Two decades of smalltalk VM development: live VM development through simulation tools

Abstract

OpenSmalltalk-VM is a virtual machine (VM) for languages in the Smalltalk family (e.g. Squeak, Pharo) which is itself written in a subset of Smalltalk that can easily be translated to C. Development is done in Smalltalk, an activity we call "Simulation". The production VM is derived by translating the core VM code to C. As a result, two execution models coexist: simulation, where the Smalltalk code is executed on top of a Smalltalk VM, and production, where the same code is compiled to an executable through a C compiler. In this paper, we detail the VM simulation infrastructure and we report our experience developing and debugging the garbage collector and the just-in-time compiler (JIT) within it. Then, we discuss how we use the simulation infrastructure to perform analysis on the runtime, directing some design decisions we have made to tune VM performance. CCS Concepts • Software and its engineering → Runtime environments; Just-in-time compilers; Interpreters;

Cross-ISA testing of the Pharo VM: lessons learned while porting to ARMv8

“…First, Slang automatically introduces interpreter optimisations such as (a) the localisation of critical variables (frame pointer, instruction pointer) [15], (b) the inlining of bytecode cases inside the interpretation loop, or (c) threaded code [6]. Second, it allows us to simulate the Pharo VM just by executing it as normal Pharo code, avoiding expensive change-compile-test development cycles [17].…”

“…Several solutions have been proposed to aid in VM debugging tasks. Traditionally, VM simulation environments have appeared in Self [19], Smalltalk [12,17] and Metacircular VMs such as Maxine [20]. Complementary to simulation environments, multi-level debuggers [14,21] aid VM developers to switch views between the program-level and the implementation (VM)-level.…”

“…In this paper, we report on several lessons we learned while testing the Pharo VM, particularly while porting its Cogit JIT compiler to the AArch64 architecture. The Pharo VM presented already a high-level simulation environment that is very handy to simulate full executions and live program the VM [17] (See Section 2). We extended the preexisting simulation environment with a testing infrastructure that allows us to have fine-grained control of testing scenarios, making tests small, fast, reproducible, and cross-ISA (See Section 3).…”

Two decades of live coding and debugging of virtual machines through simulation

“…Two execution models are available, simulation, where the Slang code is executed on top of a Smalltalk VM, and production, where the same code is compiled to executable code through a C compiler. 4 Simulation is used to develop and debug the VM. It is possible to simulate the complete VM by executing the Slang code as Smalltalk, using an internal or external processor emulator to execute the native code generated by the the Just-in-Time (JIT) compiler.…”

“…The VM is actually written in a Smalltalk dialect, called Slang . Two execution models are available, simulation, where the Slang code is executed on top of a Smalltalk VM, and production, where the same code is compiled to executable code through a C compiler 4 …”