ARM: 7031/1: entry: Fix Thumb-2 undef handling for multi-CPU kernels

When v6 and >=v7 boards are supported in the same kernel, the
__und_usr code currently makes a build-time assumption that Thumb-2
instructions occurring in userspace don't need to be supported.
Strictly speaking this is incorrect.

This patch fixes the above case by doing a run-time check on the
CPU architecture in these cases.  This only affects kernels which
support v6 and >=v7 CPUs together: plain v6 and plain v7 kernels
are unaffected.

Signed-off-by: Dave Martin <dave.martin@linaro.org>
Reviewed-by: Jon Medhurst <tixy@yxit.co.uk>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 37 insertions, 1 deletions

diff --git a/arch/arm/kernel/entry-armv.S b/arch/arm/kernel/entry-armv.S
index b7236d400ae..9ad50c4208a 100644
--- a/arch/arm/kernel/entry-armv.S
+++ b/arch/arm/kernel/entry-armv.S
@@ -24,6 +24,7 @@
 #include <asm/unwind.h>
 #include <asm/unistd.h>
 #include <asm/tls.h>
+#include <asm/system.h>
 
 #include "entry-header.S"
 #include <asm/entry-macro-multi.S>
@@ -439,7 +440,27 @@ __und_usr:
 #endif
         beq     call_fpe
         @ Thumb instruction
-#if __LINUX_ARM_ARCH__ >= 7
+#if CONFIG_ARM_THUMB && __LINUX_ARM_ARCH__ >= 6 && CONFIG_CPU_V7
+/*
+ * Thumb-2 instruction handling.  Note that because pre-v6 and >= v6 platforms
+ * can never be supported in a single kernel, this code is not applicable at
+ * all when __LINUX_ARM_ARCH__ < 6.  This allows simplifying assumptions to be
+ * made about .arch directives.
+ */
+#if __LINUX_ARM_ARCH__ < 7
+/* If the target CPU may not be Thumb-2-capable, a run-time check is needed: */
+#define NEED_CPU_ARCHITECTURE
+        ldr     r5, .LCcpu_architecture
+        ldr     r5, [r5]
+        cmp     r5, #CPU_ARCH_ARMv7
+        blo     __und_usr_unknown
+/*
+ * The following code won't get run unless the running CPU really is v7, so
+ * coding round the lack of ldrht on older arches is pointless.  Temporarily
+ * override the assembler target arch with the minimum required instead:
+ */
+        .arch   armv6t2
+#endif
 2:
  ARM(   ldrht   r5, [r4], #2    )
  THUMB( ldrht   r5, [r4]        )
@@ -449,7 +470,16 @@ __und_usr:
 3:      ldrht   r0, [r4]
         add     r2, r2, #2                      @ r2 is PC + 2, make it PC + 4
         orr     r0, r0, r5, lsl #16
+
+#if __LINUX_ARM_ARCH__ < 7
+/* If the target arch was overridden, change it back: */
+#ifdef CONFIG_CPU_32v6K
+        .arch   armv6k
 #else
+        .arch   armv6
+#endif
+#endif /* __LINUX_ARM_ARCH__ < 7 */
+#else /* !(CONFIG_ARM_THUMB && __LINUX_ARM_ARCH__ >= 6 && CONFIG_CPU_V7) */
         b       __und_usr_unknown
 #endif
  UNWIND(.fnend          )
@@ -576,6 +606,12 @@ call_fpe:
         movw_pc lr                              @ CP#14 (Debug)
         movw_pc lr                              @ CP#15 (Control)
 
+#ifdef NEED_CPU_ARCHITECTURE
+        .align  2
+.LCcpu_architecture:
+        .word   __cpu_architecture
+#endif
+
 #ifdef CONFIG_NEON
         .align  6