常量入栈指令
Java程序的反编译工具已经十分成熟了，相对于x86平台更底层指令的反编译技术来说，面向VM的 bytecode更容易反编译。这主要是因为：
- 字节码含有更为丰富的数据类型信息。
- JVM内存模型更严格，因此字节码分析起来更为有章可循。
- Java编译器不做任何优化工作（而 JVM JIT在运行时会做优化工作），因此在反编译字节码之后，我们基本可以直接理解Java类文件里的原始指令。
反编译有什么用途呢？
- 无需重新编译反汇编的结果，而能给类文件做应急补丁。
- 分析混淆代码。
- 需要编写自己的代码混淆器。
- 创建面向JVM的、类似编译程序的代码生成工具（类似 Scala，Cloture等等）。
- 破解研究
开启Java逆向学习系列笔记，参考网上各大神的分享，有不对的请指正。
常量入栈指令有iconst、bipush、sipush、ldc、ldc2_w分别对应不同的使用场景
八大基本类型场景表
| 常量类型 |
常量范围 |
指令 |
| 整型int |
-1~5 |
iconst_0~ iconst_5 iconst_m1 |
| -128~127 |
bipush |
|
| -32768~32767 |
sipush |
|
| -2147483648~2147483647 |
#2 = Integer 12345678 0: ldc #2 // int 12345678 |
|
| 布尔型boolean |
true |
iconst_1 |
| false |
iconst_0 |
|
| 短整型short |
-1~5 |
iconst_0~ iconst_5 iconst_m1 |
| -128~127 |
bipush |
|
| -32768~32767 |
sipush |
|
| 字符型char |
\u0000~\u0005 |
iconst_0~ iconst_5 |
| \u0000~\u00FF |
bipush |
|
| \u0000~\uFFFF |
sipush |
|
| 字节型byte |
-1~5 |
iconst_0~ iconst_5 iconst_m1 |
| -128~127 |
bipush |
|
| 长整型long |
-2^63~2^63-1 |
#2 = Long 1234567890123456789l ldc2_w #2 // long 1234567890123456789l |
| 浮点型double |
8字节 |
#2 = Double 123.456d ldc2_w #2 // double 123.456d |
| 浮点型float |
4字节 |
#2 = Float 123.456f ldc #2 // float 123.456f |
指令场景表
| 指令 |
使用场景 |
| iconst |
int,short,byte,int(char a)数值在-1~5之间，boolean类型，注意不包括long |
| bipush |
int,short,byte,int(char a)数值在-128~127之间，注意不包括long，范围内的值在iconst之内的优先用iconst |
| sipush |
int,short,int(char a)数值在-32768~32767之间，boolean类型，注意不包括long，范围内的值在bipush之内的优先用bipush |
| ldc |
int的数值-2147483648~2147483647之间（范围内的值在sipush之内的优先用sipush），float类型 |
| ldc2_w |
long类型，double类型 |
以下是简单的例子
整型常量0的例子iconst
public class ret
{
public static int main(String[] args)
{
return 0;
}
}编译
javac ret.javaJava标准反编译
javap -c -verbose ret.class...
major version: 52
...
public static int main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)I
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=1, locals=1, args_size=1
0: iconst_0
1: ireturn
LineNumberTable:
line 5: 0注意其中的0: iconst_0即可
整型常量123的例子bipush
public class ret
{
public static int main(String[] args)
{
return 123;
}
}反编译
...
major version: 52
...
public static int main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)I
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=1, locals=1, args_size=1
0: bipush 123
2: ireturn
LineNumberTable:
line 5: 0注意其中的0: bipush 123
整型常量1234的例子sipush
public class ret
{
public static int main(String[] args)
{
return 1234;
}
}反编译
...
major version: 52
...
public static int main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)I
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=1, locals=1, args_size=1
0: sipush 1234
3: ireturn
LineNumberTable:
line 5: 0注意其中的 0: sipush 1234
整型常量12345678的例子ldc
public class ret
{
public static int main(String[] args)
{
return 12345678;
}
}反编译
...
major version: 52
...
#2 = Integer 12345678
...
public static int main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)I
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=1, locals=1, args_size=1
0: ldc #2 // int 12345678
2: ireturn
LineNumberTable:
line 5: 0
布尔型true例子iconst
public class ret
{
public static boolean main(String[] args)
{
return true;
}
}反编译
...
major version: 52
...
public static boolean main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)Z
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=1, locals=1, args_size=1
0: iconst_1
1: ireturn
LineNumberTable:
line 5: 0注意0: iconst_1即ture用常量1表示
短整型short例子
public class ret
{
public static short main(String[] args)
{
return 1234;
}
}反编译
...
major version: 52
...
public static short main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)S
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=1, locals=1, args_size=1
0: sipush 1234
3: ireturn
LineNumberTable:
line 5: 0注意0: sipush 1234
字符型A例子
public class ret
{
public static char main(String[] args)
{
return 'A';
}
}反编译
...
major version: 52
...
public static char main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)C
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=1, locals=1, args_size=1
0: bipush 65
2: ireturn
LineNumberTable:
line 5: 0注意0: bipush 65
字符型中例子
public class ret
{
public static char main(String[] args)
{
return '中';
}
}反编译
...
major version: 52
...
public static char main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)C
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=1, locals=1, args_size=1
0: sipush 20013
3: ireturn
LineNumberTable:
line 5: 0注意0: sipush 20013
byte类型123列子
public class ret
{
public static byte main(String[] args)
{
return 123;
}
}反编译
...
major version: 52
...
public static byte main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)B
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=1, locals=1, args_size=1
0: bipush 123
2: ireturn
LineNumberTable:
line 5: 0注意 0: bipush 123
long类型1234567890123456789L例子
public class ret
{
public static long main(String[] args)
{
return 1234567890123456789l;
}
}反编译
...
major version: 52
...
#2 = Long 1234567890123456789l
...
public static long main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)J
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=2, locals=1, args_size=1
0: ldc2_w #2 // long 1234567890123456789l
3: lreturn
LineNumberTable:
line 5: 0注意0: ldc2_w #2 // long 1234567890123456789l
浮点类型123.456d的例子
public class ret
{
public static double main(String[] args)
{
return 123.456d;
}
}反编译
...
major version: 52
...
#2 = Double 123.456d
...
public static double main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)D
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=2, locals=1, args_size=1
0: ldc2_w #2 // double 123.456d
3: dreturn
LineNumberTable:
line 5: 0注意0: ldc2_w #2 // double 123.456d
浮点类型123.456f的例子
public class ret
{
public static float main(String[] args)
{
return 123.456f;
}
}反编译
...
major version: 52
...
#2 = Float 123.456f
...
public static float main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)F
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=1, locals=1, args_size=1
0: ldc #2 // float 123.456f
2: freturn
LineNumberTable:
line 5: 0注意0: ldc #2 // float 123.456f
本文参考：逆向工程权威指南.下册.pdf 和http://blog.51cto.com/7317859/2105269