btrfs-progs: fix unaligned access in raid6 calculations

The raid6 code matches kernel implementation that also does the
unaligned access. So to keep the code close, add helpers for unaligned
native access and use them. The helpers are local as we don't plan to
use them elsewhere.

Reported-by: Anatoly Pugachev <matorola@gmail.com>
Signed-off-by: David Sterba <dsterba@suse.com>

raid6.c

@@ -10,6 +10,10 @@
  *
  * ----------------------------------------------------------------------- */
 
+/*
+ * Added helpers for unaligned native int access
+ */
+
 /*
  * raid6int1.c
  *
@@ -33,11 +37,15 @@
 # define NSIZE  8
 # define NSHIFT 3
 typedef uint64_t unative_t;
+#define put_unaligned_native(val,p)	put_unaligned_64((val),(p))
+#define get_unaligned_native(p)		get_unaligned_64((p))
 #else
 # define NBYTES(x) ((x) * 0x01010101U)
 # define NSIZE  4
 # define NSHIFT 2
 typedef uint32_t unative_t;
+#define put_unaligned_native(val,p)	put_unaligned_32((val),(p))
+#define get_unaligned_native(p)		get_unaligned_32((p))
 #endif
 
 /*
@@ -84,18 +92,18 @@ void raid6_gen_syndrome(int disks, size_t bytes, void **ptrs)
 	q = dptr[z0+2];		/* RS syndrome */
 
 	for ( d = 0 ; d < bytes ; d += NSIZE*1 ) {
-		wq0 = wp0 = *(unative_t *)&dptr[z0][d+0*NSIZE];
+		wq0 = wp0 = get_unaligned_native(&dptr[z0][d+0*NSIZE]);
 		for ( z = z0-1 ; z >= 0 ; z-- ) {
-			wd0 = *(unative_t *)&dptr[z][d+0*NSIZE];
+			wd0 = get_unaligned_native(&dptr[z][d+0*NSIZE]);
 			wp0 ^= wd0;
 			w20 = MASK(wq0);
 			w10 = SHLBYTE(wq0);
 			w20 &= NBYTES(0x1d);
 			w10 ^= w20;
 			wq0 = w10 ^ wd0;
 		}
-		*(unative_t *)&p[d+NSIZE*0] = wp0;
-		*(unative_t *)&q[d+NSIZE*0] = wq0;
+		put_unaligned_native(wp0, &p[d+NSIZE*0]);
+		put_unaligned_native(wq0, &q[d+NSIZE*0]);
 	}
 }