ARM: Allow to compile in thumb-2 mode

This shrinks the resulting binary size by ~25%. Exceptions
are still handled in arm mode, so we have to explicitely
put .arm directives into the exception code. Thumb-2 mode
has been tested on i.MX51 Babbage board.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

arch/arm/Kconfig

@@ -101,6 +101,18 @@ config AEABI
 
 	  To use this you need GCC version 4.0.0 or later.
 
+config THUMB2_BAREBOX
+	select ARM_ASM_UNIFIED
+	depends on CPU_V7
+	bool "Compile barebox in thumb-2 mode (read help)"
+	help
+	  This enables compilation of barebox in thumb-2 mode which generates
+	  ~25% smaller binaries. Arm Assembly code needs some fixups to be able
+	  to work correctly in thumb-2 mode. the barebox core should have these
+	  fixups since most assembly code is derived from the Kernel. However,
+	  your board lowlevel init code may break in thumb-2 mode. You have been
+	  warned.
+
 endmenu
 
 menu "Arm specific settings         "

arch/arm/Makefile

@@ -39,8 +39,15 @@ ifeq ($(CONFIG_ARM_UNWIND),y)
 CFLAGS_ABI	+=-funwind-tables
 endif
 
-CPPFLAGS += $(CFLAGS_ABI) $(arch-y) $(tune-y) -msoft-float
-AFLAGS   += -include asm/unified.h -msoft-float
+ifeq ($(CONFIG_THUMB2_BAREBOX),y)
+AFLAGS_AUTOIT	:=$(call as-option,-Wa$(comma)-mimplicit-it=always,-Wa$(comma)-mauto-it)
+AFLAGS_NOWARN	:=$(call as-option,-Wa$(comma)-mno-warn-deprecated,-Wa$(comma)-W)
+CFLAGS_THUMB2	:=-mthumb $(AFLAGS_AUTOIT) $(AFLAGS_NOWARN)
+AFLAGS_THUMB2	:=$(CFLAGS_THUMB2) -Wa$(comma)-mthumb
+endif
+
+CPPFLAGS += $(CFLAGS_ABI) $(arch-y) $(tune-y) -msoft-float $(CFLAGS_THUMB2)
+AFLAGS   += -include asm/unified.h -msoft-float $(AFLAGS_THUMB2)
 
 # Machine directory name.  This list is sorted alphanumerically
 # by CONFIG_* macro name.

arch/arm/cpu/cpu.c

@@ -26,6 +26,7 @@
  */
 
 #include <common.h>
+#include <init.h>
 #include <command.h>
 #include <cache.h>
 #include <asm/mmu.h>
@@ -89,3 +90,29 @@ void arch_shutdown(void)
 	);
 #endif
 }
+
+#ifdef CONFIG_THUMB2_BAREBOX
+static void thumb2_execute(void *func, int argc, char *argv[])
+{
+	/*
+	 * Switch back to arm mode before executing external
+	 * programs.
+	 */
+	__asm__ __volatile__ (
+		"mov r0, #0\n"
+		"mov r1, %0\n"
+		"mov r2, %1\n"
+		"bx %2\n"
+		:
+		: "r" (argc - 1), "r" (&argv[1]), "r" (func)
+		: "r0", "r1", "r2"
+	);
+}
+
+static int execute_init(void)
+{
+	do_execute = thumb2_execute;
+	return 0;
+}
+postcore_initcall(execute_init);
+#endif

arch/arm/cpu/exceptions.S

@@ -106,6 +106,7 @@ _STACK_START:
  * exception handlers
  */
 	.section ".text","ax"
+	.arm
 
