diff --git a/src/android/net/apf/ApfFilter.java b/src/android/net/apf/ApfFilter.java
index 9a3d58b..cfd54bc 100644
--- a/src/android/net/apf/ApfFilter.java
+++ b/src/android/net/apf/ApfFilter.java
@@ -16,6 +16,8 @@
 
 package android.net.apf;
 
+import static android.net.apf.ApfV4Generator.Register.R0;
+import static android.net.apf.ApfV4Generator.Register.R1;
 import static android.net.util.SocketUtils.makePacketSocketAddress;
 import static android.os.PowerManager.ACTION_DEVICE_IDLE_MODE_CHANGED;
 import static android.os.PowerManager.ACTION_DEVICE_LIGHT_IDLE_MODE_CHANGED;
@@ -47,7 +49,6 @@
 import android.net.TcpKeepalivePacketDataParcelable;
 import android.net.apf.ApfCounterTracker.Counter;
 import android.net.apf.ApfV4Generator.IllegalInstructionException;
-import android.net.apf.ApfV4Generator.Register;
 import android.net.ip.IpClient.IpClientCallbacksWrapper;
 import android.os.PowerManager;
 import android.os.SystemClock;
@@ -141,7 +142,7 @@
      */
     private void maybeSetupCounter(ApfV4Generator gen, Counter c) {
         if (mApfCapabilities.hasDataAccess()) {
-            gen.addLoadImmediate(Register.R1, c.offset());
+            gen.addLoadImmediate(R1, c.offset());
         }
     }
 
@@ -1138,15 +1139,15 @@
                 throws IllegalInstructionException {
             String nextFilterLabel = "Ra" + getUniqueNumberLocked();
             // Skip if packet is not the right size
-            gen.addLoadFromMemory(Register.R0, gen.PACKET_SIZE_MEMORY_SLOT);
+            gen.addLoadFromMemory(R0, gen.PACKET_SIZE_MEMORY_SLOT);
             gen.addJumpIfR0NotEquals(mPacket.capacity(), nextFilterLabel);
             // Skip filter if expired
-            gen.addLoadFromMemory(Register.R0, gen.FILTER_AGE_MEMORY_SLOT);
+            gen.addLoadFromMemory(R0, gen.FILTER_AGE_MEMORY_SLOT);
             gen.addJumpIfR0GreaterThan(getRemainingFilterLft(timeSeconds), nextFilterLabel);
             for (PacketSection section : mPacketSections) {
                 // Generate code to match the packet bytes.
                 if (section.type == PacketSection.Type.MATCH) {
-                    gen.addLoadImmediate(Register.R0, section.start);
+                    gen.addLoadImmediate(R0, section.start);
                     gen.addJumpIfBytesAtR0NotEqual(
                             Arrays.copyOfRange(mPacket.array(), section.start,
                                     section.start + section.length),
@@ -1154,8 +1155,8 @@
                 } else {
                     switch (section.length) {
                         // length asserted to be either 2 or 4 on PacketSection construction
-                        case 2: gen.addLoad16(Register.R0, section.start); break;
-                        case 4: gen.addLoad32(Register.R0, section.start); break;
+                        case 2: gen.addLoad16(R0, section.start); break;
+                        case 4: gen.addLoad32(R0, section.start); break;
                     }
 
                     // WARNING: keep this in sync with matches()!
@@ -1282,21 +1283,21 @@
         void generateFilterLocked(ApfV4Generator gen) throws IllegalInstructionException {
             final String nextFilterLabel = "natt_keepalive_filter" + getUniqueNumberLocked();
 
-            gen.addLoadImmediate(Register.R0, ETH_HEADER_LEN + IPV4_SRC_ADDR_OFFSET);
+            gen.addLoadImmediate(R0, ETH_HEADER_LEN + IPV4_SRC_ADDR_OFFSET);
             gen.addJumpIfBytesAtR0NotEqual(mSrcDstAddr, nextFilterLabel);
 
             // A NAT-T keepalive packet contains 1 byte payload with the value 0xff
             // Check payload length is 1
-            gen.addLoadFromMemory(Register.R0, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
+            gen.addLoadFromMemory(R0, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
             gen.addAdd(UDP_HEADER_LEN);
             gen.addSwap();
-            gen.addLoad16(Register.R0, IPV4_TOTAL_LENGTH_OFFSET);
-            gen.addNeg(Register.R1);
+            gen.addLoad16(R0, IPV4_TOTAL_LENGTH_OFFSET);
+            gen.addNeg(R1);
             gen.addAddR1();
             gen.addJumpIfR0NotEquals(1, nextFilterLabel);
 
             // Check that the ports match
-            gen.addLoadFromMemory(Register.R0, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
+            gen.addLoadFromMemory(R0, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
             gen.addAdd(ETH_HEADER_LEN);
             gen.addJumpIfBytesAtR0NotEqual(mPortFingerprint, nextFilterLabel);
 
@@ -1398,28 +1399,28 @@
         void generateFilterLocked(ApfV4Generator gen) throws IllegalInstructionException {
             final String nextFilterLabel = "keepalive_ack" + getUniqueNumberLocked();
 
-            gen.addLoadImmediate(Register.R0, ETH_HEADER_LEN + IPV4_SRC_ADDR_OFFSET);
+            gen.addLoadImmediate(R0, ETH_HEADER_LEN + IPV4_SRC_ADDR_OFFSET);
             gen.addJumpIfBytesAtR0NotEqual(mSrcDstAddr, nextFilterLabel);
 
             // Skip to the next filter if it's not zero-sized :
             // TCP_HEADER_SIZE + IPV4_HEADER_SIZE - ipv4_total_length == 0
             // Load the IP header size into R1
-            gen.addLoadFromMemory(Register.R1, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
+            gen.addLoadFromMemory(R1, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
             // Load the TCP header size into R0 (it's indexed by R1)
-            gen.addLoad8Indexed(Register.R0, ETH_HEADER_LEN + TCP_HEADER_SIZE_OFFSET);
+            gen.addLoad8Indexed(R0, ETH_HEADER_LEN + TCP_HEADER_SIZE_OFFSET);
             // Size offset is in the top nibble, but it must be multiplied by 4, and the two
             // top bits of the low nibble are guaranteed to be zeroes. Right-shift R0 by 2.
             gen.addRightShift(2);
             // R0 += R1 -> R0 contains TCP + IP headers length
             gen.addAddR1();
             // Load IPv4 total length
-            gen.addLoad16(Register.R1, IPV4_TOTAL_LENGTH_OFFSET);
-            gen.addNeg(Register.R0);
+            gen.addLoad16(R1, IPV4_TOTAL_LENGTH_OFFSET);
+            gen.addNeg(R0);
             gen.addAddR1();
             gen.addJumpIfR0NotEquals(0, nextFilterLabel);
             // Add IPv4 header length
-            gen.addLoadFromMemory(Register.R1, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
-            gen.addLoadImmediate(Register.R0, ETH_HEADER_LEN);
+            gen.addLoadFromMemory(R1, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
+            gen.addLoadImmediate(R0, ETH_HEADER_LEN);
             gen.addAddR1();
             gen.addJumpIfBytesAtR0NotEqual(mPortSeqAckFingerprint, nextFilterLabel);
 
@@ -1521,23 +1522,23 @@
         final String checkTargetIPv4 = "checkTargetIPv4";
 
         // Drop if not ARP IPv4.
-        gen.addLoadImmediate(Register.R0, ARP_HEADER_OFFSET);
+        gen.addLoadImmediate(R0, ARP_HEADER_OFFSET);
         maybeSetupCounter(gen, Counter.DROPPED_ARP_NON_IPV4);
         gen.addJumpIfBytesAtR0NotEqual(ARP_IPV4_HEADER, mCountAndDropLabel);
 
         // Drop if unknown ARP opcode.
-        gen.addLoad16(Register.R0, ARP_OPCODE_OFFSET);
+        gen.addLoad16(R0, ARP_OPCODE_OFFSET);
         gen.addJumpIfR0Equals(ARP_OPCODE_REQUEST, checkTargetIPv4); // Skip to unicast check
         maybeSetupCounter(gen, Counter.DROPPED_ARP_UNKNOWN);
         gen.addJumpIfR0NotEquals(ARP_OPCODE_REPLY, mCountAndDropLabel);
 
         // Drop if ARP reply source IP is 0.0.0.0
-        gen.addLoad32(Register.R0, ARP_SOURCE_IP_ADDRESS_OFFSET);
+        gen.addLoad32(R0, ARP_SOURCE_IP_ADDRESS_OFFSET);
         maybeSetupCounter(gen, Counter.DROPPED_ARP_REPLY_SPA_NO_HOST);
         gen.addJumpIfR0Equals(IPV4_ANY_HOST_ADDRESS, mCountAndDropLabel);
 
         // Pass if non-broadcast reply.
-        gen.addLoadImmediate(Register.R0, ETH_DEST_ADDR_OFFSET);
+        gen.addLoadImmediate(R0, ETH_DEST_ADDR_OFFSET);
         maybeSetupCounter(gen, Counter.PASSED_ARP_UNICAST_REPLY);
         gen.addJumpIfBytesAtR0NotEqual(ETHER_BROADCAST, mCountAndPassLabel);
 
