path: root/arch/arm/kernel/head-nommu.S
diff options
authorDave Martin <dave.martin@linaro.org>2011-07-13 15:53:30 +0100
committerRussell King <rmk+kernel@arm.linux.org.uk>2011-07-19 12:00:53 +0100
commit540b573875bd26dfe39aa18d22dc195f275fc0df (patch)
treed4fc0c012ef109d601e28814b3806eb44ce357c7 /arch/arm/kernel/head-nommu.S
parentc7e89b16eb90e7bdf0d71bd5ba265ce8d424f30b (diff)
ARM: 6999/1: head, zImage: Always Enter the kernel in ARM state
Currently, the documented kernel entry requirements are not explicit about whether the kernel should be entered in ARM or Thumb, leading to an ambiguitity about how to enter Thumb-2 kernels. As a result, the kernel is reliant on the zImage decompressor to enter the kernel proper in the correct instruction set state. This patch changes the boot entry protocol for head.S and Image to be the same as for zImage: in all cases, the kernel is now entered in ARM. Documentation/arm/Booting is updated to reflect this new policy. A different rule will be needed for Cortex-M class CPUs as and when support for those lands in mainline, since these CPUs don't support the ARM instruction set at all: a note is added to the effect that the kernel must be entered in Thumb on such systems. Signed-off-by: Dave Martin <dave.martin@linaro.org> Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'arch/arm/kernel/head-nommu.S')
1 files changed, 8 insertions, 0 deletions
diff --git a/arch/arm/kernel/head-nommu.S b/arch/arm/kernel/head-nommu.S
index 6b1e0ad9ec3..d46f25968be 100644
--- a/arch/arm/kernel/head-nommu.S
+++ b/arch/arm/kernel/head-nommu.S
@@ -32,8 +32,16 @@
* numbers for r1.
+ .arm
+ THUMB( adr r9, BSYM(1f) ) @ Kernel is always entered in ARM.
+ THUMB( bx r9 ) @ If this is a Thumb-2 kernel,
+ THUMB( .thumb ) @ switch to Thumb now.
+ THUMB(1: )
setmode PSR_F_BIT | PSR_I_BIT | SVC_MODE, r9 @ ensure svc mode
@ and irqs disabled
#ifndef CONFIG_CPU_CP15