[GDB] Handle kill and detach packets.

This commit also includes a test to ensure that single stepping works,
since continue, kill, detach, and single step all share code.

src/core/gdbstub.c

 		case 'M':
 			gdbstub_write_mem ( stub );
 			break;
-		case 'c':
-			gdbstub_continue ( stub, 0 );
-			break;
-		case 's':
-			gdbstub_continue ( stub, 1 );
+		case 'c': /* Continue */
+		case 'k': /* Kill */
+		case 's': /* Step */
+		case 'D': /* Detach */
+			gdbstub_continue ( stub, stub->payload [ 0 ] == 's' );
+			if ( stub->payload [ 0 ] == 'D' ) {
+				gdbstub_send_ok ( stub );
+			}
 			break;
 		default:
 			stub->len = 0;

src/tests/gdbstub_test.S

 	int	$3
 	addl	$8, %esp
 
+	/* 5. Step test */
+	int	$3
+	nop
+
 1:
 	jmp	1b

src/tests/gdbstub_test.gdb

 	gpxe_assert ({char}($esp)) (char)0x99 "gpxe_test_mem_write char"
 end
 
+define gpxe_test_step
+	c
+	si
+	gpxe_assert ({char}($eip-1)) (char)0x90 "gpxe_test_step" # nop = 0x90
+end
+
 gpxe_load_symbols
 gpxe_connect
 gpxe_start_tests
 gpxe_test_regs_write
 gpxe_test_mem_read
 gpxe_test_mem_write
+gpxe_test_step