Run emulator as gdbserver

[jserv]

rISA implements an interesting GDB mode, which runs the simulator as a gdbserver. That is, it allows us to connect RISC-V program with a remote GDB via target remote or target extended-remote -- but without linking in the usual debugging stub. Hopefully, rv32emu can follow the experimental feature in rISA to provide builtin gdbserver.

See also:

• riscv-gdbserver: GDB Server for interacting with RISC-V models, boards and FPGAs

[jserv]

WIP: mini-gdbstub

[RinHizakura]

An experimental solution to this issue is created on my local branch now, which lets rv32emu support a small set of GDB Remote Serial Protocol packet with my mini-gdbstub library.

Here's a small example to play with the debug mode, which shows the convenience to set a breakpoint to stop the emulator by a function symbol.

rv32emu:

$ riscv32-unknown-elf-gcc -g tests/puzzle.c
$ ./build/rv32emu --debug a.out

GDB:

$ riscv32-unknown-elf-gdb
(gdb) file ./a.out 
Reading symbols from ./a.out...
(gdb) target remote :1234
Remote debugging using :1234
0x000100c2 in _start ()
(gdb) set debug remote 1
...
(gdb) break main
...
(gdb) cont
Continuing.
...
argc=0, argv=0xfffff004) at tests/puzzle.c:213
213	    run_puzzle();

A small concern here is that mini-gdbstub is still a WIP and unstable library, so it's not very convenient to use it as a submodule since we may have to sync the library frequently. I'm still thinking if that's a good idea to develop the part of gdbserver as another project. But I think mini-gdbstub is about to be integrated to rv32emu soon.

NOTE: There are still many features and possible bugs that must be refined in mini-gdbstub, and rv32emu also have to provide a better implementation of the gdbstub abstraction (For example, rv_set_bp should be able to set more than one breakpoint).

[jserv]

I'm still thinking if that's a good idea to develop the part of gdbserver as another project. But I think mini-gdbstub is about to be integrated to rv32emu soon.

Both git submodule and in-repository maintenance are fine to me. Pick one when you are ready to submit pull request(s).

[jserv]

See also

• librspd
• orcasim-gdbrsp