v4.19.13 snapshot.
diff --git a/arch/x86/boot/compressed/string.c b/arch/x86/boot/compressed/string.c
new file mode 100644
index 0000000..19dbbcd
--- /dev/null
+++ b/arch/x86/boot/compressed/string.c
@@ -0,0 +1,75 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * This provides an optimized implementation of memcpy, and a simplified
+ * implementation of memset and memmove. These are used here because the
+ * standard kernel runtime versions are not yet available and we don't
+ * trust the gcc built-in implementations as they may do unexpected things
+ * (e.g. FPU ops) in the minimal decompression stub execution environment.
+ */
+#include "error.h"
+
+#include "../string.c"
+
+#ifdef CONFIG_X86_32
+static void *__memcpy(void *dest, const void *src, size_t n)
+{
+ int d0, d1, d2;
+ asm volatile(
+ "rep ; movsl\n\t"
+ "movl %4,%%ecx\n\t"
+ "rep ; movsb\n\t"
+ : "=&c" (d0), "=&D" (d1), "=&S" (d2)
+ : "0" (n >> 2), "g" (n & 3), "1" (dest), "2" (src)
+ : "memory");
+
+ return dest;
+}
+#else
+static void *__memcpy(void *dest, const void *src, size_t n)
+{
+ long d0, d1, d2;
+ asm volatile(
+ "rep ; movsq\n\t"
+ "movq %4,%%rcx\n\t"
+ "rep ; movsb\n\t"
+ : "=&c" (d0), "=&D" (d1), "=&S" (d2)
+ : "0" (n >> 3), "g" (n & 7), "1" (dest), "2" (src)
+ : "memory");
+
+ return dest;
+}
+#endif
+
+void *memset(void *s, int c, size_t n)
+{
+ int i;
+ char *ss = s;
+
+ for (i = 0; i < n; i++)
+ ss[i] = c;
+ return s;
+}
+
+void *memmove(void *dest, const void *src, size_t n)
+{
+ unsigned char *d = dest;
+ const unsigned char *s = src;
+
+ if (d <= s || d - s >= n)
+ return __memcpy(dest, src, n);
+
+ while (n-- > 0)
+ d[n] = s[n];
+
+ return dest;
+}
+
+/* Detect and warn about potential overlaps, but handle them with memmove. */
+void *memcpy(void *dest, const void *src, size_t n)
+{
+ if (dest > src && dest - src < n) {
+ warn("Avoiding potentially unsafe overlapping memcpy()!");
+ return memmove(dest, src, n);
+ }
+ return __memcpy(dest, src, n);
+}