The content of the ATAG_CORE tag is optional, according to the
specification.  The existing code that validates the atag list
pointed to by r2 at boot does not accept an empty ATAG_CORE tag.

This patch fixes the test so that the empty tag is accepted as
well as the complete tag.  (This corrects issues observed with
the Apex bootloader, as well as with the kexec mechanism.)

Signed-off-by: Mike Westerhof <mwester@dls.net>
--
PATCH FOLLOWS
KernelVersion: 2.6.24

diff -Naur linux.orig/arch/arm/kernel/head-common.S linux/arch/arm/kernel/head-common.S
--- linux.orig/arch/arm/kernel/head-common.S	2008-02-01 22:21:57.000000000 -0600
+++ linux/arch/arm/kernel/head-common.S	2008-02-01 22:27:14.000000000 -0600
@@ -239,8 +239,11 @@
 
 	ldr	r5, [r2, #0]			@ is first tag ATAG_CORE?
 	subs	r5, r5, #ATAG_CORE_SIZE
+	beq	2f
+	ldr	r5, [r2, #0]
+	subs	r5, r5, #ATAG_CORE_EMPTY_SIZE
 	bne	1f
-	ldr	r5, [r2, #4]
+2:	ldr	r5, [r2, #4]
 	ldr	r6, =ATAG_CORE
 	cmp	r5, r6
 	bne	1f
diff -Naur linux.orig/arch/arm/kernel/head.S linux/arch/arm/kernel/head.S
--- linux.orig/arch/arm/kernel/head.S	2008-02-01 22:21:57.000000000 -0600
+++ linux/arch/arm/kernel/head.S	2008-02-01 22:22:01.000000000 -0600
@@ -30,6 +30,7 @@
 #define KERNEL_RAM_PADDR	(PHYS_OFFSET + TEXT_OFFSET)
 
 #define ATAG_CORE 0x54410001
+#define ATAG_CORE_EMPTY_SIZE ((2*4) >> 2)
 #define ATAG_CORE_SIZE ((2*4 + 3*4) >> 2)