arm: Move libgcc assembly macros to arch/asm.h

libgcc/macros.h contains some useful assembly macros that are common in
Linux kernel code and facilitate things such as unified ARM/THUMB
assembly. This patch moves it to a more general place where it can be
used by other code as well.

Change-Id: If68e8930aaafa706c54cf9a156fac826b31bb193
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/182178
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>
(cherry picked from commit a780670def94a969829811fa8cf257f12b88f085)
Signed-off-by: Isaac Christensen <isaac.christensen@se-eng.com>
Reviewed-on: http://review.coreboot.org/6917
Tested-by: build bot (Jenkins)
Reviewed-by: David Hendricks <dhendrix@chromium.org>

payloads/libpayload/arch/arm/head.S

@@ -27,17 +27,16 @@
  * SUCH DAMAGE.
  */
 
-	.global _entry, _leave
-	.text
-	.align 4
+#include <arch/asm.h>
 
 1:
+.align 4
 .word	_stack
 
 /*
  * Our entry point
  */
-_entry:
+ENTRY(_entry)
 
 	/* TODO: disable interrupts */
 
@@ -46,14 +45,15 @@ _entry:
 	/* Setup new stack */
 	ldr sp, 1b
 
-	/* TODO: Save old stack pointer */
+	/* TODO: Save old stack pointer and link register */
 
 	/* Let's rock. */
-	b start_main
+	bl start_main
 
-	/* %eax has the return value - pass it on unmolested */
-_leave:
-	/* TODO: restore old stack pointer. */
+	/* %r0 has the return value - pass it on unmolested */
+
+	/* TODO: restore old stack pointer and link register */
 
 	/* Return to the original context. */
-	mov pc, lr
+	bx lr
+ENDPROC(_entry)

payloads/libpayload/arch/arm/util.S

@@ -27,11 +27,9 @@
  * SUCH DAMAGE.
  */
 
-	.global halt
-	.text
-	.align 4
+#include <arch/asm.h>
 
 /* This function puts the system into a halt. */
-	.type halt, function
-halt:
+ENTRY(halt)
 	b halt
+ENDPROC(halt)