Java 字节码子例程 - 无法加载返回地址

Question

我一直在尝试编写一些 Java 字节码并使用 Jasmin 对其进行汇编。

我正在尝试了解子例程，并且不确定为什么在运行程序时收到以下错误消息：

>java -jar jasmin.jar test.j
Generated: test.class

>java test
Exception in thread "main" java.lang.VerifyError: (class: test,
method: main signature: ([Ljava/lang/String;)V)
Cannot load return address from register 0
Could not find the main class: test. Program will exit.

这是 test.j 中的字节码：

.class public test
.super java/lang/Object
.method public static main([Ljava/lang/String;)V
.limit stack 6
.limit locals 5

jsr a     ;Jump to subroutine 'a', pushing return address on operand stack
return    ;Exit the program

a:
astore_0  ;Store the return address in variable 0
aload_0   ;Save the address onto the stack as address will be overwritten in 'b'
jsr b     ;Jump to subroutine 'b', pushing return address on operand stack
astore_0  ;Store the address that was on the stack back into variable 0
ret 0     ;Return to just after "jsr a"

b:
astore_0  ;Store return address in variable 0
ret 0     ;Return to address stored in 0 (ie back to just after the jump in 'a')

.end method

我在跳转到单个子例程时没有遇到任何问题，但它从子例程内跳转到子例程时似乎出现了问题。

任何关于为什么失败的见解将不胜感激！

Answer 1

您无法将地址类型值加载到任何寄存器中，您只能存储它，然后 ret 指令可以从那里检索它。

Java 虚拟机规范：

• ret
• jsr