arch/arm: add THUMB mode config option

config/arch/arm.in

@@ -13,6 +13,31 @@ config ARCH_arm
       The ARM architecture, as defined by:
         http://www.arm.com/
 
+config ARCH_ARM_MODE
+    string
+    default "arm"   if ARCH_ARM_MODE_ARM
+    default "thumb" if ARCH_ARM_MODE_THUMB
+
+choice
+    bool
+    prompt "Default instruction set mode"
+    default ARCH_ARM_MODE_ARM
+
+config ARCH_ARM_MODE_ARM
+    bool
+    prompt "arm"
+    help
+      Defaults to emitting instructions in the ARM mode.
+
+config ARCH_ARM_MODE_THUMB
+    bool
+    prompt "thumb (EXPERIMENTAL)"
+    depends on EXPERIMENTAL
+    help
+      Defaults to emitting instructions in the THUMB mode.
+
+endchoice
+
 config ARCH_ARM_EABI
     bool
     prompt "Use EABI"

scripts/build/arch/arm.sh

@@ -10,4 +10,14 @@ CT_DoArchTupleValues() {
         uClibc,y)   CT_TARGET_SYS=uclibcgnueabi;;
         *,y)        CT_TARGET_SYS=eabi;;
     esac
+
+    # Set the default instrcution set mode
+    case "${CT_ARCH_ARM_MODE}" in
+        arm)    ;;
+        thumb)
+            CT_ARCH_CC_CORE_EXTRA_CONFIG="--with-mode=thumb"
+            CT_ARCH_CC_EXTRA_CONFIG="--with-mode=thumb"
+#            CT_ARCH_TARGET_CFLAGS="-mthumb"
+            ;;
+    esac
 }