In this work, we experiment with adapting live programming tools to make them safer for the development of Bee Smalltalk, they can work on systems which crashed or that are not fully working. We will show Metaphysics, a framework that combines mirrors and proxies to reify different message execution semantics, allowing execution of code by mixing behavior of a remote, possibly broken system with a local fully-working one. With Metaphysics we were able to create native code debugging and profiling tools.

1. debuggee
“nil” → 0x4010F8
debugger IDE
nil nil
PE/ELF Header
UndefinedObject
handle
Object
Smalltalk globals
Process
SmalltalkSystem
current process
Obj mirror
Cls mirror
UndefObj
stck mirror
stack
Only structural
access
How do we send
messages?
runtime
bridge
Cls mirror
Dict mirror
Smalltalk
Object

2. debugger IDE – messaging
proxy
sum?
runtime
[1,2,3]
handle
debuggee
[1,2,3]
using which
behavior?
[1,2,3]
execute remotely?
simulate
execution
locally?

3. debugger IDE – messaging subjects
subject
sum?
Trigger Mirage Direct
dispatch:#sum
[1,2,3]
runtime
[1,2,3]
handle
gate
debuggee
[1,2,3]

4. Trigger
subject
sum?
dispatch:#sum
[1,2,3]
dispatch: aMessage
| result |
self
saveContext;
passArguments;
pushReturnAddress;
setIP.
result := self run.
self restoreContext.
^result
[1,2,3]
handle
a Trigger

5. Mirage
dispatch: aMessage from: parentInterpreter
| method interpreter |
method := class compiledMethodFor: aMessage selector.
interpreter := SubjectInterpreter
on: aMessage receiver
with: aMessage arguments
for: method.
^interpreter
parent: parentInterpreter;
evaluate: method parseTree
[1,2,3]
handle
subject
sum?
dispatch:#sum
[1,2,3]
Array
clas
s
a Mirage

6. Direct
dispatch: aMessage from: parentInterpreter
| receiver method interpreter |
receiver := aMessage receiver.
method := handle runtime lookup: aMessage selector on: receiver.
interpreter := SubjectInterpreter
on: receiver
with: aMessage arguments
for: method.
^interpreter
parent: parentInterpreter;
evaluate: method parseTree
[1,2,3]
subject
sum?
aDirectGate
handle
dispatch:#sum
[1,2,3]