kernel.h: removed REPEAT_BYTE from kernel.h

This patch creates wordpart.h and includes it in asm/word-at-a-time.h
for all architectures. WORD_AT_A_TIME_CONSTANTS depends on kernel.h
because of REPEAT_BYTE. Moving this to another header and including it
where necessary allows us to not include the bloated kernel.h. Making
this implicit dependency on REPEAT_BYTE explicit allows for later
improvements in the lib/string.c inclusion list.

Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Suggested-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Tanzir Hasan <tanzirh@google.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20231226-libstringheader-v6-1-80aa08c7652c@google.com
Signed-off-by: Kees Cook <keescook@chromium.org>

arch/arm/include/asm/word-at-a-time.h

@@ -8,7 +8,8 @@
  * Little-endian word-at-a-time zero byte handling.
  * Heavily based on the x86 algorithm.
  */
-#include <linux/kernel.h>
+#include <linux/bitops.h>
+#include <linux/wordpart.h>
 
 struct word_at_a_time {
 	const unsigned long one_bits, high_bits;

arch/arm64/include/asm/word-at-a-time.h

@@ -9,7 +9,8 @@
 
 #ifndef __AARCH64EB__
 
-#include <linux/kernel.h>
+#include <linux/bitops.h>
+#include <linux/wordpart.h>
 
 struct word_at_a_time {
 	const unsigned long one_bits, high_bits;

arch/powerpc/include/asm/word-at-a-time.h

@@ -4,8 +4,8 @@
 /*
  * Word-at-a-time interfaces for PowerPC.
  */
-
-#include <linux/kernel.h>
+#include <linux/bitops.h>
+#include <linux/wordpart.h>
 #include <asm/asm-compat.h>
 #include <asm/extable.h>
 

arch/riscv/include/asm/word-at-a-time.h

@@ -10,7 +10,8 @@
 
 
 #include <asm/asm-extable.h>
-#include <linux/kernel.h>
+#include <linux/bitops.h>
+#include <linux/wordpart.h>
 
 struct word_at_a_time {
 	const unsigned long one_bits, high_bits;

arch/s390/include/asm/word-at-a-time.h

@@ -2,7 +2,8 @@
 #ifndef _ASM_WORD_AT_A_TIME_H
 #define _ASM_WORD_AT_A_TIME_H
 
-#include <linux/kernel.h>
+#include <linux/bitops.h>
+#include <linux/wordpart.h>
 #include <asm/asm-extable.h>
 #include <asm/bitsperlong.h>
 

arch/sh/include/asm/word-at-a-time.h

@@ -5,6 +5,8 @@
 #ifdef CONFIG_CPU_BIG_ENDIAN
 # include <asm-generic/word-at-a-time.h>
 #else
+#include <linux/bitops.h>
+#include <linux/wordpart.h>
 /*
  * Little-endian version cribbed from x86.
  */

arch/x86/include/asm/word-at-a-time.h

@@ -2,7 +2,8 @@
 #ifndef _ASM_WORD_AT_A_TIME_H
 #define _ASM_WORD_AT_A_TIME_H
 
-#include <linux/kernel.h>
+#include <linux/bitops.h>
+#include <linux/wordpart.h>
 
 /*
  * This is largely generic for little-endian machines, but the

arch/x86/kvm/mmu/mmu.c

@@ -47,6 +47,7 @@
 #include <linux/kern_levels.h>
 #include <linux/kstrtox.h>
 #include <linux/kthread.h>
+#include <linux/wordpart.h>
 
 #include <asm/page.h>
 #include <asm/memtype.h>

fs/namei.c

@@ -17,8 +17,8 @@
 
 #include <linux/init.h>
 #include <linux/export.h>
-#include <linux/kernel.h>
 #include <linux/slab.h>
+#include <linux/wordpart.h>
 #include <linux/fs.h>
 #include <linux/filelock.h>
 #include <linux/namei.h>

include/asm-generic/word-at-a-time.h

@@ -2,7 +2,8 @@
 #ifndef _ASM_WORD_AT_A_TIME_H
 #define _ASM_WORD_AT_A_TIME_H
 
-#include <linux/kernel.h>
+#include <linux/bitops.h>
+#include <linux/wordpart.h>
 #include <asm/byteorder.h>
 
 #ifdef __BIG_ENDIAN

include/linux/kernel.h

@@ -39,14 +39,6 @@
 
 #define STACK_MAGIC	0xdeadbeef
 
-/**
- * REPEAT_BYTE - repeat the value @x multiple times as an unsigned long value
- * @x: value to repeat
- *
- * NOTE: @x is not checked for > 0xff; larger values produce odd results.
- */
-#define REPEAT_BYTE(x)	((~0ul / 0xff) * (x))
-
 /* generic data direction definitions */
 #define READ			0
 #define WRITE			1

include/linux/wordpart.h

@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _LINUX_WORDPART_H
+#define _LINUX_WORDPART_H
+/**
+ * REPEAT_BYTE - repeat the value @x multiple times as an unsigned long value
+ * @x: value to repeat
+ *
+ * NOTE: @x is not checked for > 0xff; larger values produce odd results.
+ */
+#define REPEAT_BYTE(x)	((~0ul / 0xff) * (x))
+
+#endif // _LINUX_WORDPART_H