I changed the definition of at: for CompiledMethod to prevent it accessing bytes outside of the bytecodes part of a compiled method. �What's happening here is that a hash is being derived form the compiled method by looking at the pointers part of the compiled method (i.e. bytes < aMethod initialPC). �But it is wrong to try and derive a hash from these bytes. �Since the GC can move objects these bytes can change as the GC moves the literals a method references (unlike the bytes between: aMethod initialPC and: aMethod size).

Two conclusions:

The solution is to define CompiledMethod>hash such that it does not access bytes < initialPC. �The hash it is inheriting from ByteArray is fine for ByteArray but not at all OK for CompiledMethod.

The VM is revealing a latent bug, i.e. that on older VMs the system could be computing a variable hash, and hence result in not-found errors in certain circumstances, hence the VM is right to impose this stricter bounds checking.