24.5.3. gem5 GDB step debug secondary cores
gem5’s secondary core GDB setup is a hack and spawns one gdbserver for each core in separate ports, e.g. 7000, 7001, etc.
Partly because of this, it is basically unusable/very hard to use, because you can’t attach to a core that is stopped either because it hasn’t been initialized, or if you are already currently debugging another core.
This affects both full system and userland, and is described in more detail at: https://gem5.atlassian.net/browse/GEM5-626
In LKMC 0a3ce2f41f12024930bcdc74ff646b66dfc46999, we can easily test attaching to another core by passing --run-id, e.g. to connect to the second core we can use --run-id 1:
./run-gdb --arch aarch64 --emulator gem5 --userland userland/gcc/busy_loop.c --run-id 1