ARC: Unaligned access emulation

ARC700 doesn't natively support unaligned access, but can be emulated
-Unaligned Access Exception
-Disassembly at the Fault address to find the exact insn (long/short)

Also per Arnd's comment, we runtime control it using 2 sysctl knobs:
* SYSCTL_ARCH_UNALIGN_ALLOW: Runtime enable/disble
* SYSCTL_ARCH_UNALIGN_NO_WARN: Warn on each emulation attempt

Originally contributed by Tim Yao <tim.yao@amlogic.com>

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Cc: Tim Yao <tim.yao@amlogic.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>

1 files changed, 11 insertions, 0 deletions

diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
index cde8d3fcec94..f8042835e746 100644
--- a/arch/arc/Kconfig
+++ b/arch/arc/Kconfig
@@ -336,6 +336,17 @@ config ARC_CURR_IN_REG
           This reserved Register R25 to point to Current Task in
           kernel mode. This saves memory access for each such access
 
+
+config ARC_MISALIGN_ACCESS
+        bool "Emulate unaligned memory access (userspace only)"
+        default N
+        select SYSCTL_ARCH_UNALIGN_NO_WARN
+        select SYSCTL_ARCH_UNALIGN_ALLOW
+        help
+          This enables misaligned 16 & 32 bit memory access from user space.
+          Use ONLY-IF-ABS-NECESSARY as it will be very slow and also can hide
+          potential bugs in code
+
 config ARC_STACK_NONEXEC
         bool "Make stack non-executable"
         default n