[PATCH] eal: fix unaligned loads/stores in rte_memcpy_aligned

[Luc Pelletier]

Calls to rte_memcpy_aligned could result in unaligned loads/stores for
1 < n < 16. This is undefined behavior according to the C standard,
and it gets flagged by the clang undefined behavior sanitizer.

rte_memcpy_aligned is called with aligned src and dst addresses. When
n is odd, the code would copy a single byte first, increment src/dst,
then, depending on the value of n, would cast src/dst to a qword, dword
or word pointer. This results in an unaligned load/store. Reversing the
order of the casts & copies (ie. copying a qword first, dword second,
etc.) fixes the issue.

Fixes: d35cc1fe6a7a ("eal/x86: revert select optimized memcpy at run-time")
Cc: Xiaoyun Li <xiaoyun.li at intel.com>
Cc: stable at dpdk.org

Signed-off-by: Luc Pelletier <lucp.at.work at gmail.com>
---
 lib/eal/x86/include/rte_memcpy.h | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/lib/eal/x86/include/rte_memcpy.h b/lib/eal/x86/include/rte_memcpy.h
index 1b6c6e585f..a4eb1316b6 100644
--- a/lib/eal/x86/include/rte_memcpy.h
+++ b/lib/eal/x86/include/rte_memcpy.h
@@ -818,25 +818,25 @@ rte_memcpy_aligned(void *dst, const void *src, size_t n)
 {
 	void *ret = dst;
 
-	/* Copy size <= 16 bytes */
+	/* Copy size < 16 bytes */
 	if (n < 16) {
-		if (n & 0x01) {
-			*(uint8_t *)dst = *(const uint8_t *)src;
-			src = (const uint8_t *)src + 1;
-			dst = (uint8_t *)dst + 1;
-		}
-		if (n & 0x02) {
-			*(uint16_t *)dst = *(const uint16_t *)src;
-			src = (const uint16_t *)src + 1;
-			dst = (uint16_t *)dst + 1;
+		if (n & 0x08) {
+			*(uint64_t *)dst = *(const uint64_t *)src;
+			src = (const uint64_t *)src + 1;
+			dst = (uint64_t *)dst + 1;
 		}
 		if (n & 0x04) {
 			*(uint32_t *)dst = *(const uint32_t *)src;
 			src = (const uint32_t *)src + 1;
 			dst = (uint32_t *)dst + 1;
 		}
-		if (n & 0x08)
-			*(uint64_t *)dst = *(const uint64_t *)src;
+		if (n & 0x02) {
+			*(uint16_t *)dst = *(const uint16_t *)src;
+			src = (const uint16_t *)src + 1;
+			dst = (uint16_t *)dst + 1;
+		}
+		if (n & 0x01)
+			*(uint8_t *)dst = *(const uint8_t *)src;
 
 		return ret;
 	}
-- 
2.25.1