[PATCH v3 1/6] xen: implement byteswap

[Lin Liu <lin.liu@citrix.com>]

swab() is massively over complicated and can be simplified by builtins.
The compilers provide builtin function to swap bytes.
* gcc:   https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html
* clang: https://clang.llvm.org/docs/LanguageExtensions.html
This patch simplify swab() with builtins and fallback for old compilers.

Signed-off-by: Lin Liu <lin.liu@citrix.com>
---
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Julien Grall <julien@xen.org>
Cc: Bertrand Marquis <bertrand.marquis@arm.com>
Cc: Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: George Dunlap <george.dunlap@citrix.com>
Cc: Jan Beulich <jbeulich@suse.com>
Cc: Wei Liu <wl@xen.org>
Cc: "Roger Pau Monné" <roger.pau@citrix.com>
Changes in v3:
- Check __has_builtin instead of GNUC version 

Changes in v2:
- Add fallback for compilers without __builtin_bswap
- Implement with plain C instead of macros
---
 xen/arch/arm/include/asm/byteorder.h | 14 ++-----
 xen/arch/x86/include/asm/byteorder.h | 34 ++---------------
 xen/include/xen/byteorder.h          | 56 ++++++++++++++++++++++++++++
 xen/include/xen/byteswap.h           | 44 ++++++++++++++++++++++
 xen/include/xen/compiler.h           | 12 ++++++
 5 files changed, 120 insertions(+), 40 deletions(-)
 create mode 100644 xen/include/xen/byteorder.h
 create mode 100644 xen/include/xen/byteswap.h

diff --git a/xen/arch/arm/include/asm/byteorder.h b/xen/arch/arm/include/asm/byteorder.h
index 9c712c4788..622eeaba07 100644
--- a/xen/arch/arm/include/asm/byteorder.h
+++ b/xen/arch/arm/include/asm/byteorder.h
@@ -1,16 +1,10 @@
 #ifndef __ASM_ARM_BYTEORDER_H__
 #define __ASM_ARM_BYTEORDER_H__
 
-#define __BYTEORDER_HAS_U64__
+#ifndef __BYTE_ORDER__
+   #define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
+#endif
 
-#include <xen/byteorder/little_endian.h>
+#include <xen/byteorder.h>
 
 #endif /* __ASM_ARM_BYTEORDER_H__ */
-/*
- * Local variables:
- * mode: C
- * c-file-style: "BSD"
- * c-basic-offset: 4
- * indent-tabs-mode: nil
- * End:
- */
diff --git a/xen/arch/x86/include/asm/byteorder.h b/xen/arch/x86/include/asm/byteorder.h
index 1f77e502a5..82aadee7bd 100644
--- a/xen/arch/x86/include/asm/byteorder.h
+++ b/xen/arch/x86/include/asm/byteorder.h
@@ -1,36 +1,10 @@
 #ifndef __ASM_X86_BYTEORDER_H__
 #define __ASM_X86_BYTEORDER_H__
 
-#include <asm/types.h>
-#include <xen/compiler.h>
+#ifndef __BYTE_ORDER__
+   #define __BYTE_ORDER__ __ORDER_LITTLE_ENDIAN__
+#endif
 
-static inline __attribute_const__ __u32 ___arch__swab32(__u32 x)
-{
-    asm("bswap %0" : "=r" (x) : "0" (x));
-    return x;
-}
-
-static inline __attribute_const__ __u64 ___arch__swab64(__u64 val)
-{ 
-    union { 
-        struct { __u32 a,b; } s;
-        __u64 u;
-    } v;
-    v.u = val;
-    asm("bswapl %0 ; bswapl %1 ; xchgl %0,%1" 
-        : "=r" (v.s.a), "=r" (v.s.b) 
-        : "0" (v.s.a), "1" (v.s.b)); 
-    return v.u;
-} 
-
-/* Do not define swab16.  Gcc is smart enough to recognize "C" version and
-   convert it into rotation or exhange.  */
-
-#define __arch__swab64(x) ___arch__swab64(x)
-#define __arch__swab32(x) ___arch__swab32(x)
-
-#define __BYTEORDER_HAS_U64__
-
-#include <xen/byteorder/little_endian.h>
+#include <xen/byteorder.h>
 
