The reference implementation of JSR 292 uses specially coded assembly stubs to perform common low-level calling sequence adapations. Some are not yet implemented, with their semantics being emulated (sometimes with limitations) by lots of little Java adapter classes. This leads to Java code complexity and limitations on argument counts.
The following still need to be implemented:
OP_PRIM_TO_REF : requires a stack frame if the boxing operation must block
OP_SPREAD_ARGS : requires a stack overflow check
OP_RICOCHET, OP_FLYBY : both require a stack frame to hold arguments for the final MH