ARM: 7880/1: Clear the IT state independent of the Thumb-2 mode

The ARM architecture reference specifies that the IT state bits in the
PSR must be all zeros in ARM mode or behavior is unspecified.  On the
Qualcomm Snapdragon S4/Krait architecture CPUs the processor continues
to consider the IT state bits while in ARM mode.  This makes it so
that some instructions are skipped by the CPU.

Signed-off-by: T.J. Purtell <tj@mobisocial.us>
[rmk+kernel@arm.linux.org.uk: fixed whitespace formatting in patch]
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 10 insertions, 4 deletions

diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
index ab3304225272..1aa5ecdd1b3d 100644
--- a/arch/arm/kernel/signal.c
+++ b/arch/arm/kernel/signal.c
@@ -375,12 +375,18 @@ setup_return(struct pt_regs *regs, struct ksignal *ksig,
                  */
                 thumb = handler & 1;
 
-                if (thumb) {
-                        cpsr |= PSR_T_BIT;
 #if __LINUX_ARM_ARCH__ >= 7
-                        /* clear the If-Then Thumb-2 execution state */
-                        cpsr &= ~PSR_IT_MASK;
+                /*
+                 * Clear the If-Then Thumb-2 execution state
+                 * ARM spec requires this to be all 000s in ARM mode
+                 * Snapdragon S4/Krait misbehaves on a Thumb=>ARM
+                 * signal transition without this.
+                 */
+                cpsr &= ~PSR_IT_MASK;
 #endif
+
+                if (thumb) {
+                        cpsr |= PSR_T_BIT;
                 } else
                         cpsr &= ~PSR_T_BIT;
         }