(For the unfamiliar - the idea is that "gdb server" code runs directly on the CPU and talks to gdb, you can do interactive debugging without special hardware. It can be an alternative to having external JTAG hardware and an interface program like xt-ocd or openocd.)
There are 3 projects I know of:
- Cesanta have released a stub that dumps the stack trace to gdb on exception. They plan to expand it. Blog post here. Source here.
- jcmvbkc has an xtensa gdbstub project designed for other processors. Source here.
- Cal (on this forum) is working on a gdb stub project, discussed in the openocd thread a bit. AFAIK not published yet.