Index: sys/net/iflib.h
===================================================================
--- sys/net/iflib.h
+++ sys/net/iflib.h
@@ -248,7 +248,7 @@
 
 	/* fields necessary for probe */
 	pci_vendor_info_t *isc_vendor_info;
-	char *isc_driver_version;
+	const char *isc_driver_version;
 	/* optional function to transform the read values to match the table*/
 	void (*isc_parse_devinfo) (uint16_t *device_id, uint16_t *subvendor_id,
 				   uint16_t *subdevice_id, uint16_t *rev_id);
Index: sys/sys/cdefs.h
===================================================================
--- sys/sys/cdefs.h
+++ sys/sys/cdefs.h
@@ -801,6 +801,23 @@
 #define	__NULLABILITY_PRAGMA_POP _Pragma("clang diagnostic pop")
 #endif
 
+/*
+ * ignore -Wincompatible-pointer-types-discards-qualifiers warnings
+ * caused by assigning a const pointer to a non-const storage.
+ *
+ * Usage:
+ *   __drop_const(storage = val);
+ */
+#if !defined(__clang__)
+#define __drop_const(expr) (expr)
+#else
+#define __drop_const(expr) \
+	_Pragma("clang diagnostic push") \
+	_Pragma("clang diagnostic ignored \"-Wincompatible-pointer-types-discards-qualifiers\"") \
+	(expr) \
+	_Pragma("clang diagnostic push")
+#endif
+
 /*
  * Type Safety Checking
  *
Index: sys/sys/sysctl.h
===================================================================
--- sys/sys/sysctl.h
+++ sys/sys/sysctl.h
@@ -346,7 +346,10 @@
 
 #define	SYSCTL_ADD_STRING(ctx, parent, nbr, name, access, arg, len, descr) \
 ({									\
-	char *__arg = (arg);						\
+	char *__arg;							\
+	__builtin_choose_expr(__builtin_constant_p(arg),		\
+			      __drop_const(__arg = (arg)),		\
+			      __arg = (arg));				\
 	CTASSERT(((access) & CTLTYPE) == 0 ||				\
 	    ((access) & SYSCTL_CT_ASSERT_MASK) == CTLTYPE_STRING);	\
 	sysctl_add_oid(ctx, parent, nbr, name, CTLTYPE_STRING|(access),	\