Multiarch: Adding another target architecture

This is a short guide on how to enable another target architecture using the armv7-unknown-linux-gnueabihf architecture as an example. You can see all currently supported targets by looking at target options reported by

    # cave show gcc::arbor

If you expect you’ll need a different set of options for the new target, consider adding it in a another paludis environment.

Configure the target suboption in /etc/paludis/options.conf
```
* /etc/paludis/options.conf *

*/* targets: armv7-unknown-linux-gnueabihf
```
Make sure not to remove your native target, i.e. the one matching your CHOST.

Setup *FLAGSS in /etc/paludis/bashrc

* /etc/paludis/bashrc *

armv7_unknown_linux_gnueabihf_CFLAGS="-pipe -O2 -march=armv7-a -mtune=cortex-a9 -mfloat-abi=hard -mfpu=vfpv3"
armv7_unknown_linux_gnueabihf_CXXFLAGS="-pipe -O2 march=armv7-a -mtune=cortex-a9 -mfloat-abi=hard -mfpu=vfpv3"

These flags are just a suggestion and you most certainly want to change them to match your hardware (the ones above are suitable for a TI OMAP4). gcc’s documentation lists possible options.

Add a config file for the target’s installed repository

tool_prefix is the prefix for the toolchain components which is being used to generate the binaries for the target platform, armv7-unknown-linux-gnueabihf- in our case.

split_debug_location is the location where the split debug information is stored for the packages that are installed.

cross_compile_host is the target host on which the binaries will run.
```
* /etc/paludis/repositories/armv7-unknown-linux-gnueabihf.conf *

format = exndbam
location = ${root}/var/db/paludis/repositories/cross-installed/armv7-unknown-linux-gnueabihf
name = armv7-unknown-linux-gnueabihf
split_debug_location = /usr/armv7-unknown-linux-gnueabihf/lib/debug
tool_prefix = armv7-unknown-linux-gnueabihf-
cross_compile_host = armv7-unknown-linux-gnueabihf
```
The directory specified by the location option above needs to be created:
```
# mkdir /var/db/paludis/repositories/cross-installed/armv7-unknown-linux-gnueabihf
```

Build binutils with the new target

# cave resolve --preserve-world binutils

Build gcc[-threads] (threading support requires libc which is not present in target yet)
```
* /etc/paludis/options.conf *

sys-devel/gcc -threads

# cave resolve --preserve-world sys-devel/gcc
```
This will also pull in eclectic-gcc.
Cross compile linux-headers and glibc
```
 # cave resolve --preserve-world --make cross-compile sys-kernel/linux-headers
 # cave resolve --preserve-world --make cross-compile --no-dependencies-from sys-libs/glibc sys-libs/glibc
```
Dependencies handling isn’t perfect. glibc has a run-time dependency upon timezone-data, but for cross compilation hosts that can’t be built before gcc. Therefore we have to use --no-dependencies-from.

If you have more than one cross compilation target in the same environment you’ll need to specify --cross-host armv7-unknown-linux-gnueabihf additionally.
Build gcc[threads]

Enable gcc’s threads option again by removing the previously added temporary sys-devel/gcc -threads from /etc/paludis/options.conf (it’s set by our profiles) and rebuild sys-devel/gcc afterwards:
```
 # cave resolve --preserve-world gcc --no-follow-installed-dependencies
```

Cross compile language runtimes.

 # cave resolve --preserve-world --make cross-compile libatomic libgcc libstdc++

Rebuild other packages having a targets suboption

pkg-config/pkg-conf also have a targets suboption and also need a rebuild. There are more packages, like clang for example, which also offer said option. You can use cave to find out and rebuild them or fine-tune your targets for these packages.
```
 # cave resolve --complete installed-slots
```
Start cross compiling other packages

Now that the toolchain is built and installed you can start building the packages you’re interested in for the new target:
```
# cave resolve --make cross-compile <foo>
```

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