powerpc: Fix Unaligned Loads and Stores

This patch modifies the unaligned access routines of the sstep.c
module so that it properly reverses the bytes of storage operands
in the little endian kernel kernel.   This is implemented by
breaking an unaligned little endian access into a combination of
single byte accesses plus an overal byte reversal operation.
Signed-off-by: Tom Musta <tmusta@gmail.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/lib/sstep.c

@@ -212,11 +212,19 @@ static int __kprobes read_mem_unaligned(unsigned long *dest, unsigned long ea,
 {
 	int err;
 	unsigned long x, b, c;
+#ifdef __LITTLE_ENDIAN__
+	int len = nb; /* save a copy of the length for byte reversal */
+#endif
 
 	/* unaligned, do this in pieces */
 	x = 0;
 	for (; nb > 0; nb -= c) {
+#ifdef __LITTLE_ENDIAN__
+		c = 1;
+#endif
+#ifdef __BIG_ENDIAN__
 		c = max_align(ea);
+#endif
 		if (c > nb)
 			c = max_align(nb);
 		err = read_mem_aligned(&b, ea, c);
@@ -225,7 +233,24 @@ static int __kprobes read_mem_unaligned(unsigned long *dest, unsigned long ea,
 		x = (x << (8 * c)) + b;
 		ea += c;
 	}
+#ifdef __LITTLE_ENDIAN__
+	switch (len) {
+	case 2:
+		*dest = byterev_2(x);
+		break;
+	case 4:
+		*dest = byterev_4(x);
+		break;
+#ifdef __powerpc64__
+	case 8:
+		*dest = byterev_8(x);
+		break;
+#endif
+	}
+#endif
+#ifdef __BIG_ENDIAN__
 	*dest = x;
+#endif
 	return 0;
 }
 
@@ -273,9 +298,29 @@ static int __kprobes write_mem_unaligned(unsigned long val, unsigned long ea,
 	int err;
 	unsigned long c;
 
+#ifdef __LITTLE_ENDIAN__
+	switch (nb) {
+	case 2:
+		val = byterev_2(val);
+		break;
+	case 4:
+		val = byterev_4(val);
+		break;
+#ifdef __powerpc64__
+	case 8:
+		val = byterev_8(val);
+		break;
+#endif
+	}
+#endif
 	/* unaligned or little-endian, do this in pieces */
 	for (; nb > 0; nb -= c) {
+#ifdef __LITTLE_ENDIAN__
+		c = 1;
+#endif
+#ifdef __BIG_ENDIAN__
 		c = max_align(ea);
+#endif
 		if (c > nb)
 			c = max_align(nb);
 		err = write_mem_aligned(val >> (nb - c) * 8, ea, c);