCC and libtool and switch to your new compiler.

Please substitute "i686-pc-linux-gnu-3.4.5" with the GCC version and CHOST settings you've upgraded to:

If you upgraded from gcc 3 to 4 (e.g. from 3.3.6 to 4.1.1 in this example) you will have to run fix_libtool_files.sh manually. Replace $CHOST with your actual CHOST, found in /etc/portage/make.conf. Replace  with your new, updated GCC version.

To provide compatibility with older binary C++ applications,  needs to be merged onto your system.

Now we will go about first rebuilding the system target, then the world target. This will take a very long time, depending on the number of packages that you have installed, as it will rebuild your entire toolchain and supporting system files, followed by every package on your system, including the toolchain. This is necessary to ensure that all packages have been compiled with the new toolchain, including the toolchain itself.

It is also safe to remove older GCC versions at this time:

Introduction
A GCC upgrade on a system after installation from a stage3 tarball is a simple affair. One advantage users of new installations have is they do not have a plethora of software installed that links against the older version of GCC. The following example is for a GCC-3.3 to 3.4 upgrade. Certain parts will be different if upgrading from other versions of GCC. For example, the library names used for  below are GCC 3.3 specific, as well as the need to install.

If a user has not made any customizations to their system yet, then there are very few steps to get their system upgraded to a new GCC version. As with the GCC-3.3 to 3.4 upgrade, the user has a couple options. However, unlike the GCC-3.3 to 3.4 upgrade, this one is less complicated as there are fewer differences between the methods. The is faster and makes use of the   tool from  , similar to the above procedure. Using revdep-rebuild causes only packages which actually link against GCC libraries to be rebuilt, while the causes your entire new install to be recompiled with the new GCC version and takes much longer. This second method is never required and only documented for completeness.

These first steps are common between both methods, and should be completed by everyone.

Please substitute "i686-pc-linux-gnu-3.4.5" with the GCC version and CHOST settings you've upgraded to:

Now rebuild libtool.

To provide compatibility with older binary C++ applications,  needs to be merged onto your system.

Using revdep-rebuild
This method requires that you first install  if you have not already done so. We will then run  to actually scan the installed packages for ones we need to rebuild, then rebuild them.

Using emerge -e
This method, while much slower, will rebuild the system target to ensure that everything has been rebuilt with your new compiler. This is not necessary, but is valid if you are also making changes to CFLAGS or other make.conf variables that will affect the system compile.

Since we are performing these actions after an initial installation, we do not need to recompile the  target as we would when doing an upgrade on an already installed system. However, you may choose to perform a world update in place of the system update, to ensure that all packages are updated.

Cleaning up
It is also safe to remove older GCC versions at this time. Please substitute  with the actual version you've upgraded to:

Common Pitfalls
It's important to disable  during upgrade. Mixing compiler versions on your nodes will cause build issues. This is not required for ccache, as the cache objects will be invalidated anyway.

Always use same GCC version for your kernel and additional kernel modules. Once you rebuild your world with new GCC, external modules (like  ) will fail to load. Please rebuild your kernel with the new GCC to fix that.

If you're upgrading on a SPARC machine, make sure to rerun  after re-emerging world to avoid possible issues.

Frequent Error Messages
If your system complains about something like libtool: link: `/usr/lib/gcc-lib/i686-pc-linux-gnu/3.3.6/libstdc++.la' is not a valid libtool archive, please run  (substitute "3.3.6" with the version numbers from the error message, and $CHOST and  with your actual CHOST and GCC version).

If you see error: /usr/bin/gcc-config: line 632: /etc/env.d/gcc/i686-pc-linux-gnu-3.3.5: No such file or directory, then try deleting and running   again, followed by. Only do this if you do not have any cross-compilers set up, though.

If a package fails during  or  , you can resume operation with. If a package fails repeatedly, skip it with. Don't run any other instances of emerge in between or you will lose the resume information.

If you get an error message spec failure: unrecognized spec option while upgrading your compiler, try to switch back to your default compiler, unset the  variable and upgrade GCC again:

Acknowledgements
We would like to thank the following authors and editors for their contributions to this guide:


 * Wernfried Haas
 * Jan KundrÃ¡t
 * halcy0n
 * nightmorph