@@ -1545,13 +1546,13 @@
         gen.defineLabel(checkTargetIPv4);
         if (mIPv4Address == null) {
             // When there is no IPv4 address, drop GARP replies (b/29404209).
-            gen.addLoad32(Register.R0, ARP_TARGET_IP_ADDRESS_OFFSET);
+            gen.addLoad32(R0, ARP_TARGET_IP_ADDRESS_OFFSET);
             maybeSetupCounter(gen, Counter.DROPPED_GARP_REPLY);
             gen.addJumpIfR0Equals(IPV4_ANY_HOST_ADDRESS, mCountAndDropLabel);
         } else {
             // When there is an IPv4 address, drop unicast/broadcast requests
             // and broadcast replies with a different target IPv4 address.
-            gen.addLoadImmediate(Register.R0, ARP_TARGET_IP_ADDRESS_OFFSET);
+            gen.addLoadImmediate(R0, ARP_TARGET_IP_ADDRESS_OFFSET);
             maybeSetupCounter(gen, Counter.DROPPED_ARP_OTHER_HOST);
             gen.addJumpIfBytesAtR0NotEqual(mIPv4Address, mCountAndDropLabel);
         }
@@ -1588,17 +1589,17 @@
 
             // Pass DHCP addressed to us.
             // Check it's UDP.
-            gen.addLoad8(Register.R0, IPV4_PROTOCOL_OFFSET);
+            gen.addLoad8(R0, IPV4_PROTOCOL_OFFSET);
             gen.addJumpIfR0NotEquals(IPPROTO_UDP, skipDhcpv4Filter);
             // Check it's not a fragment or is the initial fragment.
-            gen.addLoad16(Register.R0, IPV4_FRAGMENT_OFFSET_OFFSET);
+            gen.addLoad16(R0, IPV4_FRAGMENT_OFFSET_OFFSET);
             gen.addJumpIfR0AnyBitsSet(IPV4_FRAGMENT_OFFSET_MASK, skipDhcpv4Filter);
             // Check it's addressed to DHCP client port.
-            gen.addLoadFromMemory(Register.R1, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
-            gen.addLoad16Indexed(Register.R0, TCP_UDP_DESTINATION_PORT_OFFSET);
+            gen.addLoadFromMemory(R1, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
+            gen.addLoad16Indexed(R0, TCP_UDP_DESTINATION_PORT_OFFSET);
             gen.addJumpIfR0NotEquals(DHCP_CLIENT_PORT, skipDhcpv4Filter);
             // Check it's DHCP to our MAC address.
-            gen.addLoadImmediate(Register.R0, DHCP_CLIENT_MAC_OFFSET);
+            gen.addLoadImmediate(R0, DHCP_CLIENT_MAC_OFFSET);
             // NOTE: Relies on R1 containing IPv4 header offset.
             gen.addAddR1();
             gen.addJumpIfBytesAtR0NotEqual(mHardwareAddress, skipDhcpv4Filter);
@@ -1609,14 +1610,14 @@
             gen.defineLabel(skipDhcpv4Filter);
 
             // If IPv4 destination address is in multicast range, drop.
-            gen.addLoad8(Register.R0, IPV4_DEST_ADDR_OFFSET);
+            gen.addLoad8(R0, IPV4_DEST_ADDR_OFFSET);
             gen.addAnd(0xf0);
             maybeSetupCounter(gen, Counter.DROPPED_IPV4_MULTICAST);
             gen.addJumpIfR0Equals(0xe0, mCountAndDropLabel);
 
             // If IPv4 broadcast packet, drop regardless of L2 (b/30231088).
             maybeSetupCounter(gen, Counter.DROPPED_IPV4_BROADCAST_ADDR);
-            gen.addLoad32(Register.R0, IPV4_DEST_ADDR_OFFSET);
+            gen.addLoad32(R0, IPV4_DEST_ADDR_OFFSET);
             gen.addJumpIfR0Equals(IPV4_BROADCAST_ADDRESS, mCountAndDropLabel);
             if (mIPv4Address != null && mIPv4PrefixLength < 31) {
                 maybeSetupCounter(gen, Counter.DROPPED_IPV4_BROADCAST_NET);
@@ -1639,7 +1640,7 @@
             // If L2 broadcast packet, drop.
             // TODO: can we invert this condition to fall through to the common pass case below?
             maybeSetupCounter(gen, Counter.PASSED_IPV4_UNICAST);
-            gen.addLoadImmediate(Register.R0, ETH_DEST_ADDR_OFFSET);
+            gen.addLoadImmediate(R0, ETH_DEST_ADDR_OFFSET);
             gen.addJumpIfBytesAtR0NotEqual(ETHER_BROADCAST, mCountAndPassLabel);
             maybeSetupCounter(gen, Counter.DROPPED_IPV4_L2_BROADCAST);
             gen.addJump(mCountAndDropLabel);
@@ -1660,7 +1661,7 @@
         if (!haveKeepaliveResponses) return;
 
         // If not the right proto, skip keepalive filters
-        gen.addLoad8(Register.R0, offset);
+        gen.addLoad8(R0, offset);
         gen.addJumpIfR0NotEquals(proto, label);
 
         // Drop Keepalive responses
@@ -1709,7 +1710,7 @@
         // if keepalive ack
         //   drop
 
-        gen.addLoad8(Register.R0, IPV6_NEXT_HEADER_OFFSET);
+        gen.addLoad8(R0, IPV6_NEXT_HEADER_OFFSET);
 
         // MLD packets set the router-alert hop-by-hop option.
         // TODO: be smarter about not blindly passing every packet with HBH options.
@@ -1728,7 +1729,7 @@
 
                 // ICMPv6 but not ECHO? -> Skip the multicast filter.
                 // (ICMPv6 ECHO requests will go through the multicast filter below).
-                gen.addLoad8(Register.R0, ICMP6_TYPE_OFFSET);
+                gen.addLoad8(R0, ICMP6_TYPE_OFFSET);
                 gen.addJumpIfR0NotEquals(ICMPV6_ECHO_REQUEST_TYPE, skipIPv6MulticastFilterLabel);
             } else {
                 gen.addJumpIfR0Equals(IPPROTO_ICMPV6, skipIPv6MulticastFilterLabel);
@@ -1737,7 +1738,7 @@
             // Drop all other packets sent to ff00::/8 (multicast prefix).
             gen.defineLabel(dropAllIPv6MulticastsLabel);
             maybeSetupCounter(gen, Counter.DROPPED_IPV6_NON_ICMP_MULTICAST);
-            gen.addLoad8(Register.R0, IPV6_DEST_ADDR_OFFSET);
+            gen.addLoad8(R0, IPV6_DEST_ADDR_OFFSET);
             gen.addJumpIfR0Equals(0xff, mCountAndDropLabel);
             // If any keepalive filter matches, drop
             generateV6KeepaliveFilters(gen);
@@ -1756,7 +1757,7 @@
 
         // Add unsolicited multicast neighbor announcements filter
         String skipUnsolicitedMulticastNALabel = "skipUnsolicitedMulticastNA";
-        gen.addLoad8(Register.R0, ICMP6_TYPE_OFFSET);
+        gen.addLoad8(R0, ICMP6_TYPE_OFFSET);
         // Drop all router solicitations (b/32833400)
         maybeSetupCounter(gen, Counter.DROPPED_IPV6_ROUTER_SOLICITATION);
         gen.addJumpIfR0Equals(ICMPV6_ROUTER_SOLICITATION, mCountAndDropLabel);
@@ -1766,7 +1767,7 @@
         // This is a way to cover ff02::1 and ff02::2 with a single JNEBS.
         // TODO: Drop only if they don't contain the address of on-link neighbours.
         final byte[] unsolicitedNaDropPrefix = Arrays.copyOf(IPV6_ALL_NODES_ADDRESS, 15);
-        gen.addLoadImmediate(Register.R0, IPV6_DEST_ADDR_OFFSET);
+        gen.addLoadImmediate(R0, IPV6_DEST_ADDR_OFFSET);
         gen.addJumpIfBytesAtR0NotEqual(unsolicitedNaDropPrefix, skipUnsolicitedMulticastNALabel);
 
         maybeSetupCounter(gen, Counter.DROPPED_IPV6_MULTICAST_NA);
@@ -1823,24 +1824,24 @@
         //   3. it is a UDP packet with port 5353
 
         // Check it's L2 mDNS multicast address.
-        gen.addLoadImmediate(Register.R0, ETH_DEST_ADDR_OFFSET);
+        gen.addLoadImmediate(R0, ETH_DEST_ADDR_OFFSET);
         gen.addJumpIfBytesAtR0NotEqual(ETH_MULTICAST_MDNS_V4_MAC_ADDRESS, skipMdnsv4Filter);
 
         // Checks it's IPv4.
-        gen.addLoad16(Register.R0, ETH_ETHERTYPE_OFFSET);
+        gen.addLoad16(R0, ETH_ETHERTYPE_OFFSET);
         gen.addJumpIfR0NotEquals(ETH_P_IP, skipMdnsFilter);
 
         // Check it's not a fragment.
-        gen.addLoad16(Register.R0, IPV4_FRAGMENT_OFFSET_OFFSET);
+        gen.addLoad16(R0, IPV4_FRAGMENT_OFFSET_OFFSET);
         gen.addJumpIfR0AnyBitsSet(IPV4_FRAGMENT_MORE_FRAGS_MASK | IPV4_FRAGMENT_OFFSET_MASK,
                 skipMdnsFilter);
 
