Passing Ada Proc as a C Function Pointer

[Warren <ve3wwg@gmail.com>]

I some types defined as:

  type Thread_Context is private;
  type Stack_Area is new String;
  type Thread_Proc is access procedure;

and an Ada API function:

    procedure Thread_Start(Context : out Thread_Context; Proc :
Thread_Proc; Stack : out Stack_Area) is
        type C_Func_Ptr is access procedure;
        pragma Convention(Convention => C, Entity => C_Func_Ptr);

        procedure avr_thread_start(Context : System.Address;
                    Proc : C_Func_Ptr;
                    Stack : System.Address;
                    Size : Unsigned_16);
        pragma import(C,avr_thread_start,"avr_thread_start");

        Func : C_Func_Ptr := Proc.all'Access;
    begin

 
avr_thread_start(Context'Address,Func,Stack(Stack'First)'Address,Stack'Length);

    end Thread_Start;

Because this part of the Ada code is not working, I'm suspicious that
the passed function pointer is incorrect (I have an all-C thread
example
working).

Is it vital that the Thread_Proc procedure also be declared as

pragma import(C,Proc) ?

I'd prefer not to, if possible.

There are no arguments passed-- I only need to launch the passed
Ada procedure from the C side (in a thread).

The avr_thread_start C routine is declared as:

void avr_thread_start(
  avr_thread_context* context,
  void (*fn)(void),
  uint8_t* stack,
  uint16_t stack_size
);

Warren