How to build and use a shared libraries in Android

Actually, it is very simple to build and use your own shared library,

For the shared library, you need to create an Android.mk like this:

  LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)

  LOCAL_SRC_FILES := hello.c

  LOCAL_CFLAGS :=

  LOCAL_C_INCLUDES :=

  LOCAL_SHARED_LIBRARIES := libc        <=== may be not required 

  LOCAL_MODULE := libhello

  include $(BUILD_SHARED_LIBRARY)

For the executable that needs use this shared library, the Android.mk needs to be written as :

  LOCAL_PATH:= $(call my-dir)

  include $(CLEAR_VARS)

  LOCAL_SRC_FILES := main.c

  LOCAL_SHARED_LIBRARIES := libc libhello

  LOCAL_MODULE := myprog          <=== the name of final executable 

  include $(BUILD_EXECUTABLE)

Besides makefile changes, we also need to change build/core/prelink-linux-arm.map. Android does prelink (a modified version), all the memory location of DSO are predefined. In order to build a shared library for Android, you need to define the address and size for the memory used by your DSO (before you start to build anything). For current example, I have added following lines at the end of .map file.

  libhello.so            0x9A100000

  The C code I'm using to build this example is
main.c

  #include "myprog.h"

  int main(void)
{
    hello("World!");
    return 0;
}

  Hello.c
#include 

  void hello(const char* name)
{
    printf("Hello %s!\n", name);
}