         // Checks it's UDP.
-        gen.addLoad8(Register.R0, IPV4_PROTOCOL_OFFSET);
+        gen.addLoad8(R0, IPV4_PROTOCOL_OFFSET);
         gen.addJumpIfR0NotEquals(IPPROTO_UDP, skipMdnsFilter);
 
         // Set R1 to IPv4 header.
-        gen.addLoadFromMemory(Register.R1, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
+        gen.addLoadFromMemory(R1, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
         gen.addJump(checkMdnsUdpPort);
 
         gen.defineLabel(skipMdnsv4Filter);
@@ -1850,28 +1851,28 @@
         gen.addJumpIfBytesAtR0NotEqual(ETH_MULTICAST_MDNS_V6_MAC_ADDRESS, skipMdnsFilter);
 
         // Checks it's IPv6.
-        gen.addLoad16(Register.R0, ETH_ETHERTYPE_OFFSET);
+        gen.addLoad16(R0, ETH_ETHERTYPE_OFFSET);
         gen.addJumpIfR0NotEquals(ETH_P_IPV6, skipMdnsFilter);
 
         // Checks it's UDP.
-        gen.addLoad8(Register.R0, IPV6_NEXT_HEADER_OFFSET);
+        gen.addLoad8(R0, IPV6_NEXT_HEADER_OFFSET);
         gen.addJumpIfR0NotEquals(IPPROTO_UDP, skipMdnsFilter);
 
         // Set R1 to IPv6 header.
-        gen.addLoadImmediate(Register.R1, IPV6_HEADER_LEN);
+        gen.addLoadImmediate(R1, IPV6_HEADER_LEN);
 
         // Checks it's mDNS UDP port
         gen.defineLabel(checkMdnsUdpPort);
-        gen.addLoad16Indexed(Register.R0, TCP_UDP_DESTINATION_PORT_OFFSET);
+        gen.addLoad16Indexed(R0, TCP_UDP_DESTINATION_PORT_OFFSET);
         gen.addJumpIfR0NotEquals(MDNS_PORT, skipMdnsFilter);
 
-        gen.addLoad16Indexed(Register.R0, MDNS_QDCOUNT_OFFSET);
+        gen.addLoad16Indexed(R0, MDNS_QDCOUNT_OFFSET);
         // If QDCOUNT != 1, pass the packet
         gen.addJumpIfR0NotEquals(1, mDnsAcceptPacket);
 
         // If QDCOUNT == 1, matches the QNAME with allowlist.
         // Load offset for the first QNAME.
-        gen.addLoadImmediate(Register.R0, MDNS_QNAME_OFFSET);
+        gen.addLoadImmediate(R0, MDNS_QNAME_OFFSET);
         gen.addAddR1();
 
         // Check first QNAME against allowlist
@@ -1909,16 +1910,16 @@
         final String skipPort7V4Filter = "skip_port7_v4_filter";
 
         // Check it's TCP.
-        gen.addLoad8(Register.R0, IPV4_PROTOCOL_OFFSET);
+        gen.addLoad8(R0, IPV4_PROTOCOL_OFFSET);
         gen.addJumpIfR0NotEquals(IPPROTO_TCP, skipPort7V4Filter);
 
         // Check it's not a fragment or is the initial fragment.
-        gen.addLoad16(Register.R0, IPV4_FRAGMENT_OFFSET_OFFSET);
+        gen.addLoad16(R0, IPV4_FRAGMENT_OFFSET_OFFSET);
         gen.addJumpIfR0AnyBitsSet(IPV4_FRAGMENT_OFFSET_MASK, skipPort7V4Filter);
 
         // Check it's destination port 7.
-        gen.addLoadFromMemory(Register.R1, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
-        gen.addLoad16Indexed(Register.R0, TCP_UDP_DESTINATION_PORT_OFFSET);
+        gen.addLoadFromMemory(R1, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
+        gen.addLoad16Indexed(R0, TCP_UDP_DESTINATION_PORT_OFFSET);
         gen.addJumpIfR0NotEquals(ECHO_PORT, skipPort7V4Filter);
 
         // Drop it.
@@ -1964,9 +1965,9 @@
         if (mApfCapabilities.hasDataAccess()) {
             // Increment TOTAL_PACKETS
             maybeSetupCounter(gen, Counter.TOTAL_PACKETS);
-            gen.addLoadData(Register.R0, 0);  // load counter
+            gen.addLoadData(R0, 0);  // load counter
             gen.addAdd(1);
-            gen.addStoreData(Register.R0, 0);  // write-back counter
+            gen.addStoreData(R0, 0);  // write-back counter
         }
 
         // Here's a basic summary of what the initial program does:
@@ -1985,7 +1986,7 @@
         //   pass
         // insert IPv6 filter to drop, pass, or fall off the end for ICMPv6 packets
 
-        gen.addLoad16(Register.R0, ETH_ETHERTYPE_OFFSET);
+        gen.addLoad16(R0, ETH_ETHERTYPE_OFFSET);
 
         if (mDrop802_3Frames) {
             // drop 802.3 frames (ethtype < 0x0600)
@@ -2007,7 +2008,7 @@
 
         // Add mDNS filter:
         generateMdnsFilterLocked(gen);
-        gen.addLoad16(Register.R0, ETH_ETHERTYPE_OFFSET);
+        gen.addLoad16(R0, ETH_ETHERTYPE_OFFSET);
 
         // Add IPv4 filters:
         String skipIPv4FiltersLabel = "skipIPv4Filters";
@@ -2023,7 +2024,7 @@
         gen.addJumpIfR0Equals(ETH_P_IPV6, ipv6FilterLabel);
 
         // Drop non-IP non-ARP broadcasts, pass the rest
-        gen.addLoadImmediate(Register.R0, ETH_DEST_ADDR_OFFSET);
+        gen.addLoadImmediate(R0, ETH_DEST_ADDR_OFFSET);
         maybeSetupCounter(gen, Counter.PASSED_NON_IP_UNICAST);
         gen.addJumpIfBytesAtR0NotEqual(ETHER_BROADCAST, mCountAndPassLabel);
         maybeSetupCounter(gen, Counter.DROPPED_ETH_BROADCAST);
@@ -2055,16 +2056,16 @@
         // pointed to by R1, then jumps to the pass label. This saves a few bytes over inserting
         // the entire sequence inline for every counter.
         gen.defineLabel(mCountAndPassLabel);
-        gen.addLoadData(Register.R0, 0);   // R0 = *(R1 + 0)
+        gen.addLoadData(R0, 0);   // R0 = *(R1 + 0)
         gen.addAdd(1);                     // R0++
-        gen.addStoreData(Register.R0, 0);  // *(R1 + 0) = R0
+        gen.addStoreData(R0, 0);  // *(R1 + 0) = R0
         gen.addJump(gen.PASS_LABEL);
 
         // Same as above for the count & drop trampoline.
         gen.defineLabel(mCountAndDropLabel);
-        gen.addLoadData(Register.R0, 0);   // R0 = *(R1 + 0)
+        gen.addLoadData(R0, 0);   // R0 = *(R1 + 0)
         gen.addAdd(1);                     // R0++
-        gen.addStoreData(Register.R0, 0);  // *(R1 + 0) = R0
+        gen.addStoreData(R0, 0);  // *(R1 + 0) = R0
         gen.addJump(gen.DROP_LABEL);
     }
 
diff --git a/src/android/net/apf/ApfV4Generator.java b/src/android/net/apf/ApfV4Generator.java
index bc48bef..3330c36 100644
--- a/src/android/net/apf/ApfV4Generator.java
+++ b/src/android/net/apf/ApfV4Generator.java
@@ -16,6 +16,8 @@
 
 package android.net.apf;
 
+import static android.net.apf.ApfV4Generator.Rbit.Rbit0;
+import static android.net.apf.ApfV4Generator.Rbit.Rbit1;
 import static android.net.apf.ApfV4Generator.Register.R0;
 import static android.net.apf.ApfV4Generator.Register.R1;
 
@@ -161,12 +163,17 @@
         }
     }
     public enum Register {
-        R0(0),
-        R1(1);
+        R0,
+        R1;
+    }
+
+    public enum Rbit {
+        Rbit0(0),
+        Rbit1(1);
 
         final int value;
 
-        private Register(int value) {
+        Rbit(int value) {
             this.value = value;
         }
     }
@@ -296,7 +303,7 @@
 
     class Instruction {
         private final byte mOpcode;   // A "Opcode" value.
-        private final byte mRegister; // A "Register" value.
+        private final Rbit mRbit; // A "Rbit" value.
         public final List<IntImmediate> mIntImms = new ArrayList<>();
         // When mOpcode is a jump:
         private int mTargetLabelSize;
@@ -308,9 +315,18 @@
         // Offset in bytes from the beginning of this program. Set by {@link ApfGenerator#generate}.
         int offset;
 
-        Instruction(Opcodes opcode, Register register) {
+        Instruction(Opcodes opcode, Rbit rbit) {
             mOpcode = (byte) opcode.value;
-            mRegister = (byte) register.value;
+            mRbit = rbit;
+        }
+
+        Instruction(Opcodes opcode, Register register) {
+            this(opcode, register == R0 ? Rbit0 : Rbit1);
+        }
+
+        Instruction(ExtendedOpcodes extendedOpcodes, Rbit rbit) {
+            this(Opcodes.EXT, rbit);
+            addUnsigned(extendedOpcodes.value);
         }
 
