From 7329cc39818a05c168e7d1e791afb03c089f1933 Mon Sep 17 00:00:00 2001
From: Salvatore Sanfilippo <antirez@gmail.com>
Date: Sun, 19 Feb 2017 15:07:08 +0000
Subject: [PATCH] ARM: Avoid fast path for BITOP.

GCC will produce certain unaligned multi load-store instructions
that will be trapped by the Linux kernel since ARM v6 cannot
handle them with unaligned addresses. Better to use the slower
but safer implementation instead of generating the exception which
should be anyway very slow.
---
 src/bitops.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/bitops.c b/src/bitops.c
index 46eee22c3..7ab72633c 100644
--- a/src/bitops.c
+++ b/src/bitops.c
@@ -654,8 +654,11 @@ void bitopCommand(client *c) {
 
         /* Fast path: as far as we have data for all the input bitmaps we
          * can take a fast path that performs much better than the
-         * vanilla algorithm. */
+         * vanilla algorithm. On ARM we skip the fast path since it will
+         * result in GCC compiling the code using multiple-words load/store
+         * operations that are not supported even in ARM >= v6. */
         j = 0;
+        #ifndef __arm__
         if (minlen >= sizeof(unsigned long)*4 && numkeys <= 16) {
             unsigned long *lp[16];
             unsigned long *lres = (unsigned long*) res;
@@ -716,6 +719,7 @@ void bitopCommand(client *c) {
                 }
             }
         }
+        #endif
 
         /* j is set to the next byte to process by the previous loop. */
         for (; j < maxlen; j++) {