Where does the HotSpot JVM store interpreted bytecode?

0
votes

I've been wondering where interpreted byte-code of methods are stored internally in the JVM (specifically HotSpot x64). I know that methods that are JIT-ed are stored and can be accessed in the Method structure but I'm trying to understand where the JVM stores the byte-code converted to assembly instructions (I assume it stores them, otherwise there would be a lot of memory usage to interpret every invocation) as I wasn't able to find it in the internals source code.

1
javajvmjitjvm-hotspot

1 Answers

2
votes

Interpreting bytecode is not as expensive as you would think. Why would the JVM spend time generating machine code for code that runs once? Best to wait until a certain method or block reaches the JIT threshold and only then spend time enabling the tracing JIT.

The src/share/vm/interpreter subdirectory seems to be what you're after:

  • bytecodeInterpreter.cpp implements the actual stack machine;
  • bytecodes.cpp defines the shape and attributes of each opcode.
  • bytecodes.h declares all bytecodes.
  • templateTable.cpp contains machinery to map JVM opcodes to assembly.
  • cpu/*/vm/templateTable*.cpp contains the actual code to generate assembly snippets for the given CPU.