         Instruction(ExtendedOpcodes extendedOpcodes, Register register) {
@@ -482,7 +498,7 @@
          */
         private byte generateInstructionByte() {
             int sizeField = generateImmSizeField();
-            return (byte)((mOpcode << 3) | (sizeField << 1) | mRegister);
+            return (byte) ((mOpcode << 3) | (sizeField << 1) | (byte) mRbit.value);
         }
 
         /**
@@ -999,8 +1015,8 @@
      * Add an instruction to the end of the program to let the program immediately return PASS.
      */
     public ApfV4Generator addPass() {
-        // PASS requires using R0 because it shares opcode with DROP
-        return append(new Instruction(Opcodes.PASSDROP));
+        // PASS requires using Rbit0 because it shares opcode with DROP
+        return append(new Instruction(Opcodes.PASSDROP, Rbit0));
     }
 
     static void checkRange(@NonNull String variableName, long value, long lowerBound,
diff --git a/src/android/net/apf/ApfV6Generator.java b/src/android/net/apf/ApfV6Generator.java
index ff6bb4d..808c697 100644
--- a/src/android/net/apf/ApfV6Generator.java
+++ b/src/android/net/apf/ApfV6Generator.java
@@ -15,8 +15,8 @@
  */
 package android.net.apf;
 
-import static android.net.apf.ApfV4Generator.Register.R0;
-import static android.net.apf.ApfV4Generator.Register.R1;
+import static android.net.apf.ApfV4Generator.Rbit.Rbit0;
+import static android.net.apf.ApfV4Generator.Rbit.Rbit1;
 
 import androidx.annotation.NonNull;
 
@@ -46,16 +46,16 @@
     public ApfV4Generator addCountAndPass(int cnt) {
         checkRange("CounterNumber", cnt /* value */, 1 /* lowerBound */,
                 1000 /* upperBound */);
-        // PASS requires using R0 because it shares opcode with DROP
-        return append(new Instruction(Opcodes.PASSDROP).addUnsigned(cnt));
+        // PASS requires using Rbit0 because it shares opcode with DROP
+        return append(new Instruction(Opcodes.PASSDROP, Rbit0).addUnsigned(cnt));
     }
 
     /**
      * Add an instruction to the end of the program to let the program immediately return DROP.
      */
     public ApfV4Generator addDrop() {
-        // DROP requires using R1 because it shares opcode with PASS
-        return append(new Instruction(Opcodes.PASSDROP, R1));
+        // DROP requires using Rbit1 because it shares opcode with PASS
+        return append(new Instruction(Opcodes.PASSDROP, Rbit1));
     }
 
     /**
@@ -65,8 +65,8 @@
     public ApfV4Generator addCountAndDrop(int cnt) {
         checkRange("CounterNumber", cnt /* value */, 1 /* lowerBound */,
                 1000 /* upperBound */);
-        // DROP requires using R1 because it shares opcode with PASS
-        return append(new Instruction(Opcodes.PASSDROP, R1).addUnsigned(cnt));
+        // DROP requires using Rbit1 because it shares opcode with PASS
+        return append(new Instruction(Opcodes.PASSDROP, Rbit1).addUnsigned(cnt));
     }
 
     /**
@@ -83,8 +83,8 @@
      * @param size the buffer length to be allocated.
      */
     public ApfV4Generator addAllocate(int size) {
-        // R1 means the extra be16 immediate is present
-        return append(new Instruction(ExtendedOpcodes.ALLOCATE, R1).addU16(size));
+        // Rbit1 means the extra be16 immediate is present
+        return append(new Instruction(ExtendedOpcodes.ALLOCATE, Rbit1).addU16(size));
     }
 
     /**
@@ -95,23 +95,24 @@
         if (!mInstructions.isEmpty()) {
             throw new IllegalInstructionException("data instruction has to come first");
         }
-        return append(new Instruction(Opcodes.JMP, R1).addUnsigned(data.length).setBytesImm(data));
+        return append(new Instruction(Opcodes.JMP, Rbit1).addUnsigned(data.length)
+                .setBytesImm(data));
     }
 
     /**
      * Add an instruction to the end of the program to transmit the allocated buffer.
      */
     public ApfV4Generator addTransmit() {
-        // TRANSMIT requires using R0 because it shares opcode with DISCARD
-        return append(new Instruction(ExtendedOpcodes.TRANSMITDISCARD));
+        // TRANSMIT requires using Rbit0 because it shares opcode with DISCARD
+        return append(new Instruction(ExtendedOpcodes.TRANSMITDISCARD, Rbit0));
     }
 
     /**
      * Add an instruction to the end of the program to discard the allocated buffer.
      */
     public ApfV4Generator addDiscard() {
-        // DISCARD requires using R1 because it shares opcode with TRANSMIT
-        return append(new Instruction(ExtendedOpcodes.TRANSMITDISCARD, R1));
+        // DISCARD requires using Rbit1 because it shares opcode with TRANSMIT
+        return append(new Instruction(ExtendedOpcodes.TRANSMITDISCARD, Rbit1));
     }
 
     /**
@@ -169,7 +170,7 @@
      * @return the ApfGenerator object
      */
     public ApfV4Generator addDataCopy(int src, int len) {
-        return append(new Instruction(Opcodes.PKTDATACOPY, R1).addUnsigned(src).addU8(len));
+        return append(new Instruction(Opcodes.PKTDATACOPY, Rbit1).addUnsigned(src).addU8(len));
     }
 
     /**
@@ -182,7 +183,7 @@
      * @return the ApfGenerator object
      */
     public ApfV4Generator addPacketCopy(int src, int len) {
-        return append(new Instruction(Opcodes.PKTDATACOPY, R0).addUnsigned(src).addU8(len));
+        return append(new Instruction(Opcodes.PKTDATACOPY, Rbit0).addUnsigned(src).addU8(len));
     }
 
     /**
@@ -194,7 +195,7 @@
      * @return the ApfGenerator object
      */
     public ApfV4Generator addDataCopyFromR0(int len) {
-        return append(new Instruction(ExtendedOpcodes.EDATACOPY).addU8(len));
+        return append(new Instruction(ExtendedOpcodes.EDATACOPY, Rbit0).addU8(len));
     }
 
     /**
@@ -206,7 +207,7 @@
      * @return the ApfGenerator object
      */
     public ApfV4Generator addPacketCopyFromR0(int len) {
-        return append(new Instruction(ExtendedOpcodes.EPKTCOPY).addU8(len));
+        return append(new Instruction(ExtendedOpcodes.EPKTCOPY, Rbit0).addU8(len));
     }
 
     /**
@@ -218,7 +219,7 @@
      * @return the ApfGenerator object
      */
     public ApfV4Generator addDataCopyFromR0LenR1() {
-        return append(new Instruction(ExtendedOpcodes.EDATACOPY, R1));
+        return append(new Instruction(ExtendedOpcodes.EDATACOPY, Rbit1));
     }
 
     /**
@@ -230,7 +231,7 @@
      * @return the ApfGenerator object
      */
     public ApfV4Generator addPacketCopyFromR0LenR1() {
-        return append(new Instruction(ExtendedOpcodes.EPKTCOPY, R1));
+        return append(new Instruction(ExtendedOpcodes.EPKTCOPY, Rbit1));
     }
 
     /**
@@ -242,7 +243,7 @@
     public ApfV4Generator addJumpIfPktAtR0DoesNotContainDnsQ(@NonNull byte[] qnames, int qtype,
                                                              @NonNull String tgt) {
         validateNames(qnames);
-        return append(new Instruction(ExtendedOpcodes.JDNSQMATCH).setTargetLabel(tgt).addU8(
+        return append(new Instruction(ExtendedOpcodes.JDNSQMATCH, Rbit0).setTargetLabel(tgt).addU8(
                 qtype).setBytesImm(qnames));
     }
 
@@ -255,7 +256,7 @@
     public ApfV4Generator addJumpIfPktAtR0ContainDnsQ(@NonNull byte[] qnames, int qtype,
                                                       @NonNull String tgt) {
         validateNames(qnames);
-        return append(new Instruction(ExtendedOpcodes.JDNSQMATCH, R1).setTargetLabel(tgt).addU8(
+        return append(new Instruction(ExtendedOpcodes.JDNSQMATCH, Rbit1).setTargetLabel(tgt).addU8(
                 qtype).setBytesImm(qnames));
     }
 
@@ -268,8 +269,8 @@
     public ApfV4Generator addJumpIfPktAtR0DoesNotContainDnsA(@NonNull byte[] names,
                                                              @NonNull String tgt) {
         validateNames(names);
-        return append(new Instruction(ExtendedOpcodes.JDNSAMATCH).setTargetLabel(tgt).setBytesImm(
-                names));
+        return append(new Instruction(ExtendedOpcodes.JDNSAMATCH, Rbit0).setTargetLabel(tgt)
+                        .setBytesImm(names));
     }
 
