| path | title |
|---|---|
/learnings/java_bytecode |
Learnings: Java: Bytecode |
JVM opcodes are 1 byte large. (200ish are used in Java9).
Statically typed
BIG ENDIAN
In general more CISC based architecture than RISC.
How does hotspot work? At a method (and sometimes loop) level. Because of this it will swap original pointer in the vtable of the object’s class structure. (See: Learning_Java_Memory_Hotspot_Object_Layout ).
invokevirtual bytecode must be emitted, even for "final" methods. (Aka: non virtualizable). Why? JavaSpec 13.4.7 says final -> virtual changes can’t break existing binaries. thus must assume lowest common denominator (and in this case invokespecial would invoke the old non-overridden implementation). - Optimizing Java
In general JITed things are moved into JIT "code cache"
OpenJDK code cache implementation: (they separate it into 3 parts)