ARM: 6503/1: Thumb-2: Restore sensible zImage header layout for CONFIG_THUMB2_KERNEL

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>

1 files changed, 6 insertions, 1 deletions

diff --git a/arch/arm/boot/compressed/head.S b/arch/arm/boot/compressed/head.S
index be97e0832d7..7193884ed8b 100644
--- a/arch/arm/boot/compressed/head.S
+++ b/arch/arm/boot/compressed/head.S
@@ -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