ARM: 6961/1: zImage: Add build-time check for correctly-sized proc_type entries

It is easy to mis-maintain the proc_types table such that the
entries become wrongly-sized and misaligned when the kernel is
built in Thumb-2.

This patch adds an assembly-time check which will turn most common
size/alignment mistakes in this table into build failures, to avoid
having to debug the boot-time kernel hang which would happen if the
resulting kernel were actually booted.

Signed-off-by: Dave Martin <dave.martin@linaro.org>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/boot/compressed/head.S

@@ -597,6 +597,8 @@ __common_mmu_cache_on:
 		sub	pc, lr, r0, lsr #32	@ properly flush pipeline
 #endif
 
+#define PROC_ENTRY_SIZE (4*5)
+
 /*
  * Here follow the relocatable cache support functions for the
  * various processors.  This is a generic hook for locating an
@@ -624,7 +626,7 @@ call_cache_fn:	adr	r12, proc_types
  ARM(		addeq	pc, r12, r3		) @ call cache function
  THUMB(		addeq	r12, r3			)
  THUMB(		moveq	pc, r12			) @ call cache function
-		add	r12, r12, #4*5
+		add	r12, r12, #PROC_ENTRY_SIZE
 		b	1b
 
 /*
@@ -794,6 +796,16 @@ proc_types:
 
 		.size	proc_types, . - proc_types
 
+		/*
+		 * If you get a "non-constant expression in ".if" statement"
+		 * error from the assembler on this line, check that you have
+		 * not accidentally written a "b" instruction where you should
+		 * have written W(b).
+		 */
+		.if (. - proc_types) % PROC_ENTRY_SIZE != 0
+		.error "The size of one or more proc_types entries is wrong."
+		.endif
+
 /*
  * Turn off the Cache and MMU.  ARMv3 does not support
  * reading the control register, but ARMv4 does.