WEBVTT 1 00:00.440 --> 00:02.180 Hello and welcome back. 2 00:02.180 --> 00:07.820 In this lesson, we are going to learn how to swap data between two memory addresses. 3 00:08.630 --> 00:14.360 We thought that maybe you could do something like this, but this is an illegal instruction. 4 00:14.360 --> 00:19.040 It is not permitted to exchange directly two memory addresses. 5 00:19.040 --> 00:20.900 So how do we solve this? 6 00:22.520 --> 00:23.090 The tip: 7 00:23.840 --> 00:25.370 Use the register. 8 00:26.630 --> 00:35.090 So just pause the video and give this a try on your own, and then come back later and watch the solution 9 00:35.090 --> 00:35.870 below. 10 00:37.810 --> 00:38.890 So good luck. 11 00:43.030 --> 00:43.600 Okay. 12 00:43.600 --> 00:45.190 I hope that you gave it a try. 13 00:45.370 --> 00:47.620 Let's scroll down to see the solution. 14 00:47.980 --> 00:50.830 So the solution is to move memory, 15 00:51.040 --> 00:54.670 the first memory to the - register. 16 00:55.690 --> 01:00.610 This is a temporary register to hold the data in memory one. 17 01:01.210 --> 01:04.480 Then we swap the memory two with the register. 18 01:05.440 --> 01:09.190 And finally, we move whatever is in the register to memory one. 19 01:09.940 --> 01:12.550 So let's try this now in the x64dbg. 20 01:13.510 --> 01:17.440 I've opened up my template two and let's 21 01:17.860 --> 01:21.370 now put a breakpoint and run to the breakpoint. 22 01:21.880 --> 01:22.840 Step over. 23 01:23.830 --> 01:25.720 So now we come to this line. 24 01:26.080 --> 01:29.620 We are going to put data in memory one and two. 25 01:30.040 --> 01:36.520 So let's go to memory map and select the data segment and select two addresses. 26 01:37.360 --> 01:38.230 First address. 27 01:38.230 --> 01:39.910 Maybe we can use this one. 28 01:40.270 --> 01:45.910 So we copy this out, copy address and put it here. 29 01:50.890 --> 01:51.730 Then, 30 01:51.730 --> 01:54.280 now let's choose another address. 31 01:57.300 --> 01:59.130 Maybe the one after that. 32 01:59.910 --> 02:00.570 The next one. 33 02:00.570 --> 02:03.570 Let's copy this address and put it here as well. 34 02:05.910 --> 02:07.530 Let's go back to the first one. 35 02:08.070 --> 02:09.330 The first one is here. 36 02:09.330 --> 02:12.600 So we select this address and put some value there. 37 02:13.440 --> 02:18.240 So binary edit. We'll put 1111. 38 02:18.900 --> 02:19.680 Okay. 39 02:21.540 --> 02:28.500 Now we go to the second address and right-click and we binary edit. 40 02:29.550 --> 02:31.830 And we put 2222. 41 02:33.210 --> 02:38.670 So now the challenge is to swap data between these two addresses. 42 02:38.670 --> 02:41.010 That means 1111. 43 02:41.040 --> 02:44.520 You want to swap it to over here. 44 02:45.030 --> 02:48.810 Here should become 1111 and 2222. 45 02:48.840 --> 02:50.160 We will swap it up. 46 02:50.370 --> 02:52.500 So 2222 will move up here. 47 02:52.530 --> 02:57.930 So at the end of this, you should have 2222 on top and 1111 below. 48 02:58.560 --> 02:59.850 So let's do that now. 49 03:00.720 --> 03:03.690 First step is to move memory one to -. 50 03:03.810 --> 03:05.370 So this is memory one. 51 03:06.750 --> 03:10.020 Memory one is containing the value 1111. 52 03:10.290 --> 03:13.590 What if we try to do this directly? 53 03:15.220 --> 03:17.320 XCHG two memory directly. 54 03:18.430 --> 03:20.140 Let's try that and see what happens. 55 03:25.030 --> 03:25.570 We put 56 03:27.140 --> 03:31.280 memory one and now memory two. 57 03:36.390 --> 03:38.490 And you will see the error here. 58 03:39.780 --> 03:41.370 Instruction encoding error. 59 03:41.370 --> 03:42.360 Invalid instruction. 60 03:42.600 --> 03:45.780 So this proves that you cannot swap memory directly. 61 03:45.780 --> 03:52.380 You have to use the register to act as a temporary holding area. 62 03:52.950 --> 03:55.920 So the first step is to move memory one to -. 63 03:56.100 --> 03:57.630 So this one doesn't work. 64 03:57.630 --> 04:00.900 So let's cancel this and do it the correct way. 65 04:01.560 --> 04:07.260 So the correct way first is to move your memory to -. 66 04:07.680 --> 04:09.330 So let's do that now. 67 04:14.200 --> 04:15.310 Memory one. 68 04:21.680 --> 04:25.790 Copy memory one and paste it here. 69 04:31.850 --> 04:33.380 Now we step over this. 70 04:35.320 --> 04:36.280 In memory one, 71 04:36.280 --> 04:40.000 whatever is in memory one is now copied to -. 72 04:40.480 --> 04:43.210 Next one is exchange with memory two. 73 04:43.210 --> 04:47.080 That means whatever is here, you want to swap it with memory two. 74 04:47.890 --> 04:48.700 So let's do that. 75 04:48.700 --> 04:50.350 Now we copy memory two. 76 05:04.990 --> 05:06.130 Paste memory two. 77 05:08.470 --> 05:08.710 Hit 78 05:08.710 --> 05:09.340 okay. 79 05:10.570 --> 05:13.780 Now we step over this and we should see this. 80 05:14.200 --> 05:17.470 - 1111 will be swapped with memory two. 81 05:20.340 --> 05:22.350 You know it has been swapped. 82 05:22.980 --> 05:25.590 1111 is now in the memory. 83 05:25.620 --> 05:26.700 Memory two. 84 05:26.700 --> 05:30.720 And whatever was in memory two has been swapped into -. 85 05:31.320 --> 05:36.120 So the final step is to move this value in - to memory one. 86 05:38.670 --> 05:40.680 So we assemble. 87 05:40.680 --> 05:41.490 Move. 88 05:48.120 --> 05:48.660 We copy 89 05:48.660 --> 05:49.410 memory one. 90 05:52.830 --> 05:54.150 And we paste here. 91 06:00.730 --> 06:01.300 Okay. 92 06:02.560 --> 06:04.120 And now we step over this. 93 06:05.120 --> 06:10.760 And we see now memory one now has got the value two two two two. 94 06:11.450 --> 06:16.190 So this is how you can swap values in two memories. 95 06:16.430 --> 06:20.930 You need to use a temporary register as a holding area. 96 06:21.410 --> 06:23.150 So that's all for this video. 97 06:23.150 --> 06:24.380 Thank you for watching.