《re：从零开始的java逆向基础》#3方法（函数）

Lightcolour · 发表于 2019-9-20 16:05

先定义一个方法

public class Main {

publicstatic double getNumber() {

returnMath.random()/2;

}

反编译

Constant pool:

#1 = Methodref #6.#15 //java/lang/Object."<init>":()V

#2 = Methodref #16.#17 //java/lang/Math.random:()D

#3 = Double 2.0d

#5 = Class #18 // Main

#6 = Class #19 // java/lang/Object

#7 = Utf8 <init>

#8 = Utf8 ()V

#9 = Utf8 Code

#10 = Utf8 LineNumberTable

#11 = Utf8 getNumber

#12 = Utf8 ()D

#13 = Utf8 SourceFile

#14 = Utf8 Main.java

#15 = NameAndType #7:#8 //"<init>":()V

#16 = Class #20 // java/lang/Math

#17 = NameAndType #21:#12 // random:()D

#18 = Utf8 Main

#19 = Utf8 java/lang/Object

#20 = Utf8 java/lang/Math

#21 = Utf8 random

{

public Main();

descriptor: ()V

flags: ACC_PUBLIC

Code:

stack=1, locals=1, args_size=1

0: aload_0

1: invokespecial #1 // Methodjava/lang/Object."<init>":()V

4: return

LineNumberTable:

line 1: 0

public static double getNumber();

descriptor: ()D

flags: ACC_PUBLIC, ACC_STATIC

Code:

stack=4, locals=0, args_size=0

0: invokestatic #2 // Method java/lang/Math.random:()D

3: ldc2_w #3 // double 2.0d

6: ddiv

7: dreturn

LineNumberTable:

line 3: 0

}

SourceFile: "Main.java"

invokestatic #2 调用常量#2定义的函数也就是说调用了这个方法得到了一个随机数

函数名定义再常量池Methodref中定义类方法返回

2 = Methodref #16.#17 //java/lang/Math.random:()D

也就是说 #2 是#16#17 拼接成的

#16定义了类名Method java/lang/Math #17定义了方法 random返回类型()D

#17 = NameAndType #21:#12 // random:()D

也就是说 #17 是#21#12 拼接成的

#21 定义了random 方法

#12 返回类型()D

()括号内没有东西表示没参数

我们再看看返回一个String的例子

public class Main {

public staticvoid main(String[] args) {

System.out.println("Lightcolour");

}

反编译

Lastmodified 2019-9-20; size 413 bytes

MD5checksum 8e45b6aafc1404a9c015f8c0f03e385c

Compiled from "Main.java"

public class Main

minorversion: 0

majorversion: 52

flags: ACC_PUBLIC, ACC_SUPER

Constant pool:

#1 =Methodref #6.#15 //java/lang/Object."<init>":()V

#2 =Fieldref #16.#17 //java/lang/System.out:Ljava/io/PrintStream;

#3 =String #18 // Lightcolour

#4 =Methodref #19.#20 //java/io/PrintStream.println:(Ljava/lang/String;)V

#5 =Class #21 // Main

#6 =Class #22 // java/lang/Object

#7 =Utf8 <init>

#8 =Utf8 ()V

#9 =Utf8 Code

#10 =Utf8 LineNumberTable

#11 =Utf8 main

#12 =Utf8 ([Ljava/lang/String;)V

#13 =Utf8 SourceFile

#14 =Utf8 Main.java

#15 =NameAndType #7:#8 // "<init>":()V

#16 =Class #23 // java/lang/System

#17 =NameAndType #24:#25 // out:Ljava/io/PrintStream;

#18 =Utf8 Lightcolour

#19 =Class #26 // java/io/PrintStream

#20 =NameAndType #27:#28 // println:(Ljava/lang/String;)V

#21 =Utf8 Main

#22 =Utf8 java/lang/Object

#23 =Utf8 java/lang/System

#24 =Utf8 out

#25 =Utf8 Ljava/io/PrintStream;

