Reverse Engineering for Beginners

CHAPTER 54. JAVA CHAPTER 54. JAVA

7: iload_1

8: iload_2

9: invokestatic #2 // Method max:(II)I

12: istore_3

13: iload_1

14: iload_2

15: invokestatic #3 // Method min:(II)I

18: istore 4

20: getstatic #4 // Field java/lang/System.out:Ljava/io/⤦

ÇPrintStream;

23: iload 4

25: invokevirtual #5 // Method java/io/PrintStream.println:(I)V

28: getstatic #4 // Field java/lang/System.out:Ljava/io/⤦

ÇPrintStream;

31: iload_3

32: invokevirtual #5 // Method java/io/PrintStream.println:(I)V

35: return

Arguments are passed to the other function in the stack, and the return value is left onTOS.

54.10Bitfields

All bit-wise operations work just like in any otherISA:

public static int set (int a, int b)

{

return a | 1<<b;

}

public static int clear (int a, int b)

{

return a & (~(1<<b));

}

public static int set(int, int);

flags: ACC_PUBLIC, ACC_STATIC

Code:

stack=3, locals=2, args_size=2

0: iload_0

1: iconst_1

2: iload_1

3: ishl

4: ior

5: ireturn

public static int clear(int, int);

flags: ACC_PUBLIC, ACC_STATIC

Code:

stack=3, locals=2, args_size=2

0: iload_0

1: iconst_1

2: iload_1

3: ishl

4: iconst_m1

5: ixor

6: iand

7: ireturn

iconst_m1loads− 1 in the stack, it’s the same as the0xFFFFFFFFnumber. XORing with0xFFFFFFFFhas the same
effect of inverting all bits (A.6.2 on page 889).

Let’s extend all data types to 64-bitlong:

public static long lset (long a, int b)

{

return a | 1<<b;

}