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GDB commands

  • next step one line over.
  • continue or c: continue executing up to next break point.
  • break fn_name: break point at function name.
    • There may be many with same name. So we need the path.
      • For example: break gdb_hello_world::__risc_v_rt__main
  • break lineno: break point at line number of currently-focused file.
    • Example: break 19, or br 19.
  • break my_file.rs:lineno: example break main.rs:17.
  • monitor reset halt: restarts and halts it.
  • layout:
    • layout src: shows source code and CLI.
    • layout asm: shows assembly source and CLI.
    • tui disable to disable the layout.
  • info break to show breakpoints
  • info locals to show variables.
  • print x to print variable x. Also print &x prints the address of x.

Exercises

  1. Access exercises/gdb_hello_world
  2. Inspect the configuration files openocd.cfg (for openocd ) and .gdbinit (for gdb).
  3. Execute cargo run, leave out --release to use the development profile.
    • Without it, cargo will remove / optimise lines.
    • We should debug with --release to ensure the best outcomes.
    • But this examples is just to get started.
  4. Run gdb in one terminal window, and openocd in another window (same directory!).
  5. The image shows what gdb should look like at this stage.
    • Should have a breakpoint in _peripherals which means gdb stopped execution there.
    GDB screenshot showing our main.rs source code. It has a B where the breakpoint is.
  6. Add a break point in main.rs where a/=2
  7. print the resulting value.
  8. Exit with Ctrl+D or Ctrl+C.