Index: lib/libc/sys/_umtx_op.2
===================================================================
--- lib/libc/sys/_umtx_op.2
+++ lib/libc/sys/_umtx_op.2
@@ -28,7 +28,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd November 16, 2020
+.Dd November 23, 2020
 .Dt _UMTX_OP 2
 .Os
 .Sh NAME
@@ -1272,6 +1272,28 @@
 .Sx ROBUST UMUTEXES
 subsection for details.
 .El
+.Pp
+The
+.Fa op
+argument may be a bitwise OR of a single command from above with one or more of
+the following flags:
+.Bl -tag -width indent
+.It Dv UMTX_OP__I386
+Request i386 ABI compatibility from the native
+.Nm
+system call.
+.Dv UMTX_OP__32BIT
+has no effect if this flag is set.
+This flag is valid for all architectures, but it is ignored on i386.
+.It Dv UMTX_OP__32BIT
+Request non-i386, 32-bit ABI compatibility from the native
+.Nm
+system call.
+This flag has no effect if
+.Dv UMTX_OP__I386
+is set.
+This flag is valid for all architectures.
+.El
 .Sh RETURN VALUES
 If successful,
 all requests, except
Index: lib/libsysdecode/flags.c
===================================================================
--- lib/libsysdecode/flags.c
+++ lib/libsysdecode/flags.c
@@ -941,6 +941,20 @@
 	return (lookup_value(umtxop, op));
 }
 
+bool
+sysdecode_umtx_op_flags(FILE *fp, int op, int *rem)
+{
+	uintmax_t val;
+	bool printed;
+
+	printed = false;
+	val = (unsigned)op;
+	print_mask_part(fp, umtxopflags, &val, &printed);
+	if (rem != NULL)
+		*rem = val;
+	return (printed);
+}
+
 const char *
 sysdecode_vmresult(int result)
 {
Index: lib/libsysdecode/mktables
===================================================================
--- lib/libsysdecode/mktables
+++ lib/libsysdecode/mktables
@@ -145,7 +145,8 @@
 gen_table "sockoptudplite"  "UDPLITE_[[:alnum:]_]+[[:space:]]+[0-9]+"      "netinet/udplite.h"
 gen_table "socktype"        "SOCK_[A-Z]+[[:space:]]+[1-9]+[0-9]*"          "sys/socket.h"
 gen_table "thrcreateflags"  "THR_[A-Z]+[[:space:]]+0x[0-9]+"               "sys/thr.h"
-gen_table "umtxop"          "UMTX_OP_[[:alnum:]_]+[[:space:]]+[0-9]+"      "sys/umtx.h"
+gen_table "umtxop"          "UMTX_OP_[[:alnum:]][[:alnum:]_]*[[:space:]]+[0-9]+"      "sys/umtx.h"
+gen_table "umtxopflags"     "UMTX_OP__[[:alnum:]_]+[[:space:]]+[0-9]+"                "sys/umtx.h"
 gen_table "vmprot"          "VM_PROT_[A-Z]+[[:space:]]+\(\(vm_prot_t\)[[:space:]]+0x[0-9]+\)"  "vm/vm.h"
 gen_table "vmresult"        "KERN_[A-Z_]+[[:space:]]+[0-9]+"               "vm/vm_param.h"
 gen_table "wait6opt"        "W[A-Z]+[[:space:]]+[0-9]+"                    "sys/wait.h"
Index: lib/libsysdecode/sysdecode.h
===================================================================
--- lib/libsysdecode/sysdecode.h
+++ lib/libsysdecode/sysdecode.h
@@ -121,6 +121,7 @@
 bool	sysdecode_thr_create_flags(FILE *_fp, int _flags, int *_rem);
 bool	sysdecode_umtx_cvwait_flags(FILE *_fp, u_long _flags, u_long *_rem);
 const char *sysdecode_umtx_op(int _op);
+bool	sysdecode_umtx_op_flags(FILE *_fp, int op, int *_rem);
 bool	sysdecode_umtx_rwlock_flags(FILE *_fp, u_long _flags, u_long *_rem);
 int	sysdecode_utrace(FILE *_fp, void *_buf, size_t _len);
 bool	sysdecode_vmprot(FILE *_fp, int _type, int *_rem);
Index: usr.bin/kdump/kdump.c
===================================================================
--- usr.bin/kdump/kdump.c
+++ usr.bin/kdump/kdump.c
@@ -254,14 +254,21 @@
 	}
 }
 
+static bool
+print_mask_arg_part(bool (*decoder)(FILE *, int, int *), int value, int *rem)
+{
+
+	printf("%#x<", value);
+	return (decoder(stdout, value, rem));
+}
+
 static void
 print_mask_arg(bool (*decoder)(FILE *, int, int *), int value)
 {
 	bool invalid;
 	int rem;
 
-	printf("%#x<", value);
-	invalid = !decoder(stdout, value, &rem);
+	invalid = !print_mask_arg_part(decoder, value, &rem);
 	printf(">");
 	if (invalid)
 		printf("<invalid>%u", rem);
@@ -1455,10 +1462,16 @@
 				ip++;
 				narg--;
 				break;
-			case SYS__umtx_op:
+			case SYS__umtx_op: {
+				int op;
+
 				print_number(ip, narg, c);
 				putchar(',');
-				print_integer_arg(sysdecode_umtx_op, *ip);
+				if (print_mask_arg_part(sysdecode_umtx_op_flags,
+				    *ip, &op))
+					putchar('|');
+				print_integer_arg(sysdecode_umtx_op, op);
+				putchar('>');
 				switch (*ip) {
 				case UMTX_OP_CV_WAIT:
 					ip++;
@@ -1478,6 +1491,7 @@
 				ip++;
 				narg--;
 				break;
+			}
 			case SYS_ftruncate:
 			case SYS_truncate:
 				print_number(ip, narg, c);
Index: usr.bin/truss/syscalls.c
===================================================================
--- usr.bin/truss/syscalls.c
+++ usr.bin/truss/syscalls.c
@@ -888,12 +888,20 @@
 		fprintf(fp, "%d", value);
 }
 
+static bool
+print_mask_arg_part(bool (*decoder)(FILE *, int, int *), FILE *fp, int value,
+    int *rem)
+{
+
+	return (decoder(fp, value, rem));
+}
+
 static void
 print_mask_arg(bool (*decoder)(FILE *, int, int *), FILE *fp, int value)
 {
 	int rem;
 
-	if (!decoder(fp, value, &rem))
+	if (!print_mask_arg_part(decoder, fp, value, &rem))
 		fprintf(fp, "0x%x", rem);
 	else if (rem != 0)
 		fprintf(fp, "|0x%x", rem);
@@ -2303,9 +2311,15 @@
 	case Procctl:
 		print_integer_arg(sysdecode_procctl_cmd, fp, args[sc->offset]);
 		break;
-	case Umtxop:
-		print_integer_arg(sysdecode_umtx_op, fp, args[sc->offset]);
+	case Umtxop: {
+		int rem;
+
+		if (print_mask_arg_part(sysdecode_umtx_op_flags, fp,
+		    args[sc->offset], &rem))
+			fprintf(fp, "|");
+		print_integer_arg(sysdecode_umtx_op, fp, rem);
 		break;
+	}
 	case Atfd:
 		print_integer_arg(sysdecode_atfd, fp, args[sc->offset]);
 		break;