xen: Implement common byte{order,swap}.h

The current swab??() infrastructure is unnecessarily complicated, and can be
replaced entirely with compiler builtins.

All supported compilers provide __BYTE_ORDER__ and __builtin_bswap??().

Nothing in Xen cares about the values of __{BIG,LITTLE}_ENDIAN; just that one
of them is defined.  Therefore, centralise their definitions in xen/config.h

Signed-off-by: Lin Liu <lin.liu@citrix.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

xen/include/xen/byteorder.h

@@ -0,0 +1,44 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef XEN_BYTEORDER_H
+#define XEN_BYTEORDER_H
+
+#include <xen/byteswap.h>
+#include <xen/stdint.h>
+
+#if defined(__LITTLE_ENDIAN)
+
+# define cpu_to_le64(x) ((uint64_t)(x))
+# define le64_to_cpu(x) ((uint64_t)(x))
+# define cpu_to_le32(x) ((uint32_t)(x))
+# define le32_to_cpu(x) ((uint32_t)(x))
+# define cpu_to_le16(x) ((uint16_t)(x))
+# define le16_to_cpu(x) ((uint16_t)(x))
+
+# define cpu_to_be64(x) bswap64(x)
+# define be64_to_cpu(x) bswap64(x)
+# define cpu_to_be32(x) bswap32(x)
+# define be32_to_cpu(x) bswap32(x)
+# define cpu_to_be16(x) bswap16(x)
+# define be16_to_cpu(x) bswap16(x)
+
+#elif defined(__BIG_ENDIAN)
+
+# define cpu_to_le64(x) bswap64(x)
+# define le64_to_cpu(x) bswap64(x)
+# define cpu_to_le32(x) bswap32(x)
+# define le32_to_cpu(x) bswap32(x)
+# define cpu_to_le16(x) bswap16(x)
+# define le16_to_cpu(x) bswap16(x)
+
+# define cpu_to_be64(x) ((uint64_t)(x))
+# define be64_to_cpu(x) ((uint64_t)(x))
+# define cpu_to_be32(x) ((uint32_t)(x))
+# define be32_to_cpu(x) ((uint32_t)(x))
+# define cpu_to_be16(x) ((uint16_t)(x))
+# define be16_to_cpu(x) ((uint16_t)(x))
+
+#else
+# error Unknown Endianness
+#endif /* __*_ENDIAN */
+
+#endif /* XEN_BYTEORDER_H */

xen/include/xen/byteorder/big_endian.h

@@ -1,13 +1,6 @@
 #ifndef __XEN_BYTEORDER_BIG_ENDIAN_H__
 #define __XEN_BYTEORDER_BIG_ENDIAN_H__
 
-#ifndef __BIG_ENDIAN
-#define __BIG_ENDIAN 4321
-#endif
-#ifndef __BIG_ENDIAN_BITFIELD
-#define __BIG_ENDIAN_BITFIELD
-#endif
-
 #include <xen/types.h>
 #include <xen/byteorder/swab.h>
 

xen/include/xen/byteorder/little_endian.h

@@ -1,13 +1,6 @@
 #ifndef __XEN_BYTEORDER_LITTLE_ENDIAN_H__
 #define __XEN_BYTEORDER_LITTLE_ENDIAN_H__
 
-#ifndef __LITTLE_ENDIAN
-#define __LITTLE_ENDIAN 1234
-#endif
-#ifndef __LITTLE_ENDIAN_BITFIELD
-#define __LITTLE_ENDIAN_BITFIELD
-#endif
-
 #include <xen/types.h>
 #include <xen/byteorder/swab.h>
 

xen/include/xen/byteswap.h

@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef XEN_BYTESWAP_H
+#define XEN_BYTESWAP_H
+
+#define bswap16(x) __builtin_bswap16(x)
+#define bswap32(x) __builtin_bswap32(x)
+#define bswap64(x) __builtin_bswap64(x)
+
+#if BITS_PER_LONG == 64
+# define bswapl(x) bswap64(x)
+#elif BITS_PER_LONG == 32
+# define bswapl(x) bswap32(x)
+#endif
+
+#endif /* XEN_BYTESWAP_H */

xen/include/xen/config.h

@@ -108,4 +108,12 @@
 /* It is assumed that sizeof(void *) == __alignof(void *) */
 #define POINTER_ALIGN   __SIZEOF_POINTER__
 
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+# define __LITTLE_ENDIAN
+# define __LITTLE_ENDIAN_BITFIELD
+#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+# define __BIG_ENDIAN
+# define __BIG_ENDIAN_BITFIELD
+#endif
+
 #endif /* __XEN_CONFIG_H__ */