     /**
@@ -281,7 +282,7 @@
     public ApfV4Generator addJumpIfPktAtR0ContainDnsA(@NonNull byte[] names,
                                                       @NonNull String tgt) {
         validateNames(names);
-        return append(new Instruction(ExtendedOpcodes.JDNSAMATCH, R1).setTargetLabel(
+        return append(new Instruction(ExtendedOpcodes.JDNSAMATCH, Rbit1).setTargetLabel(
                 tgt).setBytesImm(names));
     }
 
diff --git a/src/android/net/apf/LegacyApfFilter.java b/src/android/net/apf/LegacyApfFilter.java
index d81f8b4..14ed176 100644
--- a/src/android/net/apf/LegacyApfFilter.java
+++ b/src/android/net/apf/LegacyApfFilter.java
@@ -16,6 +16,8 @@
 
 package android.net.apf;
 
+import static android.net.apf.ApfV4Generator.Register.R0;
+import static android.net.apf.ApfV4Generator.Register.R1;
 import static android.net.util.SocketUtils.makePacketSocketAddress;
 import static android.system.OsConstants.AF_PACKET;
 import static android.system.OsConstants.ARPHRD_ETHER;
@@ -44,7 +46,6 @@
 import android.net.TcpKeepalivePacketDataParcelable;
 import android.net.apf.ApfCounterTracker.Counter;
 import android.net.apf.ApfV4Generator.IllegalInstructionException;
-import android.net.apf.ApfV4Generator.Register;
 import android.net.ip.IpClient.IpClientCallbacksWrapper;
 import android.net.metrics.ApfProgramEvent;
 import android.net.metrics.ApfStats;
@@ -126,7 +127,7 @@
      */
     private void maybeSetupCounter(ApfV4Generator gen, Counter c) {
         if (mApfCapabilities.hasDataAccess()) {
-            gen.addLoadImmediate(Register.R1, c.offset());
+            gen.addLoadImmediate(R1, c.offset());
         }
     }
 
@@ -972,15 +973,15 @@
         long generateFilterLocked(ApfV4Generator gen) throws IllegalInstructionException {
             String nextFilterLabel = "Ra" + getUniqueNumberLocked();
             // Skip if packet is not the right size
-            gen.addLoadFromMemory(Register.R0, gen.PACKET_SIZE_MEMORY_SLOT);
+            gen.addLoadFromMemory(R0, gen.PACKET_SIZE_MEMORY_SLOT);
             gen.addJumpIfR0NotEquals(mPacket.capacity(), nextFilterLabel);
             // Skip filter if expired
-            gen.addLoadFromMemory(Register.R0, gen.FILTER_AGE_MEMORY_SLOT);
+            gen.addLoadFromMemory(R0, gen.FILTER_AGE_MEMORY_SLOT);
             gen.addJumpIfR0GreaterThan(filterLifetime(), nextFilterLabel);
             for (PacketSection section : mPacketSections) {
                 // Generate code to match the packet bytes.
                 if (section.type == PacketSection.Type.MATCH) {
-                    gen.addLoadImmediate(Register.R0, section.start);
+                    gen.addLoadImmediate(R0, section.start);
                     gen.addJumpIfBytesAtR0NotEqual(
                             Arrays.copyOfRange(mPacket.array(), section.start,
                                     section.start + section.length),
@@ -991,8 +992,8 @@
                 // The packet is accepted if any non-ignored lifetime is lower than filterLifetime.
                 if (isRelevantLifetime(section)) {
                     switch (section.length) {
-                        case 4: gen.addLoad32(Register.R0, section.start); break;
-                        case 2: gen.addLoad16(Register.R0, section.start); break;
+                        case 4: gen.addLoad32(R0, section.start); break;
+                        case 2: gen.addLoad16(R0, section.start); break;
                         default:
                             throw new IllegalStateException(
                                     "bogus lifetime size " + section.length);
@@ -1064,21 +1065,21 @@
         void generateFilterLocked(ApfV4Generator gen) throws IllegalInstructionException {
             final String nextFilterLabel = "natt_keepalive_filter" + getUniqueNumberLocked();
 
-            gen.addLoadImmediate(Register.R0, ETH_HEADER_LEN + IPV4_SRC_ADDR_OFFSET);
+            gen.addLoadImmediate(R0, ETH_HEADER_LEN + IPV4_SRC_ADDR_OFFSET);
             gen.addJumpIfBytesAtR0NotEqual(mSrcDstAddr, nextFilterLabel);
 
             // A NAT-T keepalive packet contains 1 byte payload with the value 0xff
             // Check payload length is 1
-            gen.addLoadFromMemory(Register.R0, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
+            gen.addLoadFromMemory(R0, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
             gen.addAdd(UDP_HEADER_LEN);
             gen.addSwap();
-            gen.addLoad16(Register.R0, IPV4_TOTAL_LENGTH_OFFSET);
-            gen.addNeg(Register.R1);
+            gen.addLoad16(R0, IPV4_TOTAL_LENGTH_OFFSET);
+            gen.addNeg(R1);
             gen.addAddR1();
             gen.addJumpIfR0NotEquals(1, nextFilterLabel);
 
             // Check that the ports match
-            gen.addLoadFromMemory(Register.R0, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
+            gen.addLoadFromMemory(R0, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
             gen.addAdd(ETH_HEADER_LEN);
             gen.addJumpIfBytesAtR0NotEqual(mPortFingerprint, nextFilterLabel);
 
@@ -1180,28 +1181,28 @@
         void generateFilterLocked(ApfV4Generator gen) throws IllegalInstructionException {
             final String nextFilterLabel = "keepalive_ack" + getUniqueNumberLocked();
 
-            gen.addLoadImmediate(Register.R0, ETH_HEADER_LEN + IPV4_SRC_ADDR_OFFSET);
+            gen.addLoadImmediate(R0, ETH_HEADER_LEN + IPV4_SRC_ADDR_OFFSET);
             gen.addJumpIfBytesAtR0NotEqual(mSrcDstAddr, nextFilterLabel);
 
             // Skip to the next filter if it's not zero-sized :
             // TCP_HEADER_SIZE + IPV4_HEADER_SIZE - ipv4_total_length == 0
             // Load the IP header size into R1
-            gen.addLoadFromMemory(Register.R1, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
+            gen.addLoadFromMemory(R1, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
             // Load the TCP header size into R0 (it's indexed by R1)
-            gen.addLoad8Indexed(Register.R0, ETH_HEADER_LEN + TCP_HEADER_SIZE_OFFSET);
+            gen.addLoad8Indexed(R0, ETH_HEADER_LEN + TCP_HEADER_SIZE_OFFSET);
             // Size offset is in the top nibble, but it must be multiplied by 4, and the two
             // top bits of the low nibble are guaranteed to be zeroes. Right-shift R0 by 2.
             gen.addRightShift(2);
             // R0 += R1 -> R0 contains TCP + IP headers length
             gen.addAddR1();
             // Load IPv4 total length
-            gen.addLoad16(Register.R1, IPV4_TOTAL_LENGTH_OFFSET);
-            gen.addNeg(Register.R0);
+            gen.addLoad16(R1, IPV4_TOTAL_LENGTH_OFFSET);
+            gen.addNeg(R0);
             gen.addAddR1();
             gen.addJumpIfR0NotEquals(0, nextFilterLabel);
             // Add IPv4 header length
-            gen.addLoadFromMemory(Register.R1, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
-            gen.addLoadImmediate(Register.R0, ETH_HEADER_LEN);
+            gen.addLoadFromMemory(R1, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
+            gen.addLoadImmediate(R0, ETH_HEADER_LEN);
             gen.addAddR1();
             gen.addJumpIfBytesAtR0NotEqual(mPortSeqAckFingerprint, nextFilterLabel);
 
@@ -1315,23 +1316,23 @@
         final String checkTargetIPv4 = "checkTargetIPv4";
 
         // Pass if not ARP IPv4.
-        gen.addLoadImmediate(Register.R0, ARP_HEADER_OFFSET);
+        gen.addLoadImmediate(R0, ARP_HEADER_OFFSET);
         maybeSetupCounter(gen, Counter.PASSED_ARP_NON_IPV4);
         gen.addJumpIfBytesAtR0NotEqual(ARP_IPV4_HEADER, mCountAndPassLabel);
 
         // Pass if unknown ARP opcode.
-        gen.addLoad16(Register.R0, ARP_OPCODE_OFFSET);
+        gen.addLoad16(R0, ARP_OPCODE_OFFSET);
         gen.addJumpIfR0Equals(ARP_OPCODE_REQUEST, checkTargetIPv4); // Skip to unicast check
         maybeSetupCounter(gen, Counter.PASSED_ARP_UNKNOWN);
         gen.addJumpIfR0NotEquals(ARP_OPCODE_REPLY, mCountAndPassLabel);
 
         // Drop if ARP reply source IP is 0.0.0.0
-        gen.addLoad32(Register.R0, ARP_SOURCE_IP_ADDRESS_OFFSET);
+        gen.addLoad32(R0, ARP_SOURCE_IP_ADDRESS_OFFSET);
         maybeSetupCounter(gen, Counter.DROPPED_ARP_REPLY_SPA_NO_HOST);
         gen.addJumpIfR0Equals(IPV4_ANY_HOST_ADDRESS, mCountAndDropLabel);
 
         // Pass if unicast reply.
-        gen.addLoadImmediate(Register.R0, ETH_DEST_ADDR_OFFSET);
+        gen.addLoadImmediate(R0, ETH_DEST_ADDR_OFFSET);
         maybeSetupCounter(gen, Counter.PASSED_ARP_UNICAST_REPLY);
         gen.addJumpIfBytesAtR0NotEqual(ETHER_BROADCAST, mCountAndPassLabel);
 
