Index: lib/libc/gen/sysctl.3
===================================================================
--- lib/libc/gen/sysctl.3
+++ lib/libc/gen/sysctl.3
@@ -865,6 +865,9 @@
 The
 .Fa name
 array specifies a value that is unknown.
+.It Bq Er ENXIO
+The associated kernel variable has gotten a bad value and
+no sensible result is available.
 .It Bq Er EPERM
 An attempt is made to set a read-only value.
 .It Bq Er EPERM
Index: sys/kern/subr_param.c
===================================================================
--- sys/kern/subr_param.c
+++ sys/kern/subr_param.c
@@ -80,7 +80,15 @@
 #define	MAXFILES (40 + 32 * maxusers)
 #endif
 
-static int sysctl_kern_vm_guest(SYSCTL_HANDLER_ARGS);
+struct sysctl_enum_params {
+	int *const value;
+	int first;
+	u_int count;
+	char *const names[];
+};
+
+static int sysctl_enum_proc(struct sysctl_oid *oidp, void *const _params,
+	intmax_t arg2, struct sysctl_req *req);
 
 int	hz;				/* system clock's frequency */
 int	tick;				/* usec per tick (1000000 / hz) */
@@ -136,28 +144,32 @@
     "Maximum stack size");
 SYSCTL_ULONG(_kern, OID_AUTO, sgrowsiz, CTLFLAG_RWTUN | CTLFLAG_NOFETCH, &sgrowsiz, 0,
     "Amount to grow stack on a stack fault");
-SYSCTL_PROC(_kern, OID_AUTO, vm_guest,
-    CTLFLAG_RD | CTLTYPE_STRING | CTLFLAG_MPSAFE, NULL, 0,
-    sysctl_kern_vm_guest, "A",
-    "Virtual machine guest detected?");
 
 /*
- * The elements of this array are ordered based upon the values of the
- * corresponding enum VM_GUEST members.
+ * Parameters for the vm_guest enum
  */
-static const char *const vm_guest_sysctl_names[] = {
-	[VM_GUEST_NO] = "none",
-	[VM_GUEST_VM] = "generic",
-	[VM_GUEST_XEN] = "xen",
-	[VM_GUEST_HV] = "hv",
-	[VM_GUEST_VMWARE] = "vmware",
-	[VM_GUEST_KVM] = "kvm",
-	[VM_GUEST_BHYVE] = "bhyve",
-	[VM_GUEST_VBOX] = "vbox",
-	[VM_GUEST_PARALLELS] = "parallels",
-	[VM_LAST] = NULL
+static const struct sysctl_enum_params vm_guest_sysctl_params = {
+	&vm_guest,
+	VM_GUEST_NO,
+	VM_LAST - VM_GUEST_NO, /* VM_LAST is an invalid value */
+	{
+		[VM_GUEST_BHYVE		- VM_GUEST_NO] = "bhyve",
+		[VM_GUEST_HV		- VM_GUEST_NO] = "hv",
+		[VM_GUEST_KVM		- VM_GUEST_NO] = "kvm",
+		[VM_GUEST_NO		- VM_GUEST_NO] = "none",
+		[VM_GUEST_PARALLELS	- VM_GUEST_NO] = "parallels",
+		[VM_GUEST_VBOX		- VM_GUEST_NO] = "vbox",
+		[VM_GUEST_VM		- VM_GUEST_NO] = "generic",
+		[VM_GUEST_VMWARE	- VM_GUEST_NO] = "vmware",
+		[VM_GUEST_XEN		- VM_GUEST_NO] = "xen",
+		[VM_LAST		- VM_GUEST_NO] = NULL
+	}
 };
-CTASSERT(nitems(vm_guest_sysctl_names) - 1 == VM_LAST);
+
+SYSCTL_PROC(_kern, OID_AUTO, vm_guest,
+    CTLFLAG_RD | CTLTYPE_STRING | CTLFLAG_MPSAFE,
+    __DECONST(void *, &vm_guest_sysctl_params), 0, sysctl_enum_proc, "A",
+    "Virtual machine guest detected?");
 
 /*
  * Boot time overrides that are not scaled against main memory
@@ -325,10 +337,18 @@
 }
 
 /*
- * Sysctl stringifying handler for kern.vm_guest.
+ * Generalized sysctl stringifying handler for enums
  */
 static int
-sysctl_kern_vm_guest(SYSCTL_HANDLER_ARGS)
+sysctl_enum_proc(struct sysctl_oid *oidp, void *const _params,
+    intmax_t arg2, struct sysctl_req *req)
 {
-	return (SYSCTL_OUT_STR(req, vm_guest_sysctl_names[vm_guest]));
+	const struct sysctl_enum_params *const params = _params;
+	u_int index = *params->value - params->first;
+
+	if (index >= params->count)
+		return (ENXIO);
+	if (params->names[index] == NULL)
+		return (0);
+	return (SYSCTL_OUT_STR(req, params->names[index]));
 }