Index: sys/compat/freebsd32/freebsd32_misc.c
===================================================================
--- sys/compat/freebsd32/freebsd32_misc.c
+++ sys/compat/freebsd32/freebsd32_misc.c
@@ -3310,13 +3310,73 @@
 	    PAIR32TO64(id_t, uap->id), uap->setid));
 }
 
+static int
+copyin32_set(struct thread *td, const void *u, void *k, size_t size)
+{
+#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+	int rv;
+	struct bitset *kb = k;
+	int *p;
+
+	rv = copyin(u, k, size);
+
+	if (rv != 0)
+		return (rv);
+
+	p = (int *)kb->__bits;
+	/* Loop through swapping words. */
+	/* `size' is in bytes, we need bits. */
+	for (int i = 0; i < __bitset_words(size * 8); i++) {
+		int tmp = p[0];
+		p[0] = p[1];
+		p[1] = tmp;
+		p += 2;
+	}
+	return (rv);
+#else
+	return (copyin(u, k, size));
+#endif
+}
+
+static int
+copyout32_set(struct thread *td, const void *k, void *u, size_t size)
+{
+#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+	const struct bitset *kb = k;
+	struct bitset *ub = u;
+	const int *kp = (const int *)kb->__bits;
+	int *up = (int *)ub->__bits;
+	int rv;
+
+	for (int i = 0; i < __bitset_words(CPU_SETSIZE); i++) {
+		/* `size' is in bytes, we need bits. */
+		for (int i = 0; i < __bitset_words(size * 8); i++) {
+			rv = suword32(up, kp[1]);
+			if (rv == 0)
+				rv = suword32(up + 1, kp[0]);
+			if (rv != 0)
+				return (rv);
+		}
+	}
+	return (0);
+#else
+	return (copyout(k, u, size));
+#endif
+}
+
+struct cpuset_copy_cb cpuset_copy32_cb = {
+	.copyin = copyin32_set,
+	.copyout = copyout32_set
+};
+
 int
 freebsd32_cpuset_getaffinity(struct thread *td,
     struct freebsd32_cpuset_getaffinity_args *uap)
 {
 
 	return (kern_cpuset_getaffinity(td, uap->level, uap->which,
-	    PAIR32TO64(id_t,uap->id), uap->cpusetsize, uap->mask));
+	    PAIR32TO64(id_t,uap->id), uap->cpusetsize, uap->mask,
+	    &cpuset_copy32_cb));
 }
 
 int
@@ -3325,7 +3385,8 @@
 {
 
 	return (user_cpuset_setaffinity(td, uap->level, uap->which,
-	    PAIR32TO64(id_t,uap->id), uap->cpusetsize, uap->mask));
+	    PAIR32TO64(id_t,uap->id), uap->cpusetsize, uap->mask,
+	    &cpuset_copy32_cb));
 }
 
 int
@@ -3334,7 +3395,8 @@
 {
 
 	return (kern_cpuset_getdomain(td, uap->level, uap->which,
-	    PAIR32TO64(id_t,uap->id), uap->domainsetsize, uap->mask, uap->policy));
+	    PAIR32TO64(id_t,uap->id), uap->domainsetsize, uap->mask, uap->policy,
+	    &cpuset_copy32_cb));
 }
 
 int
@@ -3343,7 +3405,8 @@
 {
 
 	return (kern_cpuset_setdomain(td, uap->level, uap->which,
-	    PAIR32TO64(id_t,uap->id), uap->domainsetsize, uap->mask, uap->policy));
+	    PAIR32TO64(id_t,uap->id), uap->domainsetsize, uap->mask, uap->policy,
+	    &cpuset_copy32_cb));
 }
 
 int
Index: sys/kern/kern_cpuset.c
===================================================================
--- sys/kern/kern_cpuset.c
+++ sys/kern/kern_cpuset.c
@@ -52,6 +52,7 @@
 #include <sys/sched.h>
 #include <sys/smp.h>
 #include <sys/syscallsubr.h>
+#include <sys/sysent.h>
 #include <sys/capsicum.h>
 #include <sys/cpuset.h>
 #include <sys/domainset.h>
@@ -1742,6 +1743,23 @@
 	return (0);
 }
 
