x86, boot: Move memcmp() into string.h and string.c

Try to treat memcmp() in same way as memcpy() and memset(). Provide a
declaration in boot/string.h and by default user gets a memcmp() which
maps to builtin function.

Move optimized definition of memcmp() in boot/string.c. Now a user can
do #undef memcmp and link against string.c to use optimzied memcmp().

It also simplifies boot/compressed/string.c where we had to redefine
memcmp(). That extra definition is gone now.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Link: http://lkml.kernel.org/r/1395170800-11059-5-git-send-email-vgoyal@redhat.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

1 files changed, 14 insertions, 0 deletions

diff --git a/arch/x86/boot/string.c b/arch/x86/boot/string.c
index 574dedfe2890..5339040ef86e 100644
--- a/arch/x86/boot/string.c
+++ b/arch/x86/boot/string.c
@@ -14,6 +14,20 @@
 
 #include "boot.h"
 
+/*
+ * This file gets included in compressed/string.c which might pull in
+ * string_32.h and which in turn maps memcmp to __builtin_memcmp(). Undo
+ * that first.
+ */
+#undef memcmp
+int memcmp(const void *s1, const void *s2, size_t len)
+{
+	u8 diff;
+	asm("repe; cmpsb; setnz %0"
+	    : "=qm" (diff), "+D" (s1), "+S" (s2), "+c" (len));
+	return diff;
+}
+
 int strcmp(const char *str1, const char *str2)
 {
 	const unsigned char *s1 = (const unsigned char *)str1;