Re: [avr-gcc-list] Finding address of where a function called from

[Dmitry K.]

29 Jan 2004 14:51 Tom Harris wrote:
> Greetings,
>
> For logging purposes I would like the called function to be able to find
> out where it was called _from_. What I have done in the past is to take the
> address of a dummy variable on the stack, add a bit to it and hope that the
> result is the address of the stack with the return in it. Sort of the code
> below (which is off the top of my head and probably doesn't even compile):
>
> #define FIDDLE_FACTOR 4
> void foo() {
>       char dummy;
>
>       uint16_t* whereCalled = *((uint16_t*)(&dummy) + FIDDLE_FACTOR);
>
>       ...
> }
>
> The problem is that as the number of stack reserved for the use of foo()
> changes, so does the size of FIDDLE_FACTOR. Is there a more portable way of
> determining this?
>
> TomH

It is sad. Function `__builtin_return_address' does not work in avr-gcc.
It takes contents of a top of a stack, without consideration his use.

Gcc for i86, pdp-11:  all works correctly.

Example:

   extern void foo (char *);
   extern void *p;
   void foo1 (void)
   {
       char s[10];
       foo(s);
       p= __builtin_return_address(0);
   }

Result:
        ...
        rcall foo
        ldd r24,Y+1     ??? must: Y+1+10
        ldd r25,Y+2
        sts (p)+1,r25
        sts p,r24
/* epilogue: frame size=10 */
        adiw r28,10
        ...