[ARM] 3746/2: Userspace helpers must be Thumb mode interworkable

Patch from Nicolas Pitre

The userspace helpers in clean/arch/arm/kernel/entry-armv.S are called
directly in/from userspace. They need to cope with being called from
Thumb code.

Patch below uses the bx interworking instruction when
CONFIG_ARM_THUMB=y.

Based on an earlier patch from Paul Brook <paul@codesourcery.com>

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 12 insertions, 9 deletions

diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index 7ea5f01dfc7b..de4e33137901 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -634,6 +634,14 @@ ENTRY(__switch_to)
  * purpose.
  */
 
+        .macro  usr_ret, reg
+#ifdef CONFIG_ARM_THUMB
+        bx      \reg
+#else
+        mov     pc, \reg
+#endif
+        .endm
+
         .align  5
         .globl  __kuser_helper_start
 __kuser_helper_start:
@@ -675,7 +683,7 @@ __kuser_memory_barrier:				@ 0xffff0fa0
 #if __LINUX_ARM_ARCH__ >= 6 && defined(CONFIG_SMP)
         mcr     p15, 0, r0, c7, c10, 5  @ dmb
 #endif
-        mov     pc, lr
+        usr_ret lr
 
         .align  5
 
@@ -778,7 +786,7 @@ __kuser_cmpxchg:				@ 0xffff0fc0
         mov     r0, #-1
         adds    r0, r0, #0
 #endif
-        mov     pc, lr
+        usr_ret lr
 
 #else
 
@@ -792,7 +800,7 @@ __kuser_cmpxchg:				@ 0xffff0fc0
 #ifdef CONFIG_SMP
         mcr     p15, 0, r0, c7, c10, 5  @ dmb
 #endif
-        mov     pc, lr
+        usr_ret lr
 
 #endif
 
@@ -834,16 +842,11 @@ __kuser_cmpxchg:				@ 0xffff0fc0
 __kuser_get_tls:                                @ 0xffff0fe0
 
 #if !defined(CONFIG_HAS_TLS_REG) && !defined(CONFIG_TLS_REG_EMUL)
-
         ldr     r0, [pc, #(16 - 8)]             @ TLS stored at 0xffff0ff0
-        mov     pc, lr
-
 #else
-
         mrc     p15, 0, r0, c13, c0, 3          @ read TLS register
-        mov     pc, lr
-
 #endif
+        usr_ret lr
 
         .rep    5
         .word   0                       @ pad up to __kuser_helper_version