The "Open On-Chip Debugger" provides JTAG/SWD access from GDB (or directly with TCL scripts) to processors with ARM and MIPS based cores.
See website for full list of supported targets.
Java classfile assembler/disassembler and interactive low-level editor
Java Classfile assembler/disassembler and low-level interactive editor. Allows viewing and manipulation of Java class data both manually and via scripts. Load in a class file, make changes, and then save the result.
JTools.Ruby is easy way to access Java 2 class-files via scripts written in Ruby language. There are class-file disassembler, assembler and simple Ruby to Java bytecode compiler. The work is at the start point.