How to build an executable for Android shell
The answer provides a sequence of steps for building an executable for Android shell
through both Eclipse
(outdated) and Android Studio
(4.1+ by the time of this writing). The last includes ndk-build
and CMake
.
I. PREPARE SOURCE CODE
As an example consider mycommand.c
:
#include <stdio.h>
int main()
{
printf("My Command!\n");
return 0;
}
II. BUILD EXECUTABLE
Eclipse (might be outdated)
In assumption that NDK
location is set in Eclipse
, create a new Android Application Project
and do the following steps.
Add native support. Right click on the project in
Project Explorer
>Android Tools
>Add Native Support
>Finish
Add source code, i.e. put
mycommand.c
underproject_root
/jni
folder.Edit
Android.mk
underproject_root
/jni
as follows:LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
LOCAL_MODULE := mycommand
LOCAL_SRC_FILES := mycommand.c
include $(BUILD_EXECUTABLE)Create
Application.mk
* under theproject_root
/jni
folder:APP_ABI := all
Build executable and find it under
project_root/libs/<abi>/mycommand
.
*Binaries for all
supported CPU architectures are generated here. Use adb shell cat /proc/cpuinfo
to find out the CPU architecture and set APP_ABI
as per Supported ABIs.
Android Studio and ndk-build
The steps are as follows.
Add
mycommand.c
,Android.mk
(same as in theEclipse
section above) to the/app/src/main/cpp
folder.Edit
build.gradle
:android {
...
defaultConfig {
...
externalNativeBuild {
ndkBuild {
targets "mycommand"
// use a specific ABI filter if needed
// abiFilters "armeabi-v7a"
}
}
}
externalNativeBuild {
ndkBuild {
path "src/main/cpp/Android.mk"
}
}
}Build project and find the executable under
/app/.externalNativeBuild/ndkBuild/debug/obj/local/<abi>/mycommand
Android Studio and CMake
Create a project using the Native C++ template.
Add
mycommand.c
to the/app/src/main/cpp
folder and editCMakeLists.txt
:cmake_minimum_required(VERSION x.x.x)
add_executable(mycommand
mycommand.c )Edit
build.gradle
:android {
...
defaultConfig {
...
externalNativeBuild {
cmake {
targets "mycommand"
// use a specific ABI filter if needed
// abiFilters "armeabi-v7a"
}
}
}
...
externalNativeBuild {
cmake {
path "src/main/cpp/CMakeLists.txt"
}
}
}Build project and find the executable under
/app/build/intermediates/cmake/debug/obj/<abi>/mycommand
III. PUSH BINARY INTO DEVICE
Push mycommand
binary from where it is located into your device. Keep in mind that files on SD card aren't executable by default, so the binary should be pushed into the device's internal storage. Depending of whether device is rooted or not you have the following options:
On non-rooted device you can push the binary to
/data/local/tmp
:adb push mycommand /data/local/tmp
On rooted device you can push the binary to SD card and then copy it to
/system/bin
(after remounting the partition in read-write mode) along with the other executable files:adb push mycommand /path/to/sdcard
adb shell
su
mount -o rw,remount /system
cp /path/to/sdcard/mycommand /system/bin
IV. SET EXECUTABLE PERMISSION (optional)
Set the permission of the binary to be executable (this might not be needed in case of /data/local/tmp
). Below chmod 555
(r-xr-xr-x) is used:
adb shell chmod 555 /path/to/mycommand
V. RUN COMMAND
Now you can shell into your device (with adb shell
) and execute the command.
On non-rooted device use the absolute path to the command:
$ /data/local/tmp/mycommand
My Command!On rooted device, in case the binary has been copied to
/system/bin
, you can call it by the file name:$ mycommand
My Command!
Compile and run C code for Android
Let's start from the bottom up.
Going C (or C++) does not grant your code extra rights under Android.
There are different options of doing all your development without Java. There are frameworks for pure C++ (like NativeActivity), or for C# (MonoDroid), or Scala, or Ruby, or whatnot.
Android NDK also allows to simply build an executable - one that can be run from command line, and has no GUI. Your Android app can launch such executable via standard Java Runtime.exec()
and her siblings. Or you can launch this executable from a terminal emulator or adb shell
.
If you have root access on your device (or if you flash your own mod), you can launch an executable through the standard Linux init.rc
or similar.
Note that in the latter case, you can easily grant your executable root
or other permissions.
Want to compile native Android binary I can run in terminal on the phone
Just use the android-ndk. And build a Android.mk like so.include $(BUILD_EXECUTABLE)
is what tells it build a executable instead of a JNI .lib
Android.mk
ifneq ($(TARGET_SIMULATOR),true)
LOCAL_PATH:= $(call my-dir)
include $(CLEAR_VARS)
LOCAL_CFLAGS += -Wall
LOCAL_LDLIBS := -L$(LOCAL_PATH)/lib -llog -g
LOCAL_C_INCLUDES := bionic
LOCAL_C_INCLUDES += $(LOCAL_PATH)/include
LOCAL_SRC_FILES:= main.cpp
LOCAL_MODULE := mycmd
include $(BUILD_EXECUTABLE)
endif # TARGET_SIMULATOR != true
Execute a pure binary file on Android
adb push exename /data/bin/exename
#next line might be needed if you are developing on Windows
adb shell chmod 777 /data/bin/exename
adb shell /data/bin/exename
But your device has to be rooted. (It also works on emulator.)
Can I use printf in an Android native binary
#include <stdio.h>
int main() {
printf("Hello, world\n");
return 0;
}
Then:
~/Library/Android/sdk/ndk/24.0.8215888/toolchains/llvm/prebuilt/darwin-x86_64/bin/clang --target=aarch64-linux-android21 helloworld.c -o helloworld
adb push helloworld /data/local/tmp/helloworld
adb shell /data/local/tmp/helloworld
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