ARM: 8671/1: V7M: Preserve registers across switch from Thread to Handler mode

According to ARMv7 ARM, when exception is taken content of r0-r3, r12
is unknown (see ExceptionTaken() pseudocode). Even though existent
implementations keep these register unchanged, preserve them to be in
line with architecture.

Reported-by: Dobromir Stefanov <dobromir.stefanov@arm.com>
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

1 files changed, 2 insertions, 0 deletions

diff --git a/arch/arm/mm/proc-v7m.S b/arch/arm/mm/proc-v7m.S
index 8dea61640cc1..11ae6b847ad0 100644
--- a/arch/arm/mm/proc-v7m.S
+++ b/arch/arm/mm/proc-v7m.S
@@ -135,9 +135,11 @@ __v7m_setup_cont:
         dsb
         mov     r6, lr                  @ save LR
         ldr     sp, =init_thread_union + THREAD_START_SP
+        stmia   sp, {r0-r3, r12}
         cpsie   i
         svc     #0
 1:      cpsid   i
+        ldmia   sp, {r0-r3, r12}
         str     r5, [r12, #11 * 4]      @ restore the original SVC vector entry
         mov     lr, r6                  @ restore LR