Re: [Pharo-dev] Sista alternate bytecodes + Java Bytecode ?
That question should be asked on vm-dev.
Just a detail, multibytecode set support is prior to the Sista implementation, it was used for example in the context of Newspeak (Squeak and Newspeak bytecodes supported together). Sista uses that feature, which makes it look like new in the Pharo community since afaik no one used it before in the context of Pharo.
Then yes it is feasible to have the VM process Java bytecode, but it's humongous work. On the top my head, we would need to support typed bytecodes for Numbers and exceptions at the bytecode level (which in itself is month of work, imagine raising an exception from Java/ST and catch it from the other runtime, with multiple ensure/try finally in between)
Note that supporting the Java bytecode is far from enough to be able to run Java code (We also need core Java libraries support at least, including exceptions/stack reification model that should be able to interact with each other)
You can have a look at Smalltalk/X where the VM can run Java, C and Smalltalk.