Hi,
I have been going over the internals of Kaffe's execution code,
specifically the way the interpreter's internal stack operates. What
I understand so far, Kaffe is a stack based interpreter. The stack is
a stack of 'slots' (defined in slots.h). A slot is big enough to
store the largest data type in Java. We push and pop this data
to/from the stack. Easy enough, what I don't understand is why we
treat doubles and longs differently.
Extract from kaffe.def
define_insn_alias(LCONST_1)
{
/*
* ... -> ..., 0, [0 .. 1]
*/
trace_jcode ("lconst %d\n", getopcode() - LCONST_0);
push(2);
move_long_const(stack_long(0), getopcode() - LCONST_0);
}
The push(2) allocates 2 slots on the stack, and then we move the local
constant to the top of the stack. Easy enough. What I don't
understand is since a slot is big enough to hold the long, why are we
allocating 2 slots? Since we only operate on a slot and not 2
concatenated slots, this would imply that we are putting a hole in the
stack when ever we have a long or double operand. Is there something
that I am missing on this?
Thanks
Michael
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