--- Modules/_ctypes/libffi_osx/x86/x86-ffi64.c
+++ Modules/_ctypes/libffi_osx/x86/x86-ffi64.c
@@ -599,9 +599,15 @@
 	tramp = (volatile unsigned short*)&closure->tramp[0];
 
 	tramp[0] = 0xbb49;		/* mov <code>, %r11	*/
-	*(void* volatile*)&tramp[1] = ffi_closure_unix64;
+	tramp[1] = (unsigned short) ffi_closure_unix64;
+	tramp[2] = (unsigned short) (((unsigned long)ffi_closure_unix64) >> 16);
+	tramp[3] = (unsigned short) (((unsigned long)ffi_closure_unix64) >> 32);
+	tramp[4] = (unsigned short) (((unsigned long)ffi_closure_unix64) >> 48);
 	tramp[5] = 0xba49;		/* mov <data>, %r10	*/
-	*(void* volatile*)&tramp[6] = closure;
+	tramp[6] = (unsigned short) closure;
+	tramp[7] = (unsigned short) (((unsigned long)closure) >> 16);
+	tramp[8] = (unsigned short) (((unsigned long)closure) >> 32);
+	tramp[9] = (unsigned short) (((unsigned long)closure) >> 48);
 
 	/*	Set the carry bit if the function uses any sse registers.
 		This is clc or stc, together with the first byte of the jmp.  */
--- Modules/posixmodule.c
+++ Modules/posixmodule.c
@@ -23,6 +23,9 @@
 };
 
 static int
+#if defined __clang__
+__attribute__((no_sanitize("shift-base"))) // MFD_HUGE_16GB in /usr/include/linux/memfd.h
+#endif
 all_ins(PyObject *m)
 {
 #ifdef F_OK
--- Objects/listobject.c
+++ Objects/listobject.c
@@ -548,7 +548,7 @@
         dest[i] = v;
     }
     src = b->ob_item;
-    dest = np->ob_item + Py_SIZE(a);
+    dest = Py_SIZE(a) == 0 ? np->ob_item : np->ob_item + Py_SIZE(a);
     for (i = 0; i < Py_SIZE(b); i++) {
         PyObject *v = src[i];
         Py_INCREF(v);