armv7: init stack to 0xdeadbeef to detect stack overflows

This adds a simple loop which initializes the stack to 0xdeadbeef
which is used by checkstack().

Change-Id: I8aecf7bfb1067de68c4080c1fcb7eefa28fd04a7
Signed-off-by: David Hendricks <dhendrix@chromium.org>
Reviewed-on: http://review.coreboot.org/2421
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

src/arch/armv7/bootblock.inc

@@ -71,6 +71,21 @@ reset:
 	cmp r1, #0
 	bne wait_for_interrupt		@ If this is not core0, wait
 
+	/*
+	 * Initialize the stack to a known value. This is used to check for
+	 * stack overflow later in the boot process.
+	 */
+	ldr	r0, .Stack
+	ldr	r1, .Stack_size
+	sub	r0, r0, r1
+	ldr	r1, .Stack
+	ldr	r2, =0xdeadbeef
+init_stack_loop:
+	str	r2, [r0]
+	add	r0, #4
+	cmp	r0, r1
+	bne	init_stack_loop
+
 /* Set stackpointer in internal RAM to call board_init_f */
 call_bootblock:
 	ldr	sp, .Stack /* Set up stack pointer */
@@ -95,3 +110,6 @@ wait_for_interrupt:
 .align 2
 .Stack:
 	.word CONFIG_STACK_TOP
+.align 2
+.Stack_size:
+	.word CONFIG_STACK_SIZE