Disable UBSAN for alignment-sensitive functions when !CAREFUL_ALIGNMENT

rsync sets CAREFUL_ALIGNMENT for architectures which do not support
unaligned access. Disable UBSAN for functions which may use unaligned
accesses when CAREFUL_ALIGNMENT is set.

Bug: #427

byteorder.h

@@ -68,11 +68,34 @@ SIVAL64(char *buf, int pos, int64 val)
 
 #else /* !CAREFUL_ALIGNMENT */
 
+/* We don't want false positives about alignment from UBSAN, see:
+   https://github.com/WayneD/rsync/issues/427#issuecomment-1375132291
+*/
+
+/* From https://gcc.gnu.org/onlinedocs/cpp/Common-Predefined-Macros.html */
+#ifndef GCC_VERSION
+#define GCC_VERSION (__GNUC__ * 10000 \
+                     + __GNUC_MINOR__ * 100 \
+                     + __GNUC_PATCHLEVEL__)
+#endif
+
+#ifndef RSYNC_NO_UBSAN_ATTR
+# ifdef CAREFUL_ALIGNMENT
+#  ifdef __clang__
+#   define RSYNC_NO_UBSAN_ATTR __attribute__((no_sanitize("undefined")))
+#  elif GCC_VERSION >= 409
+#   define RSYNC_NO_UBSAN_ATTR __attribute__((no_sanitize_undefined))
+#  endif
+# else
+#  define RSYNC_NO_UBSAN_ATTR
+# endif
+#endif
+
 /* This handles things for architectures like the 386 that can handle alignment errors.
  * WARNING: This section is dependent on the length of an int32 (and thus a uint32)
  * being correct (4 bytes)!  Set CAREFUL_ALIGNMENT if it is not. */
 
-static inline uint32
+RSYNC_NO_UBSAN_ATTR static inline uint32
 IVALu(const uchar *buf, int pos)
 {
 	union {
@@ -83,7 +106,7 @@ IVALu(const uchar *buf, int pos)
 	return *u.num;
 }
 
-static inline void
+RSYNC_NO_UBSAN_ATTR static inline void
 SIVALu(uchar *buf, int pos, uint32 val)
 {
 	union {
@@ -94,7 +117,7 @@ SIVALu(uchar *buf, int pos, uint32 val)
 	*u.num = val;
 }
 
-static inline int64
+RSYNC_NO_UBSAN_ATTR static inline int64
 IVAL64(const char *buf, int pos)
 {
 	union {
@@ -105,7 +128,7 @@ IVAL64(const char *buf, int pos)
 	return *u.num;
 }
 
-static inline void
+RSYNC_NO_UBSAN_ATTR static inline void
 SIVAL64(char *buf, int pos, int64 val)
 {
 	union {

io.c

@@ -1791,7 +1791,7 @@ uint32 read_uint(int f)
 	return IVAL(b, 0);
 }
 
-int32 read_varint(int f)
+RSYNC_NO_UBSAN_ATTR int32 read_varint(int f)
 {
 	union {
 		char b[5];
@@ -1823,7 +1823,7 @@ int32 read_varint(int f)
 	return u.x;
 }
 
-int64 read_varlong(int f, uchar min_bytes)
+RSYNC_NO_UBSAN_ATTR int64 read_varlong(int f, uchar min_bytes)
 {
 	union {
 		char b[9];