How to build s390x emulator (tcg) on Ubuntu 16.04:

1. Download qemu's source code using apt::

.. code:: shell

  $ apt source qemu
  
2. Install all build requirements according to [1]::

.. code:: shell

  $ sudo mk-build-deps -i -r qemu
  
3. Install s390x cross compiler::

.. code:: shell

  $ sudo apt install -y gcc-5-multilib-s390x-linux-gnu
  
4. Change debian/rules to always build s390x bootloader via cross-compiler, by applying the provided patch::

.. code:: shell

  $ cd qemu-2.5+dfsg
  $ patch -p1 < ~/qemu-s390x-debian-rules.patch

5. Build according to [1], this will take some time::

.. code:: shell

 $ fakeroot debian/rules binary
 ...
 
6. Install resulting `qemu-system-s390x` package::

.. code:: shell

 $ sudo apt install ../qemu-system-s390x_2.5+dfsg-5ubuntu10.14_amd64.deb
 
7. Use `virt-manager`[2] to setup the host, don't use CDROMs as they are not supported.
   Rather, download and use latest debian's installer kernel and initrd::

.. code:: shell

 $ wget -c http://ftp.debian.org/debian/dists/stable/main/installer-s390x/current/images/generic/kernel.debian \
   http://ftp.debian.org/debian/dists/stable/main/installer-s390x/current/images/generic/initrd.debian
   
8. Use above as initrd and kernel on 'Boot Options' tab  under 'Direct kernel boot'. Installation only possible via console.

[1] https://wiki.debian.org/BuildingAPackage

[2] https://virt-manager.org/