; ***********************************************************************
; *									*
; *           A Simple Implementation of malloc() and free()            *
; *									*
; ***********************************************************************

; Author:   John Zaitseff <J.Zaitseff@unsw.edu.au>
; Date:     5th April, 2003
; Version:  1.1

; This file provides the an extremely simple implementation of the functions
; "malloc" and "free".  This allows the GNU Debugger to interactively call
; assembly language programs that manipulate strings.  In other words, this
; allows the GNU Debugger to call a function within the assembly language
; program when using the debugger "print" command with string arguments.


; -----------------------------------------------------------------------
; Assembly language preamble and constant values

	.set	NULL, 0			; A NULL pointer in C

	.text
	.align


; -----------------------------------------------------------------------
; Function: void *malloc (size_t size)

; This Standard C function is meant to return a pointer to space for an
; object of size "size", or NULL if the request cannot be satisfied.  The
; space is uninitialised.

; This particular implementation of malloc() simply returns a pointer to
; a block of memory.  This means that malloc() can only be used ONCE in
; the program!  Although this might seem like a major limitation, it is
; only meant to be used by the GNU Debugger (via the "print" command) for
; calling functions with a SINGLE "char *" parameter.


	.global	malloc
	.type	malloc, function

malloc:
	ldr	r1, =malloc_block_size	; Check if client wants to malloc
	cmp	r0, r1			; more memory than is available
	movhs	r0, #NULL		; Yes: return NULL
	ldrlo	r0, =malloc_block	; No: return a pointer to the block
	mov	pc, lr			; Return to the caller

	.size	malloc, .-malloc


; -----------------------------------------------------------------------
; Function: void free (void *p)

; This Standard C function is meant to deallocate the memory pointed to by
; the pointer "p".

; This particular implementation of free() does nothing.


	.global	free
	.type	free, function

free:	mov	pc, lr			; Return to the caller

	.size	free, .-free


; -----------------------------------------------------------------------
; Allocate uninitialised space for malloc()

	.bss


malloc_block:
	.skip	8192			; Allow 8KB for malloc()
malloc_block_end:

	.set	malloc_block_size, (malloc_block_end - malloc_block)


	.end