1 files changed, 20 insertions, 0 deletions
diff --git a/lib/src/common.c b/lib/src/common.c
index 2d122f5..dd806bf 100644
--- a/lib/src/common.c
+++ b/lib/src/common.c
@@ -16,3 +16,23 @@ void* memset(void* s, int c, size_t n) {
         : "memory");
     return s;
 }
+
+void* memcpy(void* d, const void* s, size_t n) {
+    // When `d` points into `[s, s+n[` we would override `s` while copying into `d`.
+    //   |------------|--------|
+    //   s            d        s+n
+    // -> We don't support.
+    //
+    // When `d` points into `]s-n, s[` it is destructive for `s` but all data
+    // from `s` are copied into `d`. The user gets what he asks for.
+    // -> Supported.
+    ERROR_ON(s <= d && d < (void*)((unsigned char*)s + n), "memcpy: Unsupported overlap!");
+    asm volatile(
+        "cld"
+        "\n"
+        "rep movsb"
+        : "+D"(d), "+S"(s), "+c"(n)
+        :
+        : "memory");
+    return d;
+}