View source for How does Newlib initialize the heap?

== '''How does Newlib initialize the heap? (RL78, RX, ARM targets)''' ==

When using the '''Newlib Library''', the user must overwrite the _sbrk/sbrk_r function implemented in newlib. This is the function malloc() uses in order to define how much space is needed for an allocation.

Below are some examples of the default _sbrk function, depending on the toolchain used:

'''RL78:'''

  char *
  _sbrk (int adj)
  {
    extern char    end; //end of the bss section (start of heap)
    static char *  heap = & end;
    char *         rv = heap;
    char *	 heaptop = (char *) &adj;
  
    heap += adj;
  
        /* The allocated chunk spans our stack?  */
   if (rv < heaptop && heap > heaptop
        /* The allocated chunk spans our address space?  */
        || heap < rv)
      {
        return (char *) -1;
      }
  
    return rv;
  }

'''RX:'''

  void*
  _sbrk (incr)
       int incr;
  {
     extern char   end; /* Set by linker.  */
     static char * heap_end;
     char *        prev_heap_end;
  
     if (heap_end == 0)
       heap_end = & end;
  
     prev_heap_end = heap_end;
     heap_end += incr;
  
     return (void *) prev_heap_end;
  }

'''ARM:'''
  register char * stack_ptr asm ("sp");
  caddr_t __attribute__((weak))
  _sbrk (int incr)
  {
    extern char   end asm ("end");	/* Defined by the linker.  */
    static char * heap_end;
    char *        prev_heap_end;
  
    if (heap_end == NULL)
      heap_end = & end;
    
    prev_heap_end = heap_end;
    
    if (heap_end + incr > stack_ptr)
      {
        /* Some of the libstdc++-v3 tests rely upon detecting
  	 out of memory errors, so do not abort here.  */
  #if 0
        extern void abort (void);
  
        _write (1, "_sbrk: Heap and stack collision\n", 32);
        
        abort ();
  #else
        errno = ENOMEM;
        return (caddr_t) -1;
  #endif
      }
    
    heap_end += incr;
  
    return (caddr_t) prev_heap_end;
  }

These are the functions to overwrite if there is a need to set your own heap.


== '''How does Newlib initializes the heap? (RL78, RX, ARM targets)''' ==

When using the '''Newlib Library''', the user must overwrite the _sbrk/sbrk_r function implemented in newlib. This is the function malloc() uses in order to define how much space is needed for an allocation.

Below are some examples of the default _sbrk function, depending on the toolchain used:

'''RL78:'''

  char *
  _sbrk (int adj)
  {
    extern char    end; //end of the bss section (start of heap)
    static char *  heap = & end;
    char *         rv = heap;
    char *	 heaptop = (char *) &adj;
  
    heap += adj;
  
        /* The allocated chunk spans our stack?  */
   if (rv < heaptop && heap > heaptop
        /* The allocated chunk spans our address space?  */
        || heap < rv)
      {
        errno = ENOMEM;
        return (char *) -1;
      }
  
    return rv;
  }

'''RX:'''

  extern void __set_heaptop (void * ptr);
  char *
  _sbrk (int adj)
  {
    extern char    end;
    static char *  heap = & end;
    char *         rv = heap;
  
    heap += adj;
    __set_heaptop (heap);
    return rv;
  }


'''ARM:'''
  register char * stack_ptr asm ("sp");
  caddr_t __attribute__((weak))
  _sbrk (int incr)
  {
    extern char   end asm ("end");	/* Defined by the linker.  */
    static char * heap_end;
    char *        prev_heap_end;
  
    if (heap_end == NULL)
      heap_end = & end;
    
    prev_heap_end = heap_end;
    
    if (heap_end + incr > stack_ptr)
      {
        /* Some of the libstdc++-v3 tests rely upon detecting
  	 out of memory errors, so do not abort here.  */
  #if 0
        extern void abort (void);
  
        _write (1, "_sbrk: Heap and stack collision\n", 32);
        
        abort ();
  #else
        errno = ENOMEM;
        return (caddr_t) -1;
  #endif
      }
    
    heap_end += incr;
  
    return (caddr_t) prev_heap_end;
  }

These are the functions to overwrite if there is a need to set your own heap.