2 files changed, 60 insertions, 1 deletions

diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile
index 965026472c71..a2d6472895fb 100644
--- a/arch/x86/lib/Makefile
+++ b/arch/x86/lib/Makefile
@@ -29,7 +29,9 @@ ifeq ($(CONFIG_X86_32),y)
         lib-y += checksum_32.o
         lib-y += strstr_32.o
         lib-y += semaphore_32.o string_32.o
-
+ifneq ($(CONFIG_X86_CMPXCHG64),y)
+        lib-y += cmpxchg8b_emu.o
+endif
         lib-$(CONFIG_X86_USE_3DNOW) += mmx_32.o
 else
         obj-y += io_64.o iomap_copy_64.o
diff --git a/arch/x86/lib/cmpxchg8b_emu.S b/arch/x86/lib/cmpxchg8b_emu.S
new file mode 100644
index 000000000000..828cb710dec2
--- /dev/null
+++ b/arch/x86/lib/cmpxchg8b_emu.S
@@ -0,0 +1,57 @@
+/*
+ *      This program is free software; you can redistribute it and/or
+ *      modify it under the terms of the GNU General Public License
+ *      as published by the Free Software Foundation; version 2
+ *      of the License.
+ *
+ */
+
+#include <linux/linkage.h>
+#include <asm/alternative-asm.h>
+#include <asm/frame.h>
+#include <asm/dwarf2.h>
+
+
+.text
+
+/*
+ * Inputs:
+ * %esi : memory location to compare
+ * %eax : low 32 bits of old value
+ * %edx : high 32 bits of old value
+ * %ebx : low 32 bits of new value
+ * %ecx : high 32 bits of new value
+ */
+ENTRY(cmpxchg8b_emu)
+CFI_STARTPROC
+
+#
+# Emulate 'cmpxchg8b (%esi)' on UP except we don't
+# set the whole ZF thing (caller will just compare
+# eax:edx with the expected value)
+#
+cmpxchg8b_emu:
+        pushfl
+        cli
+
+        cmpl  (%esi), %eax
+        jne not_same
+        cmpl 4(%esi), %edx
+        jne half_same
+
+        movl %ebx,  (%esi)
+        movl %ecx, 4(%esi)
+
+        popfl
+        ret
+
+ not_same:
+        movl  (%esi), %eax
+ half_same:
+        movl 4(%esi), %edx
+
+        popfl
+        ret
+
+CFI_ENDPROC
+ENDPROC(cmpxchg8b_emu)