Linux Device Driver Development Cookbook

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Installing and configuring schroot

This task is quite trivial in Ubuntu:

First of all, we install the program in the usual way:

$ sudo apt install schroot

Then, we have to configure it in order to correctly enter into our ARM64 system. To do so, let's copy the root filesystem created before into a dedicated directory (where we can also add any other distributions we wish to emulate with schroot):

$ sudo mkdir /srv/chroot/
$ sudo cp -a debian-stretch-arm64/ /srv/chroot/

Then, we must create a proper configuration for our new system by adding a new file into the schroot configuration directory, as follows:

$ sudo bash -c 'cat > /etc/schroot/chroot.d/debian-stretch-arm64 <<__EOF__
[debian-stretch-arm64]
description=Debian Stretch (arm64)
directory=/srv/chroot/debian-stretch-arm64
users=giometti
#groups=sbuild
#root-groups=root
#aliases=unstable,default
type=directory
profile=desktop
personality=linux
preserve-environment=true
__EOF__'

Note that the directory parameter is set to the path holding our ARM64 system and users is set to giometti, which is my username (this is a comma-separated list of users that are allowed access to the chroot environment—see man schroot.conf).

Looking at the preceding settings, we see that the profile parameter is set to desktop; this means that it will be taking into account all files in the /etc/schroot/desktop/ directory. In particular, the fstab file holds all mount points we'd like to be mounted into our system. So, we should verify that it holds at least the following lines:

# <filesystem> <mount point> <type> <options> <dump> <pass>
/proc           /proc         none   rw,bind   0      0
/sys            /sys          none   rw,bind   0      0
/dev            /dev          none   rw,bind   0      0
/dev/pts        /dev/pts      none   rw,bind   0      0
/home           /home         none   rw,bind   0      0
/tmp            /tmp          none   rw,bind   0      0
/opt            /opt          none   rw,bind   0      0
/srv            /srv          none   rw,bind   0      0
tmpfs           /dev/shm      tmpfs  defaults  0      0

Now, we have to restart the schroot service, as follows:

$ sudo systemctl restart schroot

Note that you can also restart using the old-fashioned way:
$ sudo /etc/init.d/schroot restart

Now we can list all available environments by asking them to schroot, as follows:

$ schroot -l
 chroot:debian-stretch-arm64

OK, everything is in place and we can enter into the emulated ARM64 system:

$ schroot -c debian-stretch-arm64
bash: warning: setlocale: LC_ALL: cannot change locale (en_GB.UTF-8)

Since we haven't installed any locale support, the preceding warning is quite obvious and it should be safely ignored.

Now, to verify we're really executing ARM64 code, let's try some commands. For example, we can ask for some system information with the uname command:

$ uname -a
Linux giometti-VirtualBox 4.15.0-43-generic #46-Ubuntu SMP Thu Dec 6 14:45:28 UTC 2018 aarch64 GNU/Linux

As we can see, the system says that its platform is aarch64, which is ARM64. Then, we can try to execute our helloworld program that was cross-compiled before; since, after chroot, the current directory is not changed (and our home directory is still the same), we can simply go back where we did the compilation and then execute the program as usual:

$ cd ~/Projects/ldddc/github/chapter_1/
$ file helloworld
helloworld: ELF 64-bit LSB shared object, ARM aarch64, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux-aarch64.so.1, for GNU/Linux 3.7.0, BuildID[sha1]=c0d6e9ab89057e8f9101f51ad517a253e5fc4f10, not stripped
$ ./helloworld
Hello World!

The program still executes as when we were on an ARM64 system. Great!