Re: [BCEL-info]setting of maxstack in helloify.java

[Enver H. <eh...@in...>]

On Sat, 27 Jul 2002, Aarti Thorat wrote:
>
> Hence i changed it to 2 * no of times method call inserted, it worked
> fine. But the lower limit for which the classfile works fine is 3.
>
> I am a little confused, as to what exactly the max stack depends on, the
> number of arguments taken by the method or the code length of the method.
> Can any one please throw some light on this issue ?

The JVM works stack-based, i.e. many instructions auch as IADD expect
arguments on the stack and/or put arguments on the stack. MaxStack is all
about the argument stack; arguments meaning arguments to the instructions,
not the method parameters!

This is the stack size in question here. For example, IADD does

 push(pop() + pop());

Usually, one would implement "2+3+4" as

 iconst_2 ; push "2" onto stack
 iconst_3
 iadd
 iconst_4
 iadd

You have at most two stack slots used here (an int uses one slot);
so maxStack = 2.

but you could also

 iconst_2
 iconst_3
 iconst_4
 iadd
 iadd

Here, there are three stack slots used at one time, so maxStack = 3.
Hope the example helps.

If unsure, just increase the maxStack. The calculation in Method.java
also sometimes is a little off, better add some slots to be on the
safe side.


Enver