 	.align  5
 .globl undefined_instruction

arch/arm/cpu/start.c

@@ -36,6 +36,7 @@ void __naked __section(.text_entry) start(void)
 void __naked __section(.text_exceptions) exception_vectors(void)
 {
 	__asm__ __volatile__ (
+		".arm\n"
 		"b reset\n"				/* reset */
 #ifdef CONFIG_ARM_EXCEPTIONS
 		"ldr pc, =undefined_instruction\n"	/* undefined instruction */

arch/arm/include/asm/barebox-arm-head.h

@@ -4,6 +4,17 @@
 static inline void barebox_arm_head(void)
 {
 	__asm__ __volatile__ (
+#ifdef CONFIG_THUMB2_BAREBOX
+		".arm\n"
+		"adr r9, 1f + 1\n"
+		"bx r9\n"
+		".thumb\n"
+		"1:\n"
+		"bl reset\n"
+		".rept 10\n"
+		"1: b 1b\n"
+		".endr\n"
+#else
 		"b reset\n"
 		"1: b 1b\n"
 		"1: b 1b\n"
@@ -12,6 +23,7 @@ static inline void barebox_arm_head(void)
 		"1: b 1b\n"
 		"1: b 1b\n"
 		"1: b 1b\n"
+#endif
 		".word 0x65726162\n"			/* 'bare' */
 		".word 0x00786f62\n"			/* 'box' */
 		".word _text\n"				/* text base. If copied there,

arch/arm/include/asm/unified.h

@@ -24,10 +24,10 @@
 	.syntax unified
 #endif
 
-#ifdef CONFIG_THUMB2_KERNEL
+#ifdef CONFIG_THUMB2_BAREBOX
 
 #if __GNUC__ < 4
-#error Thumb-2 kernel requires gcc >= 4
+#error Thumb-2 barebox requires gcc >= 4
 #endif
 
 /* The CPSR bit describing the instruction set (Thumb) */
@@ -40,7 +40,7 @@
 #endif
 #define BSYM(sym)	sym + 1
 
-#else	/* !CONFIG_THUMB2_KERNEL */
+#else	/* !CONFIG_THUMB2_BAREBOX */
 
 /* The CPSR bit describing the instruction set (ARM) */
 #define PSR_ISETSTATE	0
@@ -52,7 +52,7 @@
 #endif
 #define BSYM(sym)	sym
 
-#endif	/* CONFIG_THUMB2_KERNEL */
+#endif	/* CONFIG_THUMB2_BAREBOX */
 
 #ifndef CONFIG_ARM_ASM_UNIFIED
 

arch/arm/lib/armlinux.c

@@ -255,6 +255,7 @@ void start_linux(void *adr, int swap, unsigned long initrd_address,
 {
 	void (*kernel)(int zero, int arch, void *params) = adr;
 	void *params = NULL;
+	int architecture;
 
 	if (oftree) {
 		printf("booting Linux kernel with devicetree\n");
@@ -272,5 +273,19 @@ void start_linux(void *adr, int swap, unsigned long initrd_address,
 		__asm__ __volatile__("mcr p15, 0, %0, c1, c0" :: "r" (reg));
 	}
 
-	kernel(0, armlinux_get_architecture(), params);
+	architecture = armlinux_get_architecture();
+
+#ifdef CONFIG_THUMB2_BAREBOX
+	__asm__ __volatile__ (
+		"mov r0, #0\n"
+		"mov r1, %0\n"
+		"mov r2, %1\n"
+		"bx %2\n"
+		:
+		: "r" (architecture), "r" (params), "r" (kernel)
+		: "r0", "r1", "r2"
+	);
+#else
+	kernel(0, architecture, params);
+#endif
 }

commands/go.c

@@ -62,7 +62,11 @@ static int do_go(struct command *cmdtp, int argc, char *argv[])
 	func = addr;
 
 	shutdown_barebox();
-	func(argc - 1, &argv[1]);
+
+	if (do_execute)
+		do_execute(func, argc - 1, &argv[1]);
+	else
+		func(argc - 1, &argv[1]);
 
 	/*
 	 * The application returned. Since we have shutdown barebox and

common/misc.c

@@ -125,3 +125,6 @@ void perror(const char *s)
 #endif
 }
 EXPORT_SYMBOL(perror);
+
+void (*do_execute)(void *func, int argc, char *argv[]);
+EXPORT_SYMBOL(do_execute);

include/common.h

@@ -146,6 +146,12 @@ unsigned long strtoul_suffix(const char *str, char **endp, int base);
 void start_barebox(void);
 void shutdown_barebox(void);
 
+/*
+ * architectures which have special calling conventions for
+ * executing programs should set this. Used by the 'go' command
+ */
+extern void (*do_execute)(void *func, int argc, char *argv[]);
+
 void arch_shutdown(void);
 
 int run_shell(void);