+static int
+copyin_set(struct thread *td, const void *u, void *k, size_t size)
+{
+	return (copyin(u, k, size));
+}
+
+static int
+copyout_set(struct thread *td, const void *k, void *u, size_t size)
+{
+	return (copyout(k, u, size));
+}
+
+static struct cpuset_copy_cb copy_set = {
+	.copyin = copyin_set,
+	.copyout = copyout_set
+};
+
 #ifndef _SYS_SYSPROTO_H_
 struct cpuset_args {
 	cpusetid_t	*setid;
@@ -1883,12 +1901,12 @@
 {
 
 	return (kern_cpuset_getaffinity(td, uap->level, uap->which,
-	    uap->id, uap->cpusetsize, uap->mask));
+	    uap->id, uap->cpusetsize, uap->mask, &copy_set));
 }
 
 int
 kern_cpuset_getaffinity(struct thread *td, cpulevel_t level, cpuwhich_t which,
-    id_t id, size_t cpusetsize, cpuset_t *maskp)
+    id_t id, size_t cpusetsize, cpuset_t *maskp, struct cpuset_copy_cb *cb)
 {
 	struct thread *ttd;
 	struct cpuset *nset;
@@ -1977,7 +1995,7 @@
 			goto out;
 		}
 		size = min(cpusetsize, sizeof(cpuset_t));
-		error = copyout(mask, maskp, size);
+		error = cb->copyout(td, mask, maskp, size);
 		if (error != 0)
 			goto out;
 		if (cpusetsize > size) {
@@ -2021,7 +2039,7 @@
 {
 
 	return (user_cpuset_setaffinity(td, uap->level, uap->which,
-	    uap->id, uap->cpusetsize, uap->mask));
+	    uap->id, uap->cpusetsize, uap->mask, &copy_set));
 }
 
 int
@@ -2109,7 +2127,7 @@
 
 int
 user_cpuset_setaffinity(struct thread *td, cpulevel_t level, cpuwhich_t which,
-    id_t id, size_t cpusetsize, const cpuset_t *maskp)
+    id_t id, size_t cpusetsize, const cpuset_t *maskp, struct cpuset_copy_cb *cb)
 {
 	cpuset_t *mask;
 	int error;
@@ -2117,7 +2135,7 @@
 
 	size = min(cpusetsize, sizeof(cpuset_t));
 	mask = malloc(sizeof(cpuset_t), M_TEMP, M_WAITOK | M_ZERO);
-	error = copyin(maskp, mask, size);
+	error = cb->copyin(td, maskp, mask, size);
 	if (error)
 		goto out;
 	/*
@@ -2165,12 +2183,13 @@
 {
 
 	return (kern_cpuset_getdomain(td, uap->level, uap->which,
-	    uap->id, uap->domainsetsize, uap->mask, uap->policy));
+	    uap->id, uap->domainsetsize, uap->mask, uap->policy, &copy_set));
 }
 
 int
 kern_cpuset_getdomain(struct thread *td, cpulevel_t level, cpuwhich_t which,
-    id_t id, size_t domainsetsize, domainset_t *maskp, int *policyp)
+    id_t id, size_t domainsetsize, domainset_t *maskp, int *policyp,
+    struct cpuset_copy_cb *cb)
 {
 	struct domainset outset;
 	struct thread *ttd;
@@ -2268,7 +2287,7 @@
 	}
 	DOMAINSET_COPY(&outset.ds_mask, mask);
 	if (error == 0)
-		error = copyout(mask, maskp, domainsetsize);
+		error = cb->copyout(td, mask, maskp, domainsetsize);
 	if (error == 0)
 		if (suword32(policyp, outset.ds_policy) != 0)
 			error = EFAULT;
@@ -2292,12 +2311,13 @@
 {
 
