[PATCH v2 06/13] asm-generic: unaligned: remove byteshift helpers

Arnd Bergmann
2021-05-14T10:04:17Z

From: Arnd Bergmann <arnd@arndb.de>

In theory, compilers should be able to work this out themselves so we
can use a simpler version based on the swab() helpers.

I have verified that this works on all supported compiler versions
(gcc-4.9 and up, clang-10 and up). Looking at the object code produced by
gcc-11, I found that the impact is mostly a change in inlining decisions
that lead to slightly larger code.

In other cases, this version produces explicit byte swaps in place of
separate byte access, or comparing against pre-swapped constants.

While the source code is clearly simpler, I have not seen an indication
of the new version actually producing better code on Arm, so maybe
we want to skip this after all. From what I can tell, gcc recognizes
the byteswap pattern in the byteshift.h header and can turn it into
explicit instructions, but it does not turn a __builtin_bswap32() back
into individual bytes when that would result in better output, e.g.
when storing a byte-reversed constant.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
arch/arm/include/asm/unaligned.h | 2 -
include/asm-generic/unaligned.h | 2 -
include/linux/unaligned/be_byteshift.h | 71 --------------------------
include/linux/unaligned/be_struct.h | 30 +++++++++++
include/linux/unaligned/le_byteshift.h | 71 --------------------------
include/linux/unaligned/le_struct.h | 30 +++++++++++
6 files changed, 60 insertions(+), 146 deletions(-)
delete mode 100644 include/linux/unaligned/be_byteshift.h
delete mode 100644 include/linux/unaligned/le_byteshift.h

diff --git a/arch/arm/include/asm/unaligned.h b/arch/arm/include/asm/unaligned.h
index ab905ffcf193..3c5248fb4cdc 100644
--- a/arch/arm/include/asm/unaligned.h
+++ b/arch/arm/include/asm/unaligned.h
@@ -10,13 +10,11 @@

#if defined(__LITTLE_ENDIAN)
# include <linux/unaligned/le_struct.h>
-# include <linux/unaligned/be_byteshift.h>
# include <linux/unaligned/generic.h>
# define get_unaligned __get_unaligned_le
# define put_unaligned __put_unaligned_le
#elif defined(__BIG_ENDIAN)
# include <linux/unaligned/be_struct.h>
-# include <linux/unaligned/le_byteshift.h>
# include <linux/unaligned/generic.h>
# define get_unaligned __get_unaligned_be
# define put_unaligned __put_unaligned_be
diff --git a/include/asm-generic/unaligned.h b/include/asm-generic/unaligned.h
index 374c940e9be1..d79df721ae60 100644
--- a/include/asm-generic/unaligned.h
+++ b/include/asm-generic/unaligned.h
@@ -16,7 +16,6 @@
#if defined(__LITTLE_ENDIAN)
# ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
# include <linux/unaligned/le_struct.h>
-# include <linux/unaligned/be_byteshift.h>
# endif
# include <linux/unaligned/generic.h>
# define get_unaligned __get_unaligned_le
@@ -24,7 +23,6 @@
#elif defined(__BIG_ENDIAN)
# ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
# include <linux/unaligned/be_struct.h>
-# include <linux/unaligned/le_byteshift.h>
# endif
# include <linux/unaligned/generic.h>
# define get_unaligned __get_unaligned_be
diff --git a/include/linux/unaligned/be_byteshift.h b/include/linux/unaligned/be_byteshift.h
deleted file mode 100644
index c43ff5918c8a..000000000000
--- a/include/linux/unaligned/be_byteshift.h
+++ /dev/null
@@ -1,71 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-#ifndef _LINUX_UNALIGNED_BE_BYTESHIFT_H
-#define _LINUX_UNALIGNED_BE_BYTESHIFT_H
-
-#include <linux/types.h>
-
-static inline u16 __get_unaligned_be16(const u8 *p)
-{
- return p[0] << 8 | p[1];
-}
-
-static inline u32 __get_unaligned_be32(const u8 *p)
-{
- return p[0] << 24 | p[1] << 16 | p[2] << 8 | p[3];
-}
-
-static inline u64 __get_unaligned_be64(const u8 *p)
-{
- return (u64)__get_unaligned_be32(p) << 32 |
- __get_unaligned_be32(p + 4);
-}
-
-static inline void __put_unaligned_be16(u16 val, u8 *p)
-{
- *p++ = val >> 8;
- *p++ = val;
-}
-
-static inline void __put_unaligned_be32(u32 val, u8 *p)
-{
- __put_unaligned_be16(val >> 16, p);
- __put_unaligned_be16(val, p + 2);
-}
-
-static inline void __put_unaligned_be64(u64 val, u8 *p)
-{
- __put_unaligned_be32(val >> 32, p);
- __put_unaligned_be32(val, p + 4);
-}
-
-static inline u16 get_unaligned_be16(const void *p)
-{
- return __get_unaligned_be16(p);
-}
-
-static inline u32 get_unaligned_be32(const void *p)
-{
- return __get_unaligned_be32(p);
-}
-
-static inline u64 get_unaligned_be64(const void *p)
-{
- return __get_unaligned_be64(p);
-}
-
-static inline void put_unaligned_be16(u16 val, void *p)
-{
- __put_unaligned_be16(val, p);
-}
-
-static inline void put_unaligned_be32(u32 val, void *p)
-{
- __put_unaligned_be32(val, p);
-}
-
-static inline void put_unaligned_be64(u64 val, void *p)
-{
- __put_unaligned_be64(val, p);
-}
-
-#endif /* _LINUX_UNALIGNED_BE_BYTESHIFT_H */
diff --git a/include/linux/unaligned/be_struct.h b/include/linux/unaligned/be_struct.h
index 15ea503a13fc..76d9fe297c33 100644
--- a/include/linux/unaligned/be_struct.h
+++ b/include/linux/unaligned/be_struct.h
@@ -34,4 +34,34 @@ static inline void put_unaligned_be64(u64 val, void *p)
__put_unaligned_cpu64(val, p);
}

