Re: Arm - ravenscar - exceptions - last chance handler

[Simon Wright <simon@pushface.org>]

jan.de.kruyf@gmail.com writes:

> Could someone interprete this code for me (from the runtime) and advise
>
>    procedure Raise_Exception (E : Exception_Id; Message : String := "") is
>       pragma Unreferenced (E);
>
>       procedure Last_Chance_Handler (Msg : System.Address; Line : Integer);
>       pragma Import (C, Last_Chance_Handler, "__gnat_last_chance_handler");
>       pragma No_Return (Last_Chance_Handler);
>
>    begin
>       Last_Chance_Handler (Message'Address, 0);
>    end Raise_Exception;
>
> end Ada.Exceptions;
> --------------------------------
>
> How is last chance handler going to know the --length-- of the message?
>
> because I like to issue a printk before I die when in the linux kernel.
>
> I have used last chance handler in gdb by looking at the memory, but
> kernel modules are not debugged that way.

FWIW [arm-eabi-]gdb doesn't handle "Msg : System.Address" at all well;
it works much better if you actually write __gnat_last_chance_handler in
C rather than in Ada with an Export:

#include <FreeRTOS.h>
#include <task.h>

__attribute__((weak))
void __gnat_last_chance_handler(const char *message, int line) {
  taskDISABLE_INTERRUPTS();
  vTaskSuspendAll();
  // Loop indefinitely: use the debugger to examine the backtrace.
  while (1) {}
}