Hi Ronie,
From my understanding, following code cannot work in x64 because registers
are overwritten while marshalling arguments:
generateLowcodeObjectTrampolines ... snip ... ceInstantiateClassIndexableSizeTrampoline := cogit genTrampolineFor: #instantiateClass:indexableSize: called: 'ceInstantiateClassIndexableSizeTrampoline' arg: ReceiverResultReg arg: Arg0Reg result: TempReg.
The first arg ReceiverResultReg (RDX) will overwrite Arg0Reg (RDI) before Arg0Reg is copied to Arg1Reg (RSI)... See genMarshallNArgs:arg:arg:arg:arg: and carefully read the comment for the x64 flavour, it's scary ;)
Cheers