Calling an assembly function from Java

readme.txt

Assuming a 64 bit system.

Translate java part:
markus@utopic:/tmp$ javac AsmTest.java 

Translate assembly part:
markus@utopic:/tmp$ nasm -f elf64 -o addThem.o addThem.asm 

Create a shared object:
markus@utopic:/tmp$ gcc -shared -o libaddThem.so addThem.o

Run the java program:
markus@utopic:/tmp$ java -Djava.library.path=. AsmTest
OpenJDK 64-Bit Server VM warning: You have loaded library /tmp/libaddThem.so which might have disabled stack guard. The VM will try to fix the stack guard now.
It's highly recommended that you fix the library with 'execstack -c <libfile>', or link it with '-z noexecstack'.
Result: 9
markus@utopic:/tmp$ 

addThem.asm

[BITS 64]

GLOBAL Java_AsmTest_addThem
Java_AsmTest_addThem:
        mov rax, rdx
        add rax, rcx

        ret

AsmTest.java

public class AsmTest {
        public static native int addThem(int a, int b);

        static {
                // Looks for libaddThem.so or addThem.dll, depending on the OS
                System.loadLibrary("addThem");
        }

        public static void main(String[] args) {
                int result = addThem(4, 5);

                System.out.println("Result: " + result);
        }
}