@@ -1339,13 +1340,13 @@
         gen.defineLabel(checkTargetIPv4);
         if (mIPv4Address == null) {
             // When there is no IPv4 address, drop GARP replies (b/29404209).
-            gen.addLoad32(Register.R0, ARP_TARGET_IP_ADDRESS_OFFSET);
+            gen.addLoad32(R0, ARP_TARGET_IP_ADDRESS_OFFSET);
             maybeSetupCounter(gen, Counter.DROPPED_GARP_REPLY);
             gen.addJumpIfR0Equals(IPV4_ANY_HOST_ADDRESS, mCountAndDropLabel);
         } else {
             // When there is an IPv4 address, drop unicast/broadcast requests
             // and broadcast replies with a different target IPv4 address.
-            gen.addLoadImmediate(Register.R0, ARP_TARGET_IP_ADDRESS_OFFSET);
+            gen.addLoadImmediate(R0, ARP_TARGET_IP_ADDRESS_OFFSET);
             maybeSetupCounter(gen, Counter.DROPPED_ARP_OTHER_HOST);
             gen.addJumpIfBytesAtR0NotEqual(mIPv4Address, mCountAndDropLabel);
         }
@@ -1382,17 +1383,17 @@
 
             // Pass DHCP addressed to us.
             // Check it's UDP.
-            gen.addLoad8(Register.R0, IPV4_PROTOCOL_OFFSET);
+            gen.addLoad8(R0, IPV4_PROTOCOL_OFFSET);
             gen.addJumpIfR0NotEquals(IPPROTO_UDP, skipDhcpv4Filter);
             // Check it's not a fragment. This matches the BPF filter installed by the DHCP client.
-            gen.addLoad16(Register.R0, IPV4_FRAGMENT_OFFSET_OFFSET);
+            gen.addLoad16(R0, IPV4_FRAGMENT_OFFSET_OFFSET);
             gen.addJumpIfR0AnyBitsSet(IPV4_FRAGMENT_OFFSET_MASK, skipDhcpv4Filter);
             // Check it's addressed to DHCP client port.
-            gen.addLoadFromMemory(Register.R1, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
-            gen.addLoad16Indexed(Register.R0, UDP_DESTINATION_PORT_OFFSET);
+            gen.addLoadFromMemory(R1, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
+            gen.addLoad16Indexed(R0, UDP_DESTINATION_PORT_OFFSET);
             gen.addJumpIfR0NotEquals(DHCP_CLIENT_PORT, skipDhcpv4Filter);
             // Check it's DHCP to our MAC address.
-            gen.addLoadImmediate(Register.R0, DHCP_CLIENT_MAC_OFFSET);
+            gen.addLoadImmediate(R0, DHCP_CLIENT_MAC_OFFSET);
             // NOTE: Relies on R1 containing IPv4 header offset.
             gen.addAddR1();
             gen.addJumpIfBytesAtR0NotEqual(mHardwareAddress, skipDhcpv4Filter);
@@ -1403,14 +1404,14 @@
             gen.defineLabel(skipDhcpv4Filter);
 
             // If IPv4 destination address is in multicast range, drop.
-            gen.addLoad8(Register.R0, IPV4_DEST_ADDR_OFFSET);
+            gen.addLoad8(R0, IPV4_DEST_ADDR_OFFSET);
             gen.addAnd(0xf0);
             maybeSetupCounter(gen, Counter.DROPPED_IPV4_MULTICAST);
             gen.addJumpIfR0Equals(0xe0, mCountAndDropLabel);
 
             // If IPv4 broadcast packet, drop regardless of L2 (b/30231088).
             maybeSetupCounter(gen, Counter.DROPPED_IPV4_BROADCAST_ADDR);
-            gen.addLoad32(Register.R0, IPV4_DEST_ADDR_OFFSET);
+            gen.addLoad32(R0, IPV4_DEST_ADDR_OFFSET);
             gen.addJumpIfR0Equals(IPV4_BROADCAST_ADDRESS, mCountAndDropLabel);
             if (mIPv4Address != null && mIPv4PrefixLength < 31) {
                 maybeSetupCounter(gen, Counter.DROPPED_IPV4_BROADCAST_NET);
@@ -1428,7 +1429,7 @@
             // If L2 broadcast packet, drop.
             // TODO: can we invert this condition to fall through to the common pass case below?
             maybeSetupCounter(gen, Counter.PASSED_IPV4_UNICAST);
-            gen.addLoadImmediate(Register.R0, ETH_DEST_ADDR_OFFSET);
+            gen.addLoadImmediate(R0, ETH_DEST_ADDR_OFFSET);
             gen.addJumpIfBytesAtR0NotEqual(ETHER_BROADCAST, mCountAndPassLabel);
             maybeSetupCounter(gen, Counter.DROPPED_IPV4_L2_BROADCAST);
             gen.addJump(mCountAndDropLabel);
@@ -1452,7 +1453,7 @@
         if (!haveKeepaliveResponses) return;
 
         // If not the right proto, skip keepalive filters
-        gen.addLoad8(Register.R0, offset);
+        gen.addLoad8(R0, offset);
         gen.addJumpIfR0NotEquals(proto, label);
 
         // Drop Keepalive responses
@@ -1501,7 +1502,7 @@
         // if keepalive ack
         //   drop
 
-        gen.addLoad8(Register.R0, IPV6_NEXT_HEADER_OFFSET);
+        gen.addLoad8(R0, IPV6_NEXT_HEADER_OFFSET);
 
         // MLD packets set the router-alert hop-by-hop option.
         // TODO: be smarter about not blindly passing every packet with HBH options.
@@ -1520,7 +1521,7 @@
 
                 // ICMPv6 but not ECHO? -> Skip the multicast filter.
                 // (ICMPv6 ECHO requests will go through the multicast filter below).
-                gen.addLoad8(Register.R0, ICMP6_TYPE_OFFSET);
+                gen.addLoad8(R0, ICMP6_TYPE_OFFSET);
                 gen.addJumpIfR0NotEquals(ICMPV6_ECHO_REQUEST_TYPE, skipIPv6MulticastFilterLabel);
             } else {
                 gen.addJumpIfR0Equals(IPPROTO_ICMPV6, skipIPv6MulticastFilterLabel);
@@ -1529,7 +1530,7 @@
             // Drop all other packets sent to ff00::/8 (multicast prefix).
             gen.defineLabel(dropAllIPv6MulticastsLabel);
             maybeSetupCounter(gen, Counter.DROPPED_IPV6_NON_ICMP_MULTICAST);
-            gen.addLoad8(Register.R0, IPV6_DEST_ADDR_OFFSET);
+            gen.addLoad8(R0, IPV6_DEST_ADDR_OFFSET);
             gen.addJumpIfR0Equals(0xff, mCountAndDropLabel);
             // If any keepalive filter matches, drop
             generateV6KeepaliveFilters(gen);
@@ -1548,7 +1549,7 @@
 
         // Add unsolicited multicast neighbor announcements filter
         String skipUnsolicitedMulticastNALabel = "skipUnsolicitedMulticastNA";
-        gen.addLoad8(Register.R0, ICMP6_TYPE_OFFSET);
+        gen.addLoad8(R0, ICMP6_TYPE_OFFSET);
         // Drop all router solicitations (b/32833400)
         maybeSetupCounter(gen, Counter.DROPPED_IPV6_ROUTER_SOLICITATION);
         gen.addJumpIfR0Equals(ICMPV6_ROUTER_SOLICITATION, mCountAndDropLabel);
@@ -1558,7 +1559,7 @@
         // This is a way to cover ff02::1 and ff02::2 with a single JNEBS.
         // TODO: Drop only if they don't contain the address of on-link neighbours.
         final byte[] unsolicitedNaDropPrefix = Arrays.copyOf(IPV6_ALL_NODES_ADDRESS, 15);
-        gen.addLoadImmediate(Register.R0, IPV6_DEST_ADDR_OFFSET);
+        gen.addLoadImmediate(R0, IPV6_DEST_ADDR_OFFSET);
         gen.addJumpIfBytesAtR0NotEqual(unsolicitedNaDropPrefix, skipUnsolicitedMulticastNALabel);
 
         maybeSetupCounter(gen, Counter.DROPPED_IPV6_MULTICAST_NA);
@@ -1615,19 +1616,19 @@
         //   3. it is a UDP packet with port 5353
 
         // Check it's L2 mDNS multicast address.
-        gen.addLoadImmediate(Register.R0, ETH_DEST_ADDR_OFFSET);
+        gen.addLoadImmediate(R0, ETH_DEST_ADDR_OFFSET);
         gen.addJumpIfBytesAtR0NotEqual(ETH_MULTICAST_MDNS_V4_MAC_ADDRESS,
                 skipMdnsv4Filter);
 
         // Checks it's IPv4.
-        gen.addLoad16(Register.R0, ETH_ETHERTYPE_OFFSET);
+        gen.addLoad16(R0, ETH_ETHERTYPE_OFFSET);
         gen.addJumpIfR0NotEquals(ETH_P_IP, skipMdnsFilter);
 
