= Cross-compiling Synapse for raspberry (ARM) and other architectures =

This is a quick howto on how i cross compiled synapse for the raspberrypi, using qemu to emulate the arm cpu architecture. This is the least tricky methode to cross compile, but also the slowest.

I used arch linux on my host system and debian on the rasp.

== Learn your host system how to handle arm binaries ==

=== 1. Steal a statically compiled qemu-arm from some distro: ===

its a shame archlinux doesnt have a static qemu :(

{{{
[root@lab1 tmp]# cd /tmp
[root@lab1 tmp]# mkdir qemu
[root@lab1 tmp]# cd qemu
[root@lab1 qemu]# dpkg -x /home/psy/Downloads/qemu-user-static_1.1.2+dfsg-2_amd64.deb  .
[root@lab1 qemu]# cp usr/bin/qemu-*-static /usr/bin
}}}

=== 2. learn your kernel how to handle arm binaries ===

{{{
[root@lab1 binfmts]# cat /usr/share/binfmts/qemu-arm          
package qemu
interpreter /usr/bin/qemu-arm-static
magic \x7fELF\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x28\x00
mask \xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff

[root@lab1 binfmts]# update-binfmts --import

}}}


== Set up the build environment ==

=== 1. copy the rootfilesystem from your raspberry ===

We just copy the whole rootfs, so we have an exact copy of the environment we want to cross compile for:

{{{
[root@lab1 psy]# rsync -ax root@192.168.13.238:/ rasprootfs
root@192.168.13.238's password: 
....
}}}


=== 2. entering the build environment ===

The only thing you have to do to be able to enter the environent is copy qemu-arm-static into it:

{{{
[root@lab1 psy]# cp /usr/bin/qemu-arm-static rasprootfs/usr/bin/
[root@lab1 psy]# chroot rasprootfs/
root@lab1:/# uname -a
Linux lab1 3.6.5-1-ARCH #1 SMP PREEMPT Wed Oct 31 20:57:39 CET 2012 armv7l GNU/Linux
}}}}

w000h...now we can chroot to the local raspberry environment and start to compile stuff!