jasmin hacking and verify error

Question

I'm playing with jasmin and I try to launch my .class file, which is supposed to perform simple string concatenation. My jasmin source looks like this:

.class public default_class
.super java/lang/Object
.method public static main([Ljava/lang/String;)V
.limit locals 1
.limit stack 1
invokestatic main_65428301()I
return
.end method
.method public static main_65428301()I
.limit locals 1
.limit stack 100
new java/lang/String
dup
ldc "foo"
invokestatic java/lang/String.valueOf(Ljava/lang/Object;)Ljava/lang/String;
invokespecial java/lang/StringBuilder(Ljava/lang/String;)V
ldc "bar"
invokevirtual java/lang/StringBuilder.append(Ljava/lang/String;)Ljava/lang/StringBuilder;
invokevirtual java/lang/String.toString()V
astore_0
iconst_0
ireturn
.end method

Now I'm able to run java -jar jasmin.jar and I get default_class.class. However, when I try to launch it like java default_class I get an error:

Exception in thread "main" java.lang.VerifyError: (class: default_class, method: main_65428301 signature: ()I) Illegal use of nonvirtual function call

What should I change in my assembly to get this to work?

score 1 · Accepted Answer · answered Jan 05 '13 at 14:05

1

In JVM, to create the object you have to first use new instruction and then call <init> method (constructor). You do not create new StringBuilder and call the wrong constructor name (should be java/lang/StringBuilder/<init>(Ljava/lang/String;)V).

I also see no reason to do:

new java/lang/String
dup

or

invokestatic java/lang/String.valueOf(Ljava/lang/Object;)Ljava/lang/String;

answered Jan 05 '13 at 14:05

zch

14,931
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49

I tried to mimic what eclipse do in similar situation, but thanks for pointing this out. Anyway I'd like to know what's wrong with invocation of my second main-like method, because that's what error message suggest – k_wisniewski Jan 05 '13 at 14:19
1

@k_wisniewski, In my opinion it refers to `invokespecial java/lang/StringBuilder(Ljava/lang/String;)V`, which is inside `(class: default_class, method: main_65428301 signature: ()I)` – zch Jan 05 '13 at 14:24
OK, I got rid of this problem now – k_wisniewski Jan 06 '13 at 12:01

score 0 · Answer 2 · answered Jan 05 '13 at 14:06

0

"The new instruction does not completely create a new instance; instance initialization is not completed until an instance initialization method has been invoked on the uninitialized instance."

answered Jan 05 '13 at 14:06

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jasmin hacking and verify error

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