         // Checks it's UDP.
-        gen.addLoad8(Register.R0, IPV4_PROTOCOL_OFFSET);
+        gen.addLoad8(R0, IPV4_PROTOCOL_OFFSET);
         gen.addJumpIfR0NotEquals(IPPROTO_UDP, skipMdnsFilter);
         // Set R1 to IPv4 header.
-        gen.addLoadFromMemory(Register.R1, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
+        gen.addLoadFromMemory(R1, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
         gen.addJump(checkMdnsUdpPort);
 
         gen.defineLabel(skipMdnsv4Filter);
@@ -1637,28 +1638,28 @@
         gen.addJumpIfBytesAtR0NotEqual(ETH_MULTICAST_MDNS_V6_MAC_ADDRESS, skipMdnsFilter);
 
         // Checks it's IPv6.
-        gen.addLoad16(Register.R0, ETH_ETHERTYPE_OFFSET);
+        gen.addLoad16(R0, ETH_ETHERTYPE_OFFSET);
         gen.addJumpIfR0NotEquals(ETH_P_IPV6, skipMdnsFilter);
 
         // Checks it's UDP.
-        gen.addLoad8(Register.R0, IPV6_NEXT_HEADER_OFFSET);
+        gen.addLoad8(R0, IPV6_NEXT_HEADER_OFFSET);
         gen.addJumpIfR0NotEquals(IPPROTO_UDP, skipMdnsFilter);
 
         // Set R1 to IPv6 header.
-        gen.addLoadImmediate(Register.R1, IPV6_HEADER_LEN);
+        gen.addLoadImmediate(R1, IPV6_HEADER_LEN);
 
         // Checks it's mDNS UDP port
         gen.defineLabel(checkMdnsUdpPort);
-        gen.addLoad16Indexed(Register.R0, UDP_DESTINATION_PORT_OFFSET);
+        gen.addLoad16Indexed(R0, UDP_DESTINATION_PORT_OFFSET);
         gen.addJumpIfR0NotEquals(MDNS_PORT, skipMdnsFilter);
 
-        gen.addLoad16Indexed(Register.R0, MDNS_QDCOUNT_OFFSET);
+        gen.addLoad16Indexed(R0, MDNS_QDCOUNT_OFFSET);
         // If QDCOUNT != 1, pass the packet
         gen.addJumpIfR0NotEquals(1, mDnsAcceptPacket);
 
         // If QDCOUNT == 1, matches the QNAME with allowlist.
         // Load offset for the first QNAME.
-        gen.addLoadImmediate(Register.R0, MDNS_QNAME_OFFSET);
+        gen.addLoadImmediate(R0, MDNS_QNAME_OFFSET);
         gen.addAddR1();
 
         // Check first QNAME against allowlist
@@ -1718,9 +1719,9 @@
         if (mApfCapabilities.hasDataAccess()) {
             // Increment TOTAL_PACKETS
             maybeSetupCounter(gen, Counter.TOTAL_PACKETS);
-            gen.addLoadData(Register.R0, 0);  // load counter
+            gen.addLoadData(R0, 0);  // load counter
             gen.addAdd(1);
-            gen.addStoreData(Register.R0, 0);  // write-back counter
+            gen.addStoreData(R0, 0);  // write-back counter
         }
 
         // Here's a basic summary of what the initial program does:
@@ -1739,7 +1740,7 @@
         //   pass
         // insert IPv6 filter to drop, pass, or fall off the end for ICMPv6 packets
 
-        gen.addLoad16(Register.R0, ETH_ETHERTYPE_OFFSET);
+        gen.addLoad16(R0, ETH_ETHERTYPE_OFFSET);
 
         if (mDrop802_3Frames) {
             // drop 802.3 frames (ethtype < 0x0600)
@@ -1761,7 +1762,7 @@
 
         // Add mDNS filter:
         generateMdnsFilterLocked(gen);
-        gen.addLoad16(Register.R0, ETH_ETHERTYPE_OFFSET);
+        gen.addLoad16(R0, ETH_ETHERTYPE_OFFSET);
 
         // Add IPv4 filters:
         String skipIPv4FiltersLabel = "skipIPv4Filters";
@@ -1777,7 +1778,7 @@
         gen.addJumpIfR0Equals(ETH_P_IPV6, ipv6FilterLabel);
 
         // Drop non-IP non-ARP broadcasts, pass the rest
-        gen.addLoadImmediate(Register.R0, ETH_DEST_ADDR_OFFSET);
+        gen.addLoadImmediate(R0, ETH_DEST_ADDR_OFFSET);
         maybeSetupCounter(gen, Counter.PASSED_NON_IP_UNICAST);
         gen.addJumpIfBytesAtR0NotEqual(ETHER_BROADCAST, mCountAndPassLabel);
         maybeSetupCounter(gen, Counter.DROPPED_ETH_BROADCAST);
@@ -1809,16 +1810,16 @@
         // pointed to by R1, then jumps to the pass label. This saves a few bytes over inserting
         // the entire sequence inline for every counter.
         gen.defineLabel(mCountAndPassLabel);
-        gen.addLoadData(Register.R0, 0);   // R0 = *(R1 + 0)
+        gen.addLoadData(R0, 0);   // R0 = *(R1 + 0)
         gen.addAdd(1);                     // R0++
-        gen.addStoreData(Register.R0, 0);  // *(R1 + 0) = R0
+        gen.addStoreData(R0, 0);  // *(R1 + 0) = R0
         gen.addJump(gen.PASS_LABEL);
 
         // Same as above for the count & drop trampoline.
         gen.defineLabel(mCountAndDropLabel);
-        gen.addLoadData(Register.R0, 0);   // R0 = *(R1 + 0)
+        gen.addLoadData(R0, 0);   // R0 = *(R1 + 0)
         gen.addAdd(1);                     // R0++
-        gen.addStoreData(Register.R0, 0);  // *(R1 + 0) = R0
+        gen.addStoreData(R0, 0);  // *(R1 + 0) = R0
         gen.addJump(gen.DROP_LABEL);
     }
 
diff --git a/tests/integration/common/android/net/ip/IpClientIntegrationTestCommon.java b/tests/integration/common/android/net/ip/IpClientIntegrationTestCommon.java
index c4dc40a..72b9050 100644
--- a/tests/integration/common/android/net/ip/IpClientIntegrationTestCommon.java
+++ b/tests/integration/common/android/net/ip/IpClientIntegrationTestCommon.java
@@ -306,10 +306,10 @@
     protected static final long TEST_TIMEOUT_MS = 2_000L;
     private static final long TEST_WAIT_ENOBUFS_TIMEOUT_MS = 30_000L;
     private static final long TEST_WAIT_RENEW_REBIND_RETRANSMIT_MS = 15_000L;
-    // To prevent the flakiness about deprecationTime and expirationTime check, +/- 2s tolerance
+    // To prevent the flakiness about deprecationTime and expirationTime check, +/- 4s tolerance
     // should be enough between the timestamp when the IP provisioning completes successfully and
     // when IpClientLinkObserver sees the RTM_NEWADDR netlink events.
-    private static final long TEST_LIFETIME_TOLERANCE_MS = 2_000L;
+    private static final long TEST_LIFETIME_TOLERANCE_MS = 4_000L;
 
     @Rule
     public final DevSdkIgnoreRule mIgnoreRule = new DevSdkIgnoreRule();
diff --git a/tests/unit/src/android/net/apf/ApfTest.java b/tests/unit/src/android/net/apf/ApfTest.java
index 5c6a906..37b9060 100644
--- a/tests/unit/src/android/net/apf/ApfTest.java
+++ b/tests/unit/src/android/net/apf/ApfTest.java
@@ -263,6 +263,12 @@
         ApfV4Generator gen = new ApfV4Generator(MIN_APF_VERSION);
         assertPass(gen);
 
+        // Test pass opcode
+        gen = new ApfV4Generator(MIN_APF_VERSION);
+        gen.addPass();
+        gen.addJump(DROP_LABEL);
+        assertPass(gen);
+
         // Test jumping to pass label.
         gen = new ApfV4Generator(MIN_APF_VERSION);
         gen.addJump(PASS_LABEL);
diff --git a/tests/unit/src/android/net/apf/Bpf2Apf.java b/tests/unit/src/android/net/apf/Bpf2Apf.java
index 795c2b3..0a315e8 100644
--- a/tests/unit/src/android/net/apf/Bpf2Apf.java
+++ b/tests/unit/src/android/net/apf/Bpf2Apf.java
@@ -16,6 +16,9 @@
 
 package android.net.apf;
 
+import static android.net.apf.ApfV4Generator.Register.R0;
+import static android.net.apf.ApfV4Generator.Register.R1;
+
 import android.net.apf.ApfV4Generator.IllegalInstructionException;
 import android.net.apf.ApfV4Generator.Register;
 
