11. App - Development

11.1 Objectives

Compile and run your own ncurses application on the target.

11.2 Required tools

Our cross-compile toolchain
Ubuntu packages: those from the previous labs.

11.3 Setup

Go to the $HOME/embedded-linux-qemu-labs/appdev directory.

$ LAB_PATH="$HOME/embedded-linux-qemu-labs/appdev"

11.4 Compile your own application

In the lab directory, the file app.c contains a very simple ncurses application. It is a simple game where you need to reach a target using the arrow keys of your keyboard. We will compile and integrate this simple application to our Linux system.

We will re-use the system built during the Buildroot lab and add to it our own application. Buildroot has generated toolchain wrappers in output/host/bin, which make it easier to use the toolchain, since these wrappers pass some mandatory flags (especially the --sysroot GCC flag, which tells GCC where to look for the headers and libraries).

Let’s add this directory to our PATH.
NOTE: the Buildroot GCC wrappers MUST take priority over our toolchain, otherwise these wrappers won't be called!

$ export PATH="$HOME/embedded-linux-qemu-labs/buildroot/buildroot/output/host/bin:$PATH"
$ which arm-linux-gcc
/home/me/embedded-linux-qemu-labs/buildroot/buildroot/output/host/bin/arm-linux-gcc

Let’s try to compile the application.
It should complain about undefined references to some symbols. This is normal, since we didn’t tell the compiler to link with the necessary libraries.

$ cd $LAB_PATH
$ arm-linux-gcc -o app app.c
    ...
app.c:(.text+0x30): undefined reference to `initscr'
    ...
collect2: error: ld returned 1 exit status

So, let’s use pkg-config to query the pkgconfig database about the location of the header files and the list of libraries needed to build an application against ncurses.
There's indeed a special pkg-config under output/host/bin/ that automatically knows where to look, so it already knows the right paths to find .pc files and their sysroot.

$ which pkg-config
/home/me/embedded-linux-qemu-labs/buildroot/buildroot/output/host/bin/pkg-config
$ pkg-config --libs --cflags ncurses
-D_GNU_SOURCE -lncurses
$ arm-linux-gcc -o app app.c $(pkg-config --libs --cflags ncurses)

Our application is now compiled! Copy the generated binary to the NFS root filesystem (in the root/ directory for example), start your system, and run your application!

$ cp app "$LAB_PATH/../buildroot/nfsroot/root/"

QEMU - Buildroot

# /root/app
                                 Hello World!






                                 X



                                       O











Move to the target (X), 'q' to quit

11.5 Backup and restore

$ cd $LAB_PATH
$ tar cfJv app.tar.xz app
$ cd "$LAB_PATH/../buildroot/nfsroot/"
$ find . -depth -print0 | cpio -ocv0 | xz > "$LAB_PATH/nfsroot-appdev.cpio.xz"