 	return (kern_cpuset_setdomain(td, uap->level, uap->which,
-	    uap->id, uap->domainsetsize, uap->mask, uap->policy));
+	    uap->id, uap->domainsetsize, uap->mask, uap->policy, &copy_set));
 }
 
 int
 kern_cpuset_setdomain(struct thread *td, cpulevel_t level, cpuwhich_t which,
-    id_t id, size_t domainsetsize, const domainset_t *maskp, int policy)
+    id_t id, size_t domainsetsize, const domainset_t *maskp, int policy,
+    struct cpuset_copy_cb *cb)
 {
 	struct cpuset *nset;
 	struct cpuset *set;
@@ -2318,7 +2338,7 @@
 		return (error);
 	memset(&domain, 0, sizeof(domain));
 	mask = malloc(domainsetsize, M_TEMP, M_WAITOK | M_ZERO);
-	error = copyin(maskp, mask, domainsetsize);
+	error = cb->copyin(td, maskp, mask, domainsetsize);
 	if (error)
 		goto out;
 	/*
Index: sys/sys/cpuset.h
===================================================================
--- sys/sys/cpuset.h
+++ sys/sys/cpuset.h
@@ -154,6 +154,15 @@
 struct proc;
 struct thread;
 
+/*
+ * Callbacks for copying in/out a cpuset or domainset.  Used for alternate
+ * ABIs, like compat32.
+ */
+struct cpuset_copy_cb {
+	int (*copyin)(struct thread *, const void *, void *, size_t);
+	int (*copyout)(struct thread *, const void *, void *, size_t);
+};
+
 struct cpuset *cpuset_thread0(void);
 struct cpuset *cpuset_ref(struct cpuset *);
 void	cpuset_rel(struct cpuset *);
Index: sys/sys/syscallsubr.h
===================================================================
--- sys/sys/syscallsubr.h
+++ sys/sys/syscallsubr.h
@@ -39,6 +39,7 @@
 #include <sys/_uio.h>
 
 struct __wrusage;
+struct cpuset_copy_cb;
 struct file;
 struct filecaps;
 enum idtype;
@@ -119,18 +120,19 @@
 int	kern_copy_file_range(struct thread *td, int infd, off_t *inoffp,
 	    int outfd, off_t *outoffp, size_t len, unsigned int flags);
 int	kern_cpuset_getaffinity(struct thread *td, cpulevel_t level,
-	    cpuwhich_t which, id_t id, size_t cpusetsize, cpuset_t *maskp);
+	    cpuwhich_t which, id_t id, size_t cpusetsize, cpuset_t *maskp,
+	    struct cpuset_copy_cb *cb);
 int	kern_cpuset_setaffinity(struct thread *td, cpulevel_t level,
 	    cpuwhich_t which, id_t id, cpuset_t *maskp);
 int	user_cpuset_setaffinity(struct thread *td, cpulevel_t level,
 	    cpuwhich_t which, id_t id, size_t cpusetsize,
-	    const cpuset_t *maskp);
+	    const cpuset_t *maskp, struct cpuset_copy_cb *cb);
 int	kern_cpuset_getdomain(struct thread *td, cpulevel_t level,
 	    cpuwhich_t which, id_t id, size_t domainsetsize,
-	    domainset_t *maskp, int *policyp);
+	    domainset_t *maskp, int *policyp, struct cpuset_copy_cb *cb);
 int	kern_cpuset_setdomain(struct thread *td, cpulevel_t level,
 	    cpuwhich_t which, id_t id, size_t domainsetsize,
-	    const domainset_t *maskp, int policy);
+	    const domainset_t *maskp, int policy, struct cpuset_copy_cb *cb);
 int	kern_cpuset_getid(struct thread *td, cpulevel_t level,
 	    cpuwhich_t which, id_t id, cpusetid_t *setid);
 int	kern_cpuset_setid(struct thread *td, cpuwhich_t which,