Thumb-2: Add Thumb-2 support to the build files

This patch adds the necessary entries to the Makefile and Kconfig
files for building the Thumb-2 kernel.
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm/Kconfig

@@ -669,6 +669,23 @@ config HZ
 	default OMAP_32K_TIMER_HZ if ARCH_OMAP && OMAP_32K_TIMER
 	default 100
 
+config THUMB2_KERNEL
+	bool "Compile the kernel in Thumb-2 mode"
+	depends on CPU_V7 && EXPERIMENTAL
+	default n
+	select AEABI
+	select ARM_ASM_UNIFIED
+	help
+	  By enabling this option, the kernel will be compiled in
+	  Thumb-2 mode. A compiler/assembler that understand the unified
+	  ARM-Thumb syntax is needed.
+
+	  If unsure, say N.
+
+config ARM_ASM_UNIFIED
+	bool
+	default n
+
 config AEABI
 	bool "Use the ARM EABI to compile the kernel"
 	help

arch/arm/Kconfig.debug

@@ -8,7 +8,7 @@ source "lib/Kconfig.debug"
 # n, but then RMK will have to kill you ;).
 config FRAME_POINTER
 	bool
-	default y
+	default y if !THUMB2_KERNEL
 	help
 	  If you say N here, the resulting kernel will be slightly smaller and
 	  faster. However, when a problem occurs with the kernel, the

arch/arm/Makefile

@@ -84,9 +84,16 @@ else
 CFLAGS_ABI	:=$(call cc-option,-mapcs-32,-mabi=apcs-gnu) $(call cc-option,-mno-thumb-interwork,)
 endif
 
+ifeq ($(CONFIG_THUMB2_KERNEL),y)
+# We currently suppress all the gas warnings but finer-grained option
+# will be provided for the unified assembly syntax
+CFLAGS_THUMB2	:=-mthumb -Wa$(comma)-W
+AFLAGS_THUMB2	:=-Wa$(comma)-mthumb -Wa$(comma)-W
+endif
+
 # Need -Uarm for gcc < 3.x
-KBUILD_CFLAGS	+=$(CFLAGS_ABI) $(arch-y) $(tune-y) $(call cc-option,-mshort-load-bytes,$(call cc-option,-malignment-traps,)) -msoft-float -Uarm
-KBUILD_AFLAGS	+=$(CFLAGS_ABI) $(arch-y) $(tune-y) -msoft-float
+KBUILD_CFLAGS	+=$(CFLAGS_ABI) $(CFLAGS_THUMB2) $(arch-y) $(tune-y) $(call cc-option,-mshort-load-bytes,$(call cc-option,-malignment-traps,)) -msoft-float -Uarm
+KBUILD_AFLAGS	+=$(CFLAGS_ABI) $(AFLAGS_THUMB2) $(arch-y) $(tune-y) -msoft-float
 
 CHECKFLAGS	+= -D__arm__