[PATCH v2 1/3] x86/asm, x86/boot: Expose inline memcmp

[Mauricio Faria de Oliveira <mfo@igalia.com>]

Move the inline memcmp function, currently only available to boot code
(boot/string.c), into the header with similar inline string functions
(include/asm/string.h) so it may be reused.

Add a _SETUP guard in string.h so not to include the 32/64-bit specific
string headers in boot/ code (16-bit, real mode) and avoid build errors.

Note: this memcmp() only returns 0/1, not -1/0/1 as regular memcmp(),
as reported by David Laight. This should be addressed separately.

Signed-off-by: Mauricio Faria de Oliveira <mfo@igalia.com>
---
 arch/x86/boot/string.c        |  6 ++----
 arch/x86/include/asm/string.h | 12 ++++++++++++
 2 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/arch/x86/boot/string.c b/arch/x86/boot/string.c
index b25c6a9303b7314d5caf5c9306239811705294fe..bbee78637b349e42e9281d8df50d89d48f4490b9 100644
--- a/arch/x86/boot/string.c
+++ b/arch/x86/boot/string.c
@@ -15,6 +15,7 @@
 #include <linux/errno.h>
 #include <linux/limits.h>
 #include <asm/asm.h>
+#include <asm/string.h>
 #include "ctype.h"
 #include "string.h"
 
@@ -31,10 +32,7 @@
 
 int memcmp(const void *s1, const void *s2, size_t len)
 {
-	bool diff;
-	asm("repe cmpsb"
-	    : "=@ccnz" (diff), "+D" (s1), "+S" (s2), "+c" (len));
-	return diff;
+	return __inline_memcmp(s1, s2, len);
 }
 
 /*
diff --git a/arch/x86/include/asm/string.h b/arch/x86/include/asm/string.h
index 9cb5aae7fba9ffcf0f5af8f939d30467750ccaa9..ae6c1f4fda858bd8370647557529d98c23305a53 100644
--- a/arch/x86/include/asm/string.h
+++ b/arch/x86/include/asm/string.h
@@ -2,11 +2,13 @@
 #ifndef _ASM_X86_STRING_H
 #define _ASM_X86_STRING_H
 
+#ifndef _SETUP
 #ifdef CONFIG_X86_32
 # include <asm/string_32.h>
 #else
 # include <asm/string_64.h>
 #endif
+#endif
 
 static __always_inline void *__inline_memcpy(void *to, const void *from, size_t len)
 {
@@ -29,4 +31,14 @@ static __always_inline void *__inline_memset(void *s, int v, size_t n)
 	return ret;
 }
 
+/* Note: this memcmp() only returns 0/1, not -1/0/1 as regular memcmp(). */
+static __always_inline int __inline_memcmp(const void *s1, const void *s2, size_t len)
+{
+	bool diff;
+
+	asm("repe cmpsb"
+	    : "=@ccnz" (diff), "+D" (s1), "+S" (s2), "+c" (len));
+	return diff;
+}
+
 #endif /* _ASM_X86_STRING_H */

-- 
2.51.0