Jazelle - Application Binary Interface (ABI)

Application Binary Interface (ABI)

The Jazelle state relies on an agreed calling convention between the JVM and the Jazelle hardware state. This application binary interface is not published by ARM, rendering Jazelle an undocumented feature for most users and Free Software JVMs.

The entire VM state is held within normal ARM registers, allowing compatibility with existing operating systems and interrupt handlers unmodified. Restarting a bytecode (such as following a return from interrupt) will re-execute the complete sequence of related ARM instructions.

Specific registers are designated to hold the most important parts of the JVM state: registers r0-r3 hold an alias of the top of the Java stack, r4 holds Java local operand zero (pointer to *this) and r6 contains the Java stack pointer.

Jazelle reuses the existing Program Counter register r15. A pointer to the next bytecode goes in r14, so the use of the PC is not generally user-visible except during debugging.