ARM: 6503/1: Thumb-2: Restore sensible zImage header layout for CONFIG_THUMB2_KERNEL
Dave Martin [Mon, 29 Nov 2010 18:43:27 +0000 (19:43 +0100)]
The code which makes up the zImage header intends to leave a
32-byte gap followed by a branch to the real entry point, a magic
number, and a word containing the absolute entry point address.

This gets messed up with with CONFIG_THUMB2_KERNEL, because the
size of the initial padding NOPs changes.

Instead, the header can be made fully compatible by restoring it to
ARM.

In the Thumb-2 case, we can replace the initial NOPs with a
sequence which switches to Thumb and jumps to the real entry point.

As a consequence, the zImage entry point is now always ARM, so no
special magic is needed any more for the uImage rules in the
Thumb-2 case.

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

arch/arm/boot/Makefile
arch/arm/boot/compressed/head.S

index 4a590f4..4d26f2c 100644 (file)
@@ -70,12 +70,7 @@ else
 $(obj)/uImage: LOADADDR=$(ZRELADDR)
 endif
 
-ifeq ($(CONFIG_THUMB2_KERNEL),y)
-# Set bit 0 to 1 so that "mov pc, rx" switches to Thumb-2 mode
-$(obj)/uImage: STARTADDR=$(shell echo $(LOADADDR) | sed -e "s/.$$/1/")
-else
 $(obj)/uImage: STARTADDR=$(LOADADDR)
-endif
 
 $(obj)/uImage: $(obj)/zImage FORCE
        $(call if_changed,uimage)
index be97e08..7193884 100644 (file)
@@ -125,9 +125,13 @@ wait:              mrc     p14, 0, pc, c0, c1, 0
  * sort out different calling conventions
  */
                .align
+               .arm                            @ Always enter in ARM state
 start:
                .type   start,#function
-               .rept   8
+ THUMB(                adr     r12, BSYM(1f)   )
+ THUMB(                bx      r12             )
+ THUMB(                .rept   6               )
+ ARM(          .rept   8               )
                mov     r0, r0
                .endr
 
@@ -135,6 +139,7 @@ start:
                .word   0x016f2818              @ Magic numbers to help the loader
                .word   start                   @ absolute load/run zImage address
                .word   _edata                  @ zImage end address
+ THUMB(                .thumb                  )
 1:             mov     r7, r1                  @ save architecture ID
                mov     r8, r2                  @ save atags pointer