@@ -67,7 +70,7 @@
             case "ldx":
             case "ldxb":
             case "ldxh":
-                Register dest = opcode.contains("x") ? Register.R1 : Register.R0;
+                Register dest = opcode.contains("x") ? R1 : R0;
                 if (arg.equals("4*([14]&0xf)")) {
                     if (!opcode.equals("ldxb")) {
                         throw new IllegalArgumentException("Unhandled instruction: " + line);
@@ -140,7 +143,7 @@
                 break;
             case "st":
             case "stx":
-                Register src = opcode.contains("x") ? Register.R1 : Register.R0;
+                Register src = opcode.contains("x") ? R1 : R0;
                 if (!arg.startsWith("M[")) {
                     throw new IllegalArgumentException("Unhandled instruction: " + line);
                 }
@@ -169,9 +172,9 @@
                             gen.addOrR1();
                             break;
                         case "sub":
-                            gen.addNeg(Register.R1);
+                            gen.addNeg(R1);
                             gen.addAddR1();
-                            gen.addNeg(Register.R1);
+                            gen.addNeg(R1);
                             break;
                     }
                 } else {
@@ -291,10 +294,10 @@
                 }
                 break;
             case "tax":
-                gen.addMove(Register.R1);
+                gen.addMove(R1);
                 break;
             case "txa":
-                gen.addMove(Register.R0);
+                gen.addMove(R0);
                 break;
             default:
                 throw new IllegalArgumentException("Unhandled instruction: " + line);
diff --git a/tests/unit/src/android/net/apf/JumpTableTest.kt b/tests/unit/src/android/net/apf/JumpTableTest.kt
index 3858aac..31b089f 100644
--- a/tests/unit/src/android/net/apf/JumpTableTest.kt
+++ b/tests/unit/src/android/net/apf/JumpTableTest.kt
@@ -16,6 +16,7 @@
 
 package android.net.apf
 
+import android.net.apf.ApfV4Generator.Register.R0
 import androidx.test.filters.SmallTest
 import androidx.test.runner.AndroidJUnit4
 import com.android.testutils.assertThrows
@@ -94,7 +95,7 @@
         j.generate(gen)
 
         inOrder.verify(gen).defineLabel(name)
-        inOrder.verify(gen).addLoadFromMemory(ApfV4Generator.Register.R0, slot)
+        inOrder.verify(gen).addLoadFromMemory(R0, slot)
         inOrder.verify(gen).addJumpIfR0Equals(0, "foo")
         inOrder.verify(gen).addJumpIfR0Equals(1, "bar")
         inOrder.verify(gen).addJumpIfR0Equals(2, "baz")
diff --git a/tests/unit/src/com/android/server/connectivity/NetworkMonitorTest.java b/tests/unit/src/com/android/server/connectivity/NetworkMonitorTest.java
index d3647f5..d6e9c8e 100644
--- a/tests/unit/src/com/android/server/connectivity/NetworkMonitorTest.java
+++ b/tests/unit/src/com/android/server/connectivity/NetworkMonitorTest.java
@@ -278,8 +278,10 @@
     private @Mock TcpSocketTracker.Dependencies mTstDependencies;
     private @Mock INetd mNetd;
     private @Mock TcpSocketTracker mTst;
-    private HashSet<WrappedNetworkMonitor> mCreatedNetworkMonitors;
-    private HashSet<BroadcastReceiver> mRegisteredReceivers;
+    @GuardedBy("mCreatedNetworkMonitors")
+    private final HashSet<WrappedNetworkMonitor> mCreatedNetworkMonitors = new HashSet<>();
+    @GuardedBy("mRegisteredReceivers")
+    private final HashSet<BroadcastReceiver> mRegisteredReceivers = new HashSet<>();
     private @Mock Context mMccContext;
     private @Mock Resources mMccResource;
     private @Mock WifiInfo mWifiInfo;
@@ -681,16 +683,22 @@
         mFakeDns.setAnswer(PRIVATE_DNS_PROBE_HOST_SUFFIX, new String[]{"2001:db8::1"}, TYPE_AAAA);
 
         doAnswer((invocation) -> {
-            mRegisteredReceivers.add(invocation.getArgument(0));
+            synchronized (mRegisteredReceivers) {
+                mRegisteredReceivers.add(invocation.getArgument(0));
+            }
             return new Intent();
         }).when(mContext).registerReceiver(any(BroadcastReceiver.class), any());
         doAnswer((invocation) -> {
-            mRegisteredReceivers.add(invocation.getArgument(0));
+            synchronized (mRegisteredReceivers) {
+                mRegisteredReceivers.add(invocation.getArgument(0));
+            }
             return new Intent();
         }).when(mContext).registerReceiver(any(BroadcastReceiver.class), any(), anyInt());
 
         doAnswer((invocation) -> {
-            mRegisteredReceivers.remove(invocation.getArgument(0));
+            synchronized (mRegisteredReceivers) {
+                mRegisteredReceivers.remove(invocation.getArgument(0));
+            }
             return null;
         }).when(mContext).unregisterReceiver(any());
 
@@ -700,12 +708,10 @@
         setDataStallEvaluationType(DATA_STALL_EVALUATION_TYPE_DNS);
         setValidDataStallDnsTimeThreshold(TEST_MIN_VALID_STALL_DNS_TIME_THRESHOLD_MS);
         setConsecutiveDnsTimeoutThreshold(5);
-        mCreatedNetworkMonitors = new HashSet<>();
-        mRegisteredReceivers = new HashSet<>();
     }
 
-    private static <T> void quitThreadsThat(Supplier<List<T>> supplier, ThrowingConsumer terminator)
-            throws Exception {
+    private static <T> void quitResourcesThat(Supplier<List<T>> supplier,
+            ThrowingConsumer terminator) throws Exception {
         // Run it multiple times since new threads might be generated in a thread
         // that is about to be terminated, e.g. each thread that runs
         // isCaptivePortal could generate 2 more probing threads.
@@ -720,8 +726,29 @@
         assertEquals(Collections.emptyList(), supplier.get());
     }
 
+    private void quitNetworkMonitors() throws Exception {
+        quitResourcesThat(() -> {
+            synchronized (mCreatedNetworkMonitors) {
+                final ArrayList<WrappedNetworkMonitor> ret =
+                        new ArrayList<>(mCreatedNetworkMonitors);
+                mCreatedNetworkMonitors.clear();
+                return ret;
+            }
+        }, (it) -> {
+            final WrappedNetworkMonitor nm = (WrappedNetworkMonitor) it;
+            nm.notifyNetworkDisconnected();
+            nm.awaitQuit();
+        });
+        synchronized (mRegisteredReceivers) {
+            assertEquals("BroadcastReceiver still registered after disconnect",
+                    0, mRegisteredReceivers.size());
+        }
+        quitThreads();
+        quitExecutorServices();
+    }
+
     private void quitExecutorServices() throws Exception {
-        quitThreadsThat(() -> {
+        quitResourcesThat(() -> {
             synchronized (mExecutorServiceToBeCleared) {
                 final ArrayList<ExecutorService> ret = new ArrayList<>(mExecutorServiceToBeCleared);
                 mExecutorServiceToBeCleared.clear();
@@ -734,7 +761,7 @@
     }
 
     private void quitThreads() throws Exception {
-        quitThreadsThat(() -> {
+        quitResourcesThat(() -> {
             synchronized (mThreadsToBeCleared) {
                 final ArrayList<Thread> ret = new ArrayList<>(mThreadsToBeCleared);
                 mThreadsToBeCleared.clear();
@@ -751,20 +778,7 @@
     @After
     public void tearDown() throws Exception {
         mFakeDns.clearAll();
-        // Make a local copy of mCreatedNetworkMonitors because during the iteration below,
-        // WrappedNetworkMonitor#onQuitting will delete elements from it on the handler threads.
-        WrappedNetworkMonitor[] networkMonitors = mCreatedNetworkMonitors.toArray(
-                new WrappedNetworkMonitor[0]);
-        for (WrappedNetworkMonitor nm : networkMonitors) {
-            nm.notifyNetworkDisconnected();
-            nm.awaitQuit();
-        }
-        assertEquals("NetworkMonitor still running after disconnect",
-                0, mCreatedNetworkMonitors.size());
-        assertEquals("BroadcastReceiver still registered after disconnect",
-                0, mRegisteredReceivers.size());
-        quitThreads();
-        quitExecutorServices();
+        quitNetworkMonitors();
         // Clear mocks to prevent from stubs holding instances and cause memory leaks.
         Mockito.framework().clearInlineMocks();
     }
@@ -849,7 +863,6 @@
         @Override
         protected void onQuitting() {
             super.onQuitting();
-            assertTrue(mCreatedNetworkMonitors.remove(this));
             mQuitCv.open();
         }
 
@@ -1171,7 +1184,9 @@
         verify(mContext, never()).registerReceiver(receiverCaptor.capture(),
                 argThat(receiver -> ACTION_CONFIGURATION_CHANGED.equals(receiver.getAction(0))));
         nm.start();
-        mCreatedNetworkMonitors.add(nm);
+        synchronized (mCreatedNetworkMonitors) {
+            mCreatedNetworkMonitors.add(nm);
+        }
         HandlerUtils.waitForIdle(nm.getHandler(), HANDLER_TIMEOUT_MS);
         verify(mContext, times(1)).registerReceiver(receiverCaptor.capture(),
                 argThat(receiver -> ACTION_CONFIGURATION_CHANGED.equals(receiver.getAction(0))));
@@ -3773,6 +3788,8 @@
         // started. If captive portal app receiver is registered, then the size of the registered
         // receivers will be 2. Otherwise, mRegisteredReceivers should only contain 1 configuration
         // change receiver.
-        assertEquals(isPortal ? 2 : 1, mRegisteredReceivers.size());
+        synchronized (mRegisteredReceivers) {
+            assertEquals(isPortal ? 2 : 1, mRegisteredReceivers.size());
+        }
     }
 }