[rvm-research] Question about LazyCompilationTrampoline in TIB

[Suriya S. <su...@cs...>]

Hi all,

I guess this is the first post this year. I wish everyone a happy new year.

I have a question about Trampolines in TIBs. In the code below, why is
callAddress an offset from tibAddress? Shouldn't callAddress be an offset
from address of (this.data[0])? Is there something special going on in the
layout of TIB objects in MemoryManager.newTIB()?

@NoInline
public void setVirtualMethod(int virtualMethodIndex, CodeArray code) {
  if (VM.VerifyAssertions) VM._assert(virtualMethodIndex >= 0);
  if (VM.runningVM && code == LazyCompilationTrampoline.instructions) {
    Address tibAddress = Magic.objectAsAddress(this);
    Address callAddress = tibAddress.plus(Offset.fromIntZeroExtend(lazyMethodInvokerTrampolineIndex() << LOG_BYTES_IN_ADDRESS));
    set(TIB_FIRST_VIRTUAL_METHOD_INDEX + virtualMethodIndex, callAddress);
  } ...


Thanks,
Suriya