class文件
查看16进制：
public class ByteCode {
private int m;
public int inc() {
return m + 1;
}
}
javac ByteCode.java
vim ByteCode.class
:%!xxd
00000000: cafe babe 0000 0034 0013 0a00 0400 0f09 .......4........
00000010: 0003 0010 0700 1107 0012 0100 016d 0100 .............m..
00000020: 0149 0100 063c 696e 6974 3e01 0003 2829 .I...<init>...()
00000030: 5601 0004 436f 6465 0100 0f4c 696e 654e V...Code...LineN
00000040: 756d 6265 7254 6162 6c65 0100 0369 6e63 umberTable...inc
00000050: 0100 0328 2949 0100 0a53 6f75 7263 6546 ...()I...SourceF
00000060: 696c 6501 000d 4279 7465 436f 6465 2e6a ile...ByteCode.j
00000070: 6176 610c 0007 0008 0c00 0500 0601 001b ava.............
00000080: 636f 6d2f 6578 616d 706c 652f 6465 6d6f com/example/demo
各字节含义：按顺序（u1 u2 u4 u8分别代表1 2 4 8字节，其他是表类型）
计算得出 更直观展示各字节含义：
javap -verbose ByteCode.class
Classfile xxxx/ByteCode.class
Last modified 2018-9-30; size 292 bytes
MD5 checksum 775471577fc46c33efff4361644724aa
Compiled from "ByteCode.java"
public class com.example.demoms.ByteCode
minor version: 0
major version: 52
flags: ACC_PUBLIC, ACC_SUPER
constant pool:
#1 = Methodref #4.#15 // java/lang/Object."<init>":()V
#2 = fieldref #3.#16 // com/example/demoms/ByteCode.m:I
#3 = Class #17 // com/example/demoms/ByteCode
#4 = Class #18 // java/lang/Object
#5 = Utf8 m
#6 = Utf8 I
#7 = Utf8 <init>
#8 = Utf8 ()V
#9 = Utf8 Code
#10 = Utf8 LineNumberTable
#11 = Utf8 inc
#12 = Utf8 ()I
#13 = Utf8 SourceFile
#14 = Utf8 ByteCode.java
#15 = NameAndType #7:#8 // "<init>":()V
#16 = NameAndType #5:#6 // m:I
#17 = Utf8 com/example/demoms/ByteCode
#18 = Utf8 java/lang/Object
{
public com.example.demoms.ByteCode();
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 9: 0
public int inc();
descriptor: ()I
flags: ACC_PUBLIC
Code:
stack=2, locals=1, args_size=1
0: aload_0
1: getfield #2 // Field m:I
4: iconst_1
5: iadd
6: ireturn
LineNumberTable:
line 14: 0
}
SourceFile: "ByteCode.java"
查看字节码指令：(jvm指令)
javap -c ByteCode.class
public class com.example.demoms.ByteCode {
public com.example.demoms.ByteCode();
Code:
0: aload_0
1: invokespecial #1 // Method java/lang/Object."<init>":()V
4: return
public int inc();
Code:
0: aload_0
1: getfield #2 // Field m:I
4: iconst_1
5: iadd
6: ireturn
}
查看反汇编指令：
/**
*JVM参数输出反汇编
* -XX:+UnlockDiagnosticVMOptions -XX:+printAssembly
*/
public class ByteCode {
private int m;
public int inc() {
return m + 1;
}
public static void main(String[] args) {
}
}
反汇编输出的代码有点多…部分如下：
Loaded disassembler from hsdis-AMD64.dylib
Decoding compiled method 0x000000010e198610:
Code:
[Disassembling for mach='i386:x86-64']
[Entry Point]
[constants]
# {method} {0x00000001070e6480} '<init>' '()V' in 'java/lang/Object'
# [sp+0x20] (sp of caller)
0x000000010e198760: mov 0x8(%rsi),%r10d
0x000000010e198764: shl $0x3,%r10
0x000000010e198768: cmp %r10,%rax
0x000000010e19876b: jne 0x000000010e0d8e60 ; {runtime_call}
0x000000010e198771: data32 xchg %ax,%ax
0x000000010e198774: nopl 0x0(%rax,%rax,1)
0x000000010e19877c: data32 data32 xchg %ax,%ax
[Verified Entry Point]
0x000000010e198780: mov %eax,-0x14000(%rsp)
0x000000010e198787: push %rbp
0x000000010e198788: sub $0x10,%rsp ;*synchronization entry
; - java.lang.Object::<init>@-1 (line 37)
0x000000010e19878c: mov 0x8(%rsi),%r11d
0x000000010e198790: movabs $0x0,%r10
0x000000010e19879a: lea (%r10,%r11,8),%r10
0x000000010e19879e: mov $0x40000000,%r8d
0x000000010e1987a4: test %r8d,0x9c(%r10)
0x000000010e1987ab: je 0x000000010e1987b8 ;*return
; - java.lang.Object::<init>@0 (line 37)
0x000000010e1987ad: mov %rsi,%rbp
0x000000010e1987b0: data32 xchg %ax,%ax
0x000000010e1987b3: callq 0x000000010e104960 ; OopMap{rbp=Oop off=88}
;*return
; - java.lang.Object::<init>@0 (line 37)
; {runtime_call}
0x000000010e1987b8: add $0x10,%rsp
0x000000010e1987bc: pop %rbp
0x000000010e1987bd: test %eax,-0xd7a47c3(%rip) # 0x00000001009f4000
; {poll_return}
0x000000010e1987c3: retq ;*return
; - java.lang.Object::<init>@0 (line 37)
0x000000010e1987c4: mov %rax,%rsi
0x000000010e1987c7: add $0x10,%rsp
0x000000010e1987cb: pop %rbp
0x000000010e1987cc: jmpq 0x000000010e104760 ; {runtime_call}
0x000000010e1987d1: hlt
0x000000010e1987d2: hlt
0x000000010e1987d3: hlt
0x000000010e1987d4: hlt
0x000000010e1987d5: hlt
0x000000010e1987d6: hlt
0x000000010e1987d7: hlt
0x000000010e1987d8: hlt
0x000000010e1987d9: hlt
0x000000010e1987da: hlt
0x000000010e1987db: hlt
0x000000010e1987dc: hlt
0x000000010e1987dd: hlt
0x000000010e1987de: hlt
0x000000010e1987df: hlt
[Exception handler]
[Stub Code]
0x000000010e1987e0: jmpq 0x000000010e1017e0 ; {no_reloc}
[Deopt Handler Code]
0x000000010e1987e5: callq 0x000000010e1987ea
0x000000010e1987ea: subq $0x5,(%rsp)
0x000000010e1987ef: jmpq 0x000000010e0da500 ; {runtime_call}
0x000000010e1987f4: hlt
0x000000010e1987f5: hlt
0x000000010e1987f6: hlt
0x000000010e1987f7: hlt
Decoding compiled method 0x000000010e1988d0:
Code:
[Entry Point]
[Verified Entry Point]
当然也可以使用一些其他的反编译插件…
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