1 files changed, 46 insertions, 0 deletions
diff --git a/arch/x86/lib/cmpxchg8b_emu.S b/arch/x86/lib/cmpxchg8b_emu.S
new file mode 100644
index 000000000..6a912d58f
--- /dev/null
+++ b/arch/x86/lib/cmpxchg8b_emu.S
@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#include <linux/linkage.h>
+#include <asm/export.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
+ */
+SYM_FUNC_START(cmpxchg8b_emu)
+
+#
+# Emulate 'cmpxchg8b (%esi)' on UP except we don't
+# set the whole ZF thing (caller will just compare
+# eax:edx with the expected value)
+#
+	pushfl
+	cli
+
+	cmpl  (%esi), %eax
+	jne .Lnot_same
+	cmpl 4(%esi), %edx
+	jne .Lhalf_same
+
+	movl %ebx,  (%esi)
+	movl %ecx, 4(%esi)
+
+	popfl
+	RET
+
+.Lnot_same:
+	movl  (%esi), %eax
+.Lhalf_same:
+	movl 4(%esi), %edx
+
+	popfl
+	RET
+
+SYM_FUNC_END(cmpxchg8b_emu)
+EXPORT_SYMBOL(cmpxchg8b_emu)