arm: Thumb ALL the things!

This patch switches every last part of Coreboot on ARM over to Thumb
mode: libpayload, the internal libgcc, and assorted assembly files. In
combination with the respective depthcharge patch, this will switch to
Thumb mode right after the entry point of the bootblock and not switch
back to ARM until the final assembly stub that jumps to the kernel.

The required changes to make this work include some new headers and
Makefile flags to handle assembly files (using the unified syntax and
the same helper macros as Linux), modifying our custom-written libgcc
code for 64-bit division to support Thumb (removing some stale old files
that were never really used for clarity), and flipping the general
CFLAGS to Thumb (some more cleanup there as well while I'm at it).

BUG=None
TEST=Snow and Nyan still boot.

Original-Change-Id: I80c04281e3adbf74f9f477486a96b9fafeb455b3
Original-Signed-off-by: Julius Werner <jwerner@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/182212
Original-Reviewed-by: Gabe Black <gabeblack@chromium.org>
(cherry picked from commit 5f65c17cbfae165a95354146ae79e06c512c2c5a)

Conflicts:
	payloads/libpayload/include/arm/arch/asm.h
	src/arch/arm/Makefile.inc
	src/arch/arm/armv7/Makefile.inc

*** There is an issue with what to do with ramstage-S-ccopts, and
*** will need to be covered in additional ARM cleanup patches.

Change-Id: I80c04281e3adbf74f9f477486a96b9fafeb455b3
Signed-off-by: Marc Jones <marc.jones@se-eng.com>
Reviewed-on: http://review.coreboot.org/6930
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

2 files changed, 19 insertions, 7 deletions

diff --git a/payloads/libpayload/arch/arm/Makefile.inc b/payloads/libpayload/arch/arm/Makefile.inc
index 0078ffe845..2f8da1570a 100644
--- a/payloads/libpayload/arch/arm/Makefile.inc
+++ b/payloads/libpayload/arch/arm/Makefile.inc
@@ -27,7 +27,8 @@
 ## SUCH DAMAGE.
 ##
 
-CFLAGS += -mfloat-abi=hard -marm -mabi=aapcs-linux -march=armv7-a
+CFLAGS += -mthumb -march=armv7-a
+arm_asm_flags = -Wa,-mthumb -Wa,-mimplicit-it=always -Wa,-mno-warn-deprecated
 
 head.o-y += head.S
 libc-y += main.c sysinfo.c
@@ -37,3 +38,7 @@ libc-y += memcpy.S memset.S memmove.S
 libc-y += exception_asm.S exception.c
 libc-y += cache.c cpu.S
 libcbfs-$(CONFIG_LP_CBFS) += dummy_media.c
+
+# Add other classes here when you put assembly files into them!
+head.o-S-ccopts += $(arm_asm_flags)
+libc-S-ccopts += $(arm_asm_flags)
diff --git a/payloads/libpayload/include/arm/arch/asm.h b/payloads/libpayload/include/arm/arch/asm.h
index 2f8859939c..9e9e7ceff4 100644
--- a/payloads/libpayload/include/arm/arch/asm.h
+++ b/payloads/libpayload/include/arm/arch/asm.h
@@ -20,16 +20,17 @@
 #ifndef __ARM_ASM_H
 #define __ARM_ASM_H
 
-#if defined __arm__
-#  define ARM(x...)	x
-#  define THUMB(x...)
-#  define W(instr)	instr
-#elif defined __thumb__
+/* __arm__ is defined regardless of Thumb mode, so need to order this right */
+#if defined __thumb2__
 #  define ARM(x...)
 #  define THUMB(x...)	x
 #  define W(instr)	instr.w
+#elif defined __thumb__
+#  error You are not compiling Thumb2, this won't work!
 #else
-#  error Not in ARM or thumb mode!
+#  define ARM(x...)	x
+#  define THUMB(x...)
+#  define W(instr)	instr
 #endif
 
 #define ALIGN .align 0
@@ -46,4 +47,10 @@
 #define END(name) \
 	.size name, .-name
 
+/* Everything should go into the text section by default. */
+	.text
+
+/* Thumb code uses the (new) unified assembly syntax. */
+THUMB(	.syntax unified )
+
 #endif	/* __ARM_ASM_H */