A JVM for the web. Bring back the applet!

Message me on Discord if you are interested in collaborating: forevermilk#0001

Style guide

Always use int64_t instead of long because Emscripten has sizeof(long) == 4. int can be assumed to be 32 bits.

Place all native functions in the corresponding folder in src/natives, and use the DECLARE_NATIVE macro to link them.

Common abbreviations:

• cf – classfile
• cp – constant pool
• bc – bytecode
• vm – virtual machine

Tasks

See GitHub issues

JITing to WebAssembly

• General method signature: bjvm_interpreter_result_t (*compiled)(bjvm_thread *thread, bjvm_cp_method *method, bjvm_stack_value *result, ... args)
• Generated on the fly for each argument type combination
• Longs are split into two ints to avoid overhead of creating bigints
• Method is responsible for setting up its own stack frame and in the case of de-opt or interruption, generating all interpreter stack frames
• Methods which are not compiled will have a generated implementation that delegates appropriately to the interpreter

Goals

• Full implementation of the JVM spec (including esoteric things like classfile verification)
• Java 17 support (starting with Java 8)
• Reasonably fast (geomean within factor of 10 of HotSpot in memory and CPU usage across benchmarks)
• JIT compilation to WebAssembly
• Interruptable execution
• Dynamic class loading
• Mild JNI compatibility

Non-goals

• Desktop JVM -- only useful for testing/debugging
• Swing, AWT, etc. compatibility
• Beautiful, elegant code (see QuickJS for that)

Useful

clang-format -i test/*.cc src/**/*.c src/**/*.h