[PATCH v3 2/4] x86/asm, x86/boot: expose inline memcmp

[Mauricio Faria de Oliveira <mfo@xxxxxxxxxx>]

Move the inline memcmp function currently only available in 'boot/string.c'
and its users (eg, 'boot/compressed/string.c' and 'purgatory/purgatory.ro')
into the inline string functions header <asm/string_inline.h> to be reused.

Note that the inline memcmp() returns 0/1, not -1/0/1 as regular memcmp()
(reported by David Laight <david.laight.linux@xxxxxxxxx>), which is not
caused or changed by this commit; this will be addressed separately.

Signed-off-by: Mauricio Faria de Oliveira <mfo@xxxxxxxxxx>
---
 arch/x86/boot/string.c               |  6 ++----
 arch/x86/include/asm/string_inline.h | 11 +++++++++++
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/arch/x86/boot/string.c b/arch/x86/boot/string.c
index 
ac0f900ebc47efa81c92e1bb2010ea41677899c4..544681d046c3f87101309ffaca0c90512a244856
 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_inline.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_inline.h 
b/arch/x86/include/asm/string_inline.h
index 
ffcfa6583d2bc7b91d078888518d0e80248af940..91ed89bfdfa9b148002441e94f48039b17f70391
 100644
--- a/arch/x86/include/asm/string_inline.h
+++ b/arch/x86/include/asm/string_inline.h
@@ -23,4 +23,15 @@ static __always_inline void *__inline_memset(void *s, int v, 
size_t n)
        return ret;
 }
 
+/* Note: this memcmp() 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_INLINE_H */

-- 
2.51.0