Re: Arm - ravenscar - exceptions - last chance handler

[jan.de.kruyf@gmail.com]

On Saturday, May 30, 2015 at 5:43:38 PM UTC+2, Simon Wright wrote:

> 
> > 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) {}
> }

Thanks, Simon.
See my answer to Bob Duff for the full story. I like your C solution, but in my case I will have to kick the bucket and unload myself. At least I believe thats what expected in linux kernel land.

cheers,

j.