unable to pop operand of empty stack

[Joanna Eriksson]

When running this: 

int main() {

  printBool(true);

  printBool(false);

  return 0 ;

}

void printBool(bool b) {

  if (b) {

  } else {

 }

}

We get:

.class public core013

.super java/lang/Object

.method public <init>()V

aload_0

invokenonvirtual java/lang/Object/<init>()V

return

.end method

.method public static main([Ljava/lang/String;)V

.limit locals 100

.limit stack 1000

invokestatic core013/main()I

return

.end method

.method public static main()I

.limit locals 100

.limit stack 1000

bipush 1

istore 1

invokestatic core013/printBool(B)V

bipush 0

istore 1

invokestatic core013/printBool(B)V

bipush 0

ireturn

.end method

.method public static printBool(B)V

.limit locals 100

.limit stack 1000

iload 1

ifeq IFFALSE0

goto IFTRUE0

IFFALSE0:

IFTRUE0:

return

.end method

This gives error Exception in thread "main" java.lang.VerifyError: (class: core013, method: main signature: ()I) Unable to pop operand off an empty stack.

Why?

[Linus Färnstrand]

Booleans don't have the signature char "B". It should be "Z"

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[Joanna Eriksson]

Unfortunately the error remains the same after replacing the B with Z. 

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[Aarne Ranta]

Hello Joanna,

In this part

bipush 1

istore 1

invokestatic core013/printBool(B)V

you are invoking printBool on an empty stack, because the pushed value 1 has been stored.

  Aarne.

[Irene Lobo Valbuena]

From what I see in your Jasmin code, there is nothing in the stack when the printBool call is reached since you push a value and then store it (the store will not only update your local memory, it also pops the stack when doing so). So it won't be possible to pop any operands off the stack.

[Joanna Eriksson]

Thanks, that solves the problem! However now we're instead getting

Exception in thread "main" java.lang.VerifyError: (class: core013, method: printBool signature: (Z)V) Accessing value from uninitialized register 1

Doesn't the istore put the value in register 1 so that printbool can use iload to get is?

[Aarne Ranta]

If it is the same code as before, you seem to be loading variable 1, but printBool has just one parameter b, which is stored in 0.

  Aarne.