#Installing a Cross-compiling toolchain on Gentoo Linux

These instructions explain how to install a toolchain for compiling 32bit and 64bit windows programs using Gentoo Linux and the crossdev tool. Most of the steps in this instruction should be either performed as root, or with a sudo prefix.

I install toolchains for both 32bit (the i686-pc-mingw32 target) and 64bit (the x86_64-pc-mingw32 target) windows. The instructions below include commands to install both targets, however, if you wish to install just one environment, feel free to skip the commands with the other.

Crossdev Repository

First, we need to make a repository for portage and crossdev to store package information (see the Crossdev section of the Gentoo local overlay wiki for more details). I place all my local repositories in the /usr/local/portage directory, with each local repository as a subdirectory. I call my crossdev repository local-crossdev, and it is stored in /usr/local/portage/crossdev. To tell portage about this setup, create /usr/portage/repos.conf/local-crossdev.conf with the following contents:

[local-crossdev]
priority = 9999
masters = gentoo
auto-sync = no
location = /usr/local/portage/crossdev

Create the directory pointed to by the location parameter:

mkdir -p /usr/local/portage/crossdev

Fresh install

Whenever a new gcc version is released (made stable by crossdev), I like to completely remove my old toolchain environment and start fresh. This helps clean out some libraries that I need to install manually (like boost), that portage isn't aware of. So let's start off by deleting the old environment(s).

crossdev -C x86_64-pc-mingw32
crossdev -C i686-pc-mingw32

If crossdev asks if you want to delete the directory, answer yes.

Initialize new environment

Setup in new toolchain environment(s) with:

crossdev -t x86_64-pc-mingw32 --stable --init-target -oO /usr/local/portage/crossdev
crossdev -t i686-pc-mingw32 --stable --init-target -oO /usr/local/portage/crossdev

where the directory after -oO should be the same as the location parameter in repo.conf

To use only packages from the stable branch, edit /usr/<target>/etc/portage/make.conf and remove the unstable branch from ACCEPT_KEYWORDS (~amd64, ~x86). The <target> tag should be replaced with x86_64-pc-mingw32, i686-pc-mingw32, or any other target you wish to install.

Make sure gcc is not compiled with the sanitize or vtv flags.

echo "cross-x86_64-pc-mingw32/gcc -sanitize -vtv" >> /etc/portage/package.use/crossdev
echo "cross-i686-pc-mingw32/gcc -sanitize -vtv" >> /etc/portage/package.use/crossdev

Install environment

Now we can finally install the environment. Issue the following commands and wait for them to complete.

crossdev -t x86_64-pc-mingw32 --stable -oO /usr/local/portage/crossdev
crossdev -t i686-pc-mingw32 --stable -oO /usr/local/portage/crossdev

Extra packages

bzip2

Bzip2 fails to compile for i686-pc-mingw32, the ftello() and fseeko() routines must be changed to ftello64() and fseeko64(), respectively. To do this, we will instruct portage to apply a patch when it installs bzip2. First, make the directory structure where the patch will be placed:

mkdir -p /usr/i686-pc-mingw32/etc/portage/patches/app-arch/bzip2

and now copy the patch from bzip2/ftello64-fseeko64.patch into the newly created directory.

cp bzip2/ftello64-fseeko64.patch /usr/i686-pc-mingw32/etc/portage/patches/app-arch/bzip2/

We also need to little script to instruct portage to apply our patch. Copy bashrc from bzip2/bashrc:

cp -p bzip2/bashrc /usr/i686-pc-mingw32/etc/portage/bashrc

That should let bzip2 install when emerging the Boost library

Boost library

Boost will fail to compile with emerge, but this will install dependencies like zlib and bzip2, and download the tarball to portage DISTDIR for us.

USE="static-libs" ARCH=amd64 x86_64-pc-mingw32-emerge -avt boost
USE="static-libs" ARCH=x86   i686-pc-mingw32-emerge   -avt boost

Let emerge run until it fails on boost, all the required packages should then be installed and we can go ahead and install boost manually.

As a side note, it is convenient to know a way to show which packages have been installed via emerge into our toolchain environments:

ROOT=/usr/x86_64-pc-mingw32 eix -I --only-names
ROOT=/usr/i686-pc-mingw32   eix -I --only-names

Manually install Boost

Extract the boost tarball that was downloaded into portage DISTDIR.

tar -xjf boost_1_56_0.tar.bz2

The name of your boost tarball may be different than shown here, if you have a different version. Extract whatever version emerge downloaded for you.

Go into the directory that was extracted

cd boost_1_56_0

Again, the directory name may be different than yours if you got another version of boost.

Now, to help install boost I have a little script which I call crossdev-boost.sh. Run that script while still in the boost extracted directory and it will guide you through the compiling and installation process. Run the script multiple times to install for more toolchain environments. If you downloaded crossdev-boost.sh into your home directory, then use

~/crossdev-boost.sh

winpthreads

To install winpthreads, first download the latest version of MinGW-w64. Then extract the package, compile winpthreads, and install following these instructions (replace v3.2.0 with the version you downloaded):

tar -xjf mingw-w64-v3.2.0.tar.bz2
cd mingw-w64-v3.2.0/mingw-w64-libraries/winpthreads
TARGET=x86_64-pc-mingw32 && ./configure --prefix=/usr/$TARGET/usr --host=$TARGET --target=$TARGET --enable-static --disable-shared
make
sudo make install

Make sure TARGET is set appropriately.

CMake

To cross-compile with cmake use the appropriate toolchain file and invoke cmake with

cmake -DCMAKE_TOOLCHAIN_FILE=x86_64-pc-mingw32.cmake ...

replacing ... with the cmake parameters needed for your particular project, and x86_64-pc-mingw32.cmake with the file downloaded from toolchain.