#include <stdio.h>
#include <iostream.h>

void backtrace();

int main()
{
   backtrace();
   return 0;
}

void backtrace()
{
// At first I fetch the interesting registers ...
// I'll write sp for stack pointer and fp for fp
   register long unsigned *plFp asm("r3");   // fp or old sp
   register long unsigned *plSp asm("r30");  // sp
   register long unsigned *r2 asm("r2");     // rp
   
// To get the return pointer rp I could use r2 but I want to
// walk from sp because I can't get r2 and rp of the functionsi that called
// backtrace

  unsigned long *plStack, *saved_rp,  *pc;
  saved_rp = (unsigned long*)((long)(plSp)- 4*5); // or // saved_rp = plSp - 5;
  // At http://devrsrc1.external.hp.com/STK/partner/rad_11_0_32.pdf 
  // p. 72 I've read that at the position sp - 20 Byte
  // the saved rp can be fetched. This works.
  cout << "The adresses: saved_rp = " << saved_rp << ", plSp = "  << plSp << endl;
  
  pc = (unsigned long*)(*saved_rp + 5); // 

  cout << "r2  = " << r2 << "  pc = " << pc << " *saved_rp  = " << *saved_rp << endl;

  // But at the same page can be read that at sp - 4 the previous
  // sp can be fetched. Sadly that doesn't work ;(
  plStack = (unsigned long*)((long)(plSp) - 4);
  cout << "sp  = " << plSp  <<" fp  = " << plFp  << " plStack  = " << plStack << endl
       << "*sp = " << *plSp <<" *fp = " << *plFp << " *plStack = " << *plStack << endl;
  // also the program shows *plSp != 1 gdb shows 1 here

}