Debug Session (Debugging with GDB)

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20.5.3 Putting it All Together

In summary, when your program is ready to debug, you must follow these steps.

  1. Make sure you have defined the supporting low-level routines (see What You Must Do for the Stub): getDebugChar, putDebugChar, flush_i_cache, memset, exceptionHandler.
  2. Insert these lines in your program’s startup code, before the main procedure is called:

    set_debug_traps(); breakpoint();

    On some machines, when a breakpoint trap is raised, the hardware automatically makes the PC point to the instruction after the breakpoint. If your machine doesn’t do that, you may need to adjust handle_exception to arrange for it to return to the instruction after the breakpoint on this first invocation, so that your program doesn’t keep hitting the initial breakpoint instead of making progress.
  3. For the 680x0 stub only, you need to provide a variable called exceptionHook. Normally you just use:

    void (*exceptionHook)() = 0;

    but if before calling set_debug_traps, you set it to point to a function in your program, that function is called when GDB continues after stopping on a trap (for example, bus error). The function indicated by exceptionHook is called with one parameter: an int which is the exception number.
  4. Compile and link together: your program, the GDB debugging stub for your target architecture, and the supporting subroutines.
  5. Make sure you have a serial connection between your target machine and the GDB host, and identify the serial port on the host.
  6. Download your program to your target machine (or get it there by whatever means the manufacturer provides), and start it.
  7. Start GDB on the host, and connect to the target (see Connecting to a Remote Target).

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