#26 =Utf8 java/io/PrintStream

#27 =Utf8 println

#28 =Utf8 (Ljava/lang/String;)V

{

public Main();

descriptor: ()V

flags: ACC_PUBLIC

Code:

stack=1, locals=1, args_size=1

0: aload_0

1: invokespecial #1 // Method java/lang/Object."<init>":()V

4: return

LineNumberTable:

line 1: 0

public static void main(java.lang.String[]);

descriptor: ([Ljava/lang/String;)V

flags: ACC_PUBLIC, ACC_STATIC

Code:

stack=2, locals=1, args_size=1

0: getstatic #2 // Fieldjava/lang/System.out:Ljava/io/PrintStream;

3: ldc #3 // String Lightcolour

5: invokevirtual #4 // Methodjava/io/PrintStream.println:(Ljava/lang/String;)V

8: return

LineNumberTable:

line 3: 0

line 4: 8

}

getstatic #2获取System.out的引用入栈

ldc将字符串“Lightcolour” 入栈

invokevirtual 调用println方法这里会进行2个操作 1、将字符串Lightcolour出栈传入(Ljava/lang/String;)V 2、将System.out 出栈传入java/io/PrintStream.println

再看beep方法

public class Main {

public staticvoid main(String[] args) {

java.awt.Toolkit.getDefaultToolkit().beep();

}

反编译

Lastmodified 2019-9-20; size 355 bytes

MD5checksum 7c26b26edfdde5f4bb8410a0f05bc289

Compiled from "Main.java"

public class Main

minorversion: 0

majorversion: 52

flags: ACC_PUBLIC, ACC_SUPER

Constant pool:

#1 =Methodref #5.#14 //java/lang/Object."<init>":()V

#2 =Methodref #15.#16 //java/awt/Toolkit.getDefaultToolkit:()Ljava/awt/Toolkit;

#3 =Methodref #15.#17 // java/awt/Toolkit.beep:()V

#4 =Class #18 // Main

#5 =Class #19 // java/lang/Object

#6 =Utf8 <init>

#7 =Utf8 ()V

#8 =Utf8 Code

#9 =Utf8 LineNumberTable

#10 =Utf8 main

#11 =Utf8 ([Ljava/lang/String;)V

#12 =Utf8 SourceFile

#13 =Utf8 Main.java

#14 =NameAndType #6:#7 // "<init>":()V

#15 =Class #20 // java/awt/Toolkit

#16 =NameAndType #21:#22 //getDefaultToolkit:()Ljava/awt/Toolkit;

#17 =NameAndType #23:#7 // beep:()V

#18 =Utf8 Main

#19 =Utf8 java/lang/Object

#20 =Utf8 java/awt/Toolkit

#21 =Utf8 getDefaultToolkit

#22 =Utf8 ()Ljava/awt/Toolkit;

#23 =Utf8 beep

{

public Main();

descriptor: ()V

flags:ACC_PUBLIC

Code:

stack=1, locals=1, args_size=1

0: aload_0

1: invokespecial #1 //Method java/lang/Object."<init>":()V

4: return

LineNumberTable:

line 1: 0

public static void main(java.lang.String[]);

descriptor: ([Ljava/lang/String;)V

flags: ACC_PUBLIC, ACC_STATIC

Code:

stack=1, locals=1, args_size=1

0: invokestatic #2// Methodjava/awt/Toolkit.getDefaultToolkit:()Ljava/awt/Toolkit;

3: invokevirtual #3 // Methodjava/awt/Toolkit.beep:()V

6: return

LineNumberTable:

line 3: 0

line 4: 6

}

invokestatic #2 调用java.awt.Toolkit.getDefaultToolkit()方法

invokevirtual #3 调用beep()函数

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50311048 · 发表于 2019-9-20 23:29

你将受到所有人的崇拜！

豆0o0豆 · 发表于 2021-12-7 22:10

感谢分享呀

豆0o0豆 · 发表于 2021-12-19 00:04

感谢分享 (￣▽￣)"

bnjzzheng · 发表于 2022-1-11 21:59

多谢分享。多谢

xujinwen · 发表于 2022-1-12 20:11

谢谢大佬分享

越宝 · 发表于 2022-1-13 10:09

谢谢大佬！

hetao8003200 · 发表于 2022-1-13 11:09

感谢楼主分享

6378895 · 发表于 2022-1-13 12:22

越宝 · 发表于 2022-1-13 18:08

谢谢大佬！

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