On Mar 31, 2017, at 8:57 AM, Remi Forax <fo...@univ-mlv.fr> wrote: > > I've some trouble to see how value types are laid on stack (conceptually, not > necessary the real implementation). > > First, i may be wrong but it seems that vload do not reference the > corresponding Q-type, so i wonder how the verifier knows that it can then > access to component of the value type. > Then, it seems that value type use one slot on stack, so the components (and > the boxed reference if it exists) has to be stored somewhere but there is no > corresponding max value type buffer size.
In the interpreter value types all share a common _carrier type_ which includes metadata about the size and type of the value being stored, plus a pointer to the actual storage. The actual storage may be on the heap, or maybe not. We are prototyping with thread-local arenas for the non-heap case. There are also ways to store value payloads in the stack frame, but in that case there is a special handshake when you want to return a value from a method call. From the verifier's point of view, there isn't much difference between the various Q-types. We will probably track classes of Q-types, mainly to simplify vgetfield operations. — John
