Android Development in C

This article just describes how to build a simple terminal application in C and C++ that finally runs on an Android device. GUI development is not addressed.

Prerequisites

Packages required for ARM development in C

Most Android devices are equipped with a APU utilizing ARM architecture. Therefore, binaries for ARM must be created. The following packages must be used on Debian systems to install compilers for C and C++:

• gcc-arm-linux-gnueabi
• g++-arm-linux-gnueabi

The program adb is required for communicating with the Android device. Package: android-tools-adb - Documentation can be found here.

Troubleshooting adb

If "adb devices" returns "???????????? no permissions", the following commands can help:

adb kill-server && adb start-server

This should be executed as root.

Credits

Mounting /system read-write

That's required to write binaries to /system/bin so they can be executed. Normally, /sdcard is mounted with noexec option, hence it doesn't qualify for starting binaries from there.

mount -o rw,remount /system

Terminal emulator on Android device

A terminal emulator can be used on the device to start programs.

• Android Terminal Emulator by Jack Palevich in Google Play Store
• Android Terminal Emulator by Jack Palevich in F-Droid Repo

Hello World example in C

helloworld.c

#include <stdio.h>

int main(int argc, char** argv) {
   printf("Hello world!\n");
   return 0;
}

Building and deploying

arm-linux-gnueabi-gcc -static helloworld.c -o helloworld
adb push helloworld /system/bin

Running

Either with adb shell /system/bin/helloworld or by executing it on the device using a terminal emulator.

Hello World example in C++

helloworldcpp.c++

#include <iostream>

using namespace std;

int main (int argc, char **argv)
{
	cout << "Hello World from C++!" << endl;
}

Building and deploying

arm-linux-gnueabi-g++ -static helloworldcpp.c++ -o helloworldcpp
adb shell /system/bin/helloworldcpp

Compiling GNU coreutils

Downloading

I am developing on Ubuntu 14.04 which ships with coreutils 8.21. coreutils have a lot of dependencies (like autoconf, autopoint, patch...), so to keep things simple, I grab the sources that match my operating system's version: coreutils_8.21.orig.tar.gz 11.7 MiB Download page

Customizing

After extracting the files from that archive, I do a "./configure" in the directory that contains the files. This process takes about 1 min 45 sec. After that it is important to customize the "Makefile": Search for a line containing

CC = gcc -std=gnu99

and replace it by

CC = arm-linux-gnueabi-gcc -std=gnu99 -static

Why "-static"? Otherwise the programs get linked dynamically, so they depend on the loader to resolve linked libraries. When testing on my Ubuntu machine, it was no problem:

qemu-arm -L /usr/arm-linux-gnueabi/ program

However, on my destination device running Cyanogenmod 9, I always get a "No such file or directory" error when trying to run those files.

Building

After doing a "make" - which runs about 2 min 30 sec - everything works fine. If you want to test if a program was linked statically or dynamically, use the file program:

file program

Example output:

$ file src/sleep
src/sleep: ELF 32-bit LSB  executable, ARM, EABI5 version 1 (SYSV), statically linked, for GNU/Linux 2.6.32, BuildID[sha1]=06a81ace0e2dabd5491dea6923ce0832295ba3f8, not stripped