Index: head/sys/gdb/gdb.h
===================================================================
--- head/sys/gdb/gdb.h
+++ head/sys/gdb/gdb.h
@@ -55,6 +55,9 @@
 					   deadcode and never invoked for so
 					   long I don't want to just blindly
 					   start invoking it without opt-in. */
+#define	GDB_DBGP_FEAT_RELIABLE	0x2	/* The debugport promises it is a
+					   reliable transport, which allows GDB
+					   acks to be turned off. */
 
 #define	GDB_DBGPORT(name, probe, init, term, getc, putc)		\
 	static struct gdb_dbgport name##_gdb_dbgport = {		\
Index: head/sys/gdb/gdb_int.h
===================================================================
--- head/sys/gdb/gdb_int.h
+++ head/sys/gdb/gdb_int.h
@@ -54,6 +54,8 @@
 extern size_t gdb_rxsz;
 extern char *gdb_txp;
 
+extern bool gdb_ackmode;
+
 #ifdef DDB
 /* If set, return to DDB when controlling GDB detaches. */
 extern bool gdb_return_to_ddb;
@@ -132,6 +134,20 @@
 gdb_tx_varhex(uintmax_t n)
 {
 	gdb_txp += sprintf(gdb_txp, "%jx", n);
+}
+
+static __inline void
+gdb_nack(void)
+{
+	if (gdb_ackmode)
+		gdb_cur->gdb_putc('-');
+}
+
+static __inline void
+gdb_ack(void)
+{
+	if (gdb_ackmode)
+		gdb_cur->gdb_putc('+');
 }
 
 #endif /* !_GDB_GDB_INT_H_ */
Index: head/sys/gdb/gdb_main.c
===================================================================
--- head/sys/gdb/gdb_main.c
+++ head/sys/gdb/gdb_main.c
@@ -57,6 +57,7 @@
 
 struct gdb_dbgport *gdb_cur = NULL;
 int gdb_listening = 0;
+bool gdb_ackmode = true;
 
 static unsigned char gdb_bindata[64];
 
@@ -262,6 +263,14 @@
 	gdb_tx_str(";qXfer:threads:read+");
 
 	/*
+	 * If the debugport is a reliable transport, request No Ack mode from
+	 * the server.  The server may or may not choose to enter No Ack mode.
+	 * https://sourceware.org/gdb/onlinedocs/gdb/Packet-Acknowledgment.html
+	 */
+	if (gdb_cur->gdb_dbfeatures & GDB_DBGP_FEAT_RELIABLE)
+		gdb_tx_str(";QStartNoAckMode+");
+
+	/*
 	 * Future consideration:
 	 *   - vCont
 	 *   - multiprocess
@@ -610,6 +619,8 @@
 	}
 
 	gdb_listening = 0;
+	gdb_ackmode = true;
+
 	/*
 	 * Send a T packet. We currently do not support watchpoints (the
 	 * awatch, rwatch or watch elements).
@@ -759,6 +770,22 @@
 			} else if (gdb_rx_equal("Search:memory:")) {
 				gdb_do_mem_search();
 			} else if (!gdb_cpu_query())
+				gdb_tx_empty();
+			break;
+		case 'Q':
+			if (gdb_rx_equal("StartNoAckMode")) {
+				if ((gdb_cur->gdb_dbfeatures &
+				    GDB_DBGP_FEAT_RELIABLE) == 0) {
+					/*
+					 * Shouldn't happen if we didn't
+					 * advertise support.  Reject.
+					 */
+					gdb_tx_empty();
+					break;
+				}
+				gdb_ackmode = false;
+				gdb_tx_ok();
+			} else
 				gdb_tx_empty();
 			break;
 		case 's': {	/* Step. */
Index: head/sys/gdb/gdb_packet.c
===================================================================
--- head/sys/gdb/gdb_packet.c
+++ head/sys/gdb/gdb_packet.c
@@ -134,18 +134,28 @@
 
 		/* Bail out on a buffer overflow. */
 		if (c != '#') {
-			gdb_cur->gdb_putc('-');
+			gdb_nack();
 			return (ENOSPC);
 		}
 
+		/*
+		 * In Not-AckMode, we can assume reliable transport and neither
+		 * need to verify checksums nor send Ack/Nack.
+		 */
+		if (!gdb_ackmode)
+			break;
+
 		c = gdb_getc();
 		cksum -= (C2N(c) << 4) & 0xf0;
 		c = gdb_getc();
 		cksum -= C2N(c) & 0x0f;
-		gdb_cur->gdb_putc((cksum == 0) ? '+' : '-');
-		if (cksum != 0)
+		if (cksum == 0) {
+			gdb_ack();
+		} else {
+			gdb_nack();
 			printf("GDB: packet `%s' has invalid checksum\n",
 			    gdb_rxbuf);
+		}
 	} while (cksum != 0);
 
 	gdb_rxp = gdb_rxbuf;
@@ -336,6 +346,14 @@
 		gdb_cur->gdb_putc(N2C(c));
 
 getack:
+		/*
+		 * In NoAckMode, it is assumed that the underlying transport is
+		 * reliable and thus neither conservant sends acknowledgements;
+		 * there is nothing to wait for here.
+		 */
+		if (!gdb_ackmode)
+			break;
+
 		c = gdb_getc();
 	} while (c != '+');
 
Index: head/sys/gdb/netgdb.c
===================================================================
--- head/sys/gdb/netgdb.c
+++ head/sys/gdb/netgdb.c
@@ -272,7 +272,7 @@
 	.gdb_putc = netgdb_dbg_putc,
 	.gdb_term = netgdb_fini,
 	.gdb_sendpacket = netgdb_dbg_sendpacket,
-	.gdb_dbfeatures = GDB_DBGP_FEAT_WANTTERM,
+	.gdb_dbfeatures = GDB_DBGP_FEAT_WANTTERM | GDB_DBGP_FEAT_RELIABLE,
 };
 
 static void