这些说明适用于 Linux (Ubuntu 10.04.4 LTS)，但应该适用于您的操作系统。下载Oracle JDK 7u3并适当设置JAVA_HOME和PATH环境变量后，执行以下检查可用选项：
java -XX:+AggressiveOpts -XX:+UnlockDiagnosticVMOptions -XX:+UnlockExperimentalVMOptions -XX:+PrintFlagsFinal -version
您应该会看到UnlockDiagnosticVMOptions、CompileCommand 和PrintAssembly 选项可用。使用CompileCommand 选项也将启用PrintAssembly 选项。但是，您需要 PrintAssembly 的 HotSpot 反汇编插件才能工作；如果没有它，您可能会看到如下内容：
$ java -version
java version "1.7.0_03"
Java(TM) SE Runtime Environment (build 1.7.0_03-b04)
Java HotSpot(TM) Server VM (build 22.1-b02, mixed mode)
$ java -server -XX:+UnlockDiagnosticVMOptions '-XX:CompileCommand=print,*Main.main' Main
CompilerOracle: print *Main.main
Java HotSpot(TM) Server VM warning: printing of assembly code is enabled; turning on DebugNonSafepoints to gain additional output
Compiled method (c2) 68 1 % Main::main @ 4 (49 bytes)
total in heap [0xb3a97548,0xb3a979ec] = 1188
relocation [0xb3a97610,0xb3a97624] = 20
main code [0xb3a97640,0xb3a97840] = 512
stub code [0xb3a97840,0xb3a97850] = 16
oops [0xb3a97850,0xb3a97858] = 8
scopes data [0xb3a97858,0xb3a97898] = 64
scopes pcs [0xb3a97898,0xb3a979e8] = 336
dependencies [0xb3a979e8,0xb3a979ec] = 4
Could not load hsdis-i386.so; library not loadable; PrintAssembly is disabled
OopMapSet contains 1 OopMaps
要获得 HotSpot 反汇编插件，您需要构建它。查看 OpenJDK 7u2 源代码，hsdis plugin readme 说：
要将插件与 JVM 一起使用，您需要一个可以加载它的新版本。
如果你的 JVM 的产品模式不接受 -XX:+PrintAssembly，
您没有足够新的版本。
要构建这个项目，您 [需要] 一份 GNU binutils 的副本来构建。
理论上，这应该可以在 Windows 上构建，但可以正常工作
事实证明，Windows 上的 GNU 构建环境很困难。
我们在上面已经确认 Oracle JDK 7u3 支持PrintAssembly。我按照 hsdis 插件自述文件的说明，下载了 GNU binutils 2.22，将其放在 hsdis build/binutils 目录中并运行 make。这最终产生了以下错误：
hsdis.c:32:20: error: sysdep.h: No such file or directory
为了纠正这个问题，我使用以下补丁更改了 hsdis.c：
diff -r 6259c6d3bbb7 src/share/tools/hsdis/hsdis.c
--- a/src/share/tools/hsdis/hsdis.c Mon Dec 12 23:08:01 2011 -0800
+++ b/src/share/tools/hsdis/hsdis.c Thu Feb 23 09:26:37 2012 -0500
@@ -29,7 +29,7 @@
#include "hsdis.h"
-#include <sysdep.h>
+#include <errno.h>
#include <libiberty.h>
#include <bfd.h>
#include <dis-asm.h>
然后运行make 成功。现在只需将hsdis build 目录下的hsdis-i386.so 插件复制到Oracle JDK 7u3 jre/lib/i386 目录即可。
现在可以看到反汇编的编译代码了：
$ java -server -XX:+UnlockDiagnosticVMOptions '-XX:CompileCommand=print,*Main.main' Main
CompilerOracle: print *Main.main
Java HotSpot(TM) Server VM warning: printing of assembly code is enabled; turning on DebugNonSafepoints to gain additional output
Compiled method (c2) 68 1 % Main::main @ 4 (49 bytes)
total in heap [0xb3999548,0xb39999ec] = 1188
relocation [0xb3999610,0xb3999624] = 20
main code [0xb3999640,0xb3999840] = 512
stub code [0xb3999840,0xb3999850] = 16
oops [0xb3999850,0xb3999858] = 8
scopes data [0xb3999858,0xb3999898] = 64
scopes pcs [0xb3999898,0xb39999e8] = 336
dependencies [0xb39999e8,0xb39999ec] = 4
Loaded disassembler from [snip]/jdk1.7.0_03/jre/lib/i386/hsdis-i386.so
Decoding compiled method 0xb3999548:
Code:
[Disassembling for mach='i386']
[Entry Point]
[Verified Entry Point]
[Constants]
# {method} 'main' '([Ljava/lang/String;)V' in 'Main'
0xb3999640: call 0xb6ff8510 ; {runtime_call}
0xb3999645: data32 xchg %ax,%ax
0xb3999648: mov %eax,-0x3000(%esp)
0xb399964f: push %ebp
0xb3999650: sub $0x38,%esp
0xb3999656: mov %ecx,%esi
0xb3999658: mov 0x4(%esi),%ebp
0xb399965b: mov 0x8(%esi),%edi
0xb399965e: mov (%ecx),%esi
0xb3999660: mov %ecx,(%esp)
0xb3999663: call 0xb7078cf0 ;*iload_3
[snip]
0xb399983e: hlt
0xb399983f: hlt
[Exception Handler]
[Stub Code]
0xb3999840: jmp 0xb39981e0 ; {no_reloc}
[Deopt Handler Code]
0xb3999845: push $0xb3999845 ; {section_word}
0xb399984a: jmp 0xb397e220 ; {runtime_call}
0xb399984f: .byte 0x0
OopMapSet contains 1 OopMaps
#0
OopMap{off=468}
我用过的测试类是：
public class Main {
public static void main(final String[] args) {
long x = 0;
for (int i = 0; i < 1000000; i++) {
x += calculate(i);
}
System.out.println("x=" + x);
}
private static long calculate(final int i) {
return (long)i * (long)i;
}
}