 #endif /* __ASM_X86_BYTEORDER_H__ */
diff --git a/xen/include/xen/byteorder.h b/xen/include/xen/byteorder.h
new file mode 100644
index 0000000000..2ec434e6a6
--- /dev/null
+++ b/xen/include/xen/byteorder.h
@@ -0,0 +1,56 @@
+#ifndef __XEN_BYTEORDER_H__
+#define __XEN_BYTEORDER_H__
+
+#include <xen/byteswap.h>
+
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+
+# ifndef __LITTLE_ENDIAN
+#  define __LITTLE_ENDIAN 1234
+# endif
+
+# ifndef __LITTLE_ENDIAN_BITFIELD
+#  define __LITTLE_ENDIAN_BITFIELD
+# endif
+
+# define cpu_to_le64(x) (x)
+# define le64_to_cpu(x) (x)
+# define cpu_to_le32(x) (x)
+# define le32_to_cpu(x) (x)
+# define cpu_to_le16(x) (x)
+# define le16_to_cpu(x) (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 __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+
+# ifndef __BIG_ENDIAN
+#  define __BIG_ENDIAN 4321
+# endif
+
+# ifndef __BIG_ENDIAN_BITFIELD
+#  define __BIG_ENDIAN_BITFIELD
+# endif
+
+# 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) (x)
+# define be64_to_cpu(x) (x)
+# define cpu_to_be32(x) (x)
+# define be32_to_cpu(x) (x)
+# define cpu_to_be16(x) (x)
+# define be16_to_cpu(x) (x)
+
+#else
+# error "Unknown Endianness"
+#endif /* __BYTE_ORDER__ */
+
+#endif /* __XEN_BYTEORDER_H__ */
diff --git a/xen/include/xen/byteswap.h b/xen/include/xen/byteswap.h
new file mode 100644
index 0000000000..0dd5567557
--- /dev/null
+++ b/xen/include/xen/byteswap.h
@@ -0,0 +1,44 @@
+#ifndef __XEN_BYTESWAP_H__
+#define __XEN_BYTESWAP_H__
+
+#include <xen/types.h>
+#include <xen/lib.h>
+
+#if !__has_builtin(__builtin_bswap16)
+static always_inline uint16_t __builtin_bswap16(uint16_t val)
+{
+    return ((val & 0x00FF) << 8) | ((val & 0xFF00) >> 8);
+}
+#endif
+
+#if !__has_builtin(__builtin_bswap32)
+static always_inline uint32_t __builtin_bswap32(uint32_t val)
+{
+    return ((val & 0x000000FF) << 24) |
+           ((val & 0x0000FF00) <<  8) |
+           ((val & 0x00FF0000) >>  8) |
+           ((val & 0xFF000000) >> 24);
+}
+#endif
+
+#if !__has_builtin(__builtin_bswap64)
+static always_inline uint64_t __builtin_bswap64(uint64_t val)
+{
+    return ((val & 0x00000000000000FF) << 56) |
+           ((val & 0x000000000000FF00) << 40) |
+           ((val & 0x0000000000FF0000) << 24) |
+           ((val & 0x00000000FF000000) <<  8) |
+           ((val & 0x000000FF00000000) >>  8) |
+           ((val & 0x0000FF0000000000) >> 24) |
+           ((val & 0x00FF000000000000) >> 40) |
+           ((val & 0xFF00000000000000) >> 56);
+}
+#endif
+
+#define bswap16(x) __builtin_bswap16(x)
+#define bswap32(x) __builtin_bswap32(x)
+#define bswap64(x) __builtin_bswap64(x)
+
+#define bswap_ul(x) PASTE(bswap,BITS_PER_LONG)(x)
+
+#endif /* __XEN_BYTESWAP_H__ */
diff --git a/xen/include/xen/compiler.h b/xen/include/xen/compiler.h
index 933aec09a9..05b1b8b24d 100644
--- a/xen/include/xen/compiler.h
+++ b/xen/include/xen/compiler.h
@@ -185,4 +185,16 @@
 # define CLANG_DISABLE_WARN_GCC_COMPAT_END
 #endif
 
+#ifndef __has_builtin
+/*
+ * Backwards compatibility for GCC < 10.
+ * All supported versions of Clang support __has_builtin
+ * */
+#define __has_builtin(x) GCC_has ## x
+
+#define GCC_has__builtin_bswap16 (CONFIG_GCC_VERSION >= 40800)
+#define GCC_has__builtin_bswap32 (CONFIG_GCC_VERSION >= 40400)
+#define GCC_has__builtin_bswap64 (CONFIG_GCC_VERSION >= 40400)
+#endif
+
 #endif /* __LINUX_COMPILER_H */
-- 
2.27.0