Java Bytecode Subroutines - Cannot load return address
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13-03-2021 - |
题
I have been trying to write some Java bytecode and assemble it using Jasmin.
I am trying to get my head around subroutines, and am not sure why I obtain the following error message when running my program:
>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.
Here's the bytecode in test.j:
.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
I haven't had any problems with jumping to a single subroutine, but it seems as though something is going wrong when jumping to a subroutine from within a subroutine.
Any insight as to why this is failing would be much appreciated!
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