+static inline u16 get_unaligned_le16(const void *p)
+{
+ return swab16(__get_unaligned_cpu16((const u8 *)p));
+}
+
+static inline u32 get_unaligned_le32(const void *p)
+{
+ return swab32(__get_unaligned_cpu32((const u8 *)p));
+}
+
+static inline u64 get_unaligned_le64(const void *p)
+{
+ return swab64(__get_unaligned_cpu64((const u8 *)p));
+}
+
+static inline void put_unaligned_le16(u16 val, void *p)
+{
+ __put_unaligned_cpu16(swab16(val), p);
+}
+
+static inline void put_unaligned_le32(u32 val, void *p)
+{
+ __put_unaligned_cpu32(swab32(val), p);
+}
+
+static inline void put_unaligned_le64(u64 val, void *p)
+{
+ __put_unaligned_cpu64(swab64(val), p);
+}
+
#endif /* _LINUX_UNALIGNED_BE_STRUCT_H */
diff --git a/include/linux/unaligned/le_byteshift.h b/include/linux/unaligned/le_byteshift.h
deleted file mode 100644
index 2248dcb0df76..000000000000
--- a/include/linux/unaligned/le_byteshift.h
+++ /dev/null
@@ -1,71 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-#ifndef _LINUX_UNALIGNED_LE_BYTESHIFT_H
-#define _LINUX_UNALIGNED_LE_BYTESHIFT_H
-
-#include <linux/types.h>
-
-static inline u16 __get_unaligned_le16(const u8 *p)
-{
- return p[0] | p[1] << 8;
-}
-
-static inline u32 __get_unaligned_le32(const u8 *p)
-{
- return p[0] | p[1] << 8 | p[2] << 16 | p[3] << 24;
-}
-
-static inline u64 __get_unaligned_le64(const u8 *p)
-{
- return (u64)__get_unaligned_le32(p + 4) << 32 |
- __get_unaligned_le32(p);
-}
-
-static inline void __put_unaligned_le16(u16 val, u8 *p)
-{
- *p++ = val;
- *p++ = val >> 8;
-}
-
-static inline void __put_unaligned_le32(u32 val, u8 *p)
-{
- __put_unaligned_le16(val >> 16, p + 2);
- __put_unaligned_le16(val, p);
-}
-
-static inline void __put_unaligned_le64(u64 val, u8 *p)
-{
- __put_unaligned_le32(val >> 32, p + 4);
- __put_unaligned_le32(val, p);
-}
-
-static inline u16 get_unaligned_le16(const void *p)
-{
- return __get_unaligned_le16(p);
-}
-
-static inline u32 get_unaligned_le32(const void *p)
-{
- return __get_unaligned_le32(p);
-}
-
-static inline u64 get_unaligned_le64(const void *p)
-{
- return __get_unaligned_le64(p);
-}
-
-static inline void put_unaligned_le16(u16 val, void *p)
-{
- __put_unaligned_le16(val, p);
-}
-
-static inline void put_unaligned_le32(u32 val, void *p)
-{
- __put_unaligned_le32(val, p);
-}
-
-static inline void put_unaligned_le64(u64 val, void *p)
-{
- __put_unaligned_le64(val, p);
-}
-
-#endif /* _LINUX_UNALIGNED_LE_BYTESHIFT_H */
diff --git a/include/linux/unaligned/le_struct.h b/include/linux/unaligned/le_struct.h
index 9977987883a6..22f90a4afaa5 100644
--- a/include/linux/unaligned/le_struct.h
+++ b/include/linux/unaligned/le_struct.h
@@ -34,4 +34,34 @@ static inline void put_unaligned_le64(u64 val, void *p)
__put_unaligned_cpu64(val, p);
}

+static inline u16 get_unaligned_be16(const void *p)
+{
+ return swab16(__get_unaligned_cpu16((const u8 *)p));
+}
+
+static inline u32 get_unaligned_be32(const void *p)
+{
+ return swab32(__get_unaligned_cpu32((const u8 *)p));
+}
+
+static inline u64 get_unaligned_be64(const void *p)
+{
+ return swab64(__get_unaligned_cpu64((const u8 *)p));
+}
+
+static inline void put_unaligned_be16(u16 val, void *p)
+{
+ __put_unaligned_cpu16(swab16(val), p);
+}
+
+static inline void put_unaligned_be32(u32 val, void *p)
+{
+ __put_unaligned_cpu32(swab32(val), p);
+}
+
+static inline void put_unaligned_be64(u64 val, void *p)
+{
+ __put_unaligned_cpu64(swab64(val), p);
+}
+
#endif /* _LINUX_UNALIGNED_LE_STRUCT_H */
--
2.29.2