WEBVTT 1 00:02.410 --> 00:03.910 Hello and welcome back. 2 00:03.910 --> 00:09.100 In this video, we are going to do another if-else statement. 3 00:09.220 --> 00:10.600 Earlier on, we did if statement. 4 00:10.600 --> 00:12.670 So this time we are going to do if-else. 5 00:13.390 --> 00:15.340 So if-else statement, 6 00:15.370 --> 00:16.270 it looks like this. 7 00:16.270 --> 00:23.380 Assuming we have two variables A and B, and we will perform an if statement to compare the values in 8 00:23.380 --> 00:24.280 A and B. 9 00:24.280 --> 00:30.700 So if A is larger than B, then we assign three to B, else we assign three to A, then we end if. 10 00:30.700 --> 00:34.870 So to implement this in assembly, we will do something like this. 11 00:34.870 --> 00:36.520 So there is an address here. 12 00:36.520 --> 00:47.080 The label is if. Move QWORD PTR, the value in A to -, and then compare with the B, and if it's greater, 13 00:47.080 --> 00:49.120 then we jump greater. 14 00:49.120 --> 00:52.690 So we jump to the else label, which is also another address. 15 00:52.690 --> 00:59.050 However, if - is not larger than B, then we will not jump. 16 00:59.050 --> 01:03.850 Instead, we will continue to step through and perform this assignment. 17 01:03.850 --> 01:11.800 We will move three to A, and then when we finish doing that, we will jump to another address. 18 01:11.800 --> 01:15.820 And if we don't jump here, it will step through and perform the else part. 19 01:15.820 --> 01:18.250 That's why it is important to jump here. 20 01:18.760 --> 01:21.340 So all these are actually just addresses. 21 01:21.340 --> 01:25.330 So we have to find the addresses for A, B, else, and endif. 22 01:26.230 --> 01:26.590 Right. 23 01:26.590 --> 01:32.020 So the first thing we do is open your template2.exe. 24 01:32.020 --> 01:35.650 And then we will look for addresses for all of these. 25 01:35.890 --> 01:42.520 So A, B will be addresses in your BSS segment because they are variables. Else 26 01:42.520 --> 01:46.960 and endif will be the addresses in your instruction section, 27 01:46.960 --> 01:49.960 here, your text section, which is your instruction section. 28 01:50.380 --> 01:57.310 So for A and B, let's select dump one first and then go to memory map and look at BSS. 29 01:57.310 --> 01:59.350 Right-click on it and follow in dump. 30 01:59.950 --> 02:04.570 And here we will select two addresses, one for A and one for B. 31 02:04.570 --> 02:09.610 So let's scroll down somewhere at the bottom here and let us select this for A. 32 02:09.640 --> 02:15.640 So right-click this address, copy address, and then we paste it in here. 33 02:15.940 --> 02:18.490 So this is your first address. 34 02:18.760 --> 02:21.370 And then now we go to another location. 35 02:21.370 --> 02:23.170 Select this one for B. 36 02:23.830 --> 02:26.800 We copy the address and we paste it in here. 37 02:28.840 --> 02:30.130 So that is done. 38 02:30.850 --> 02:31.240 Else 39 02:31.240 --> 02:36.790 and endif, we will look somewhere down here at the bottom. We scroll down somewhere to the bottom. 40 02:36.790 --> 02:44.110 And maybe here we would do else over here, or maybe high up here, else. 41 02:44.110 --> 02:49.390 So we just right-click this address, copy this address, and we put it here. 42 02:50.860 --> 02:52.960 And endif will be the end of the if statement. 43 02:52.960 --> 02:55.300 So we can safely put it somewhere down here. 44 02:55.300 --> 03:00.250 So right-click this, copy the address, and put it down here. 45 03:01.090 --> 03:02.830 So we have four addresses. 46 03:03.220 --> 03:07.750 So let's go to the top here now and code all this. 47 03:07.930 --> 03:11.890 So the first one is to move this - QWORD PTR A. 48 03:11.890 --> 03:14.230 So we copy this address A first. 49 03:16.510 --> 03:21.970 Copy this, and then we go to this location and assemble our move. 50 03:28.910 --> 03:29.960 So that is done. 51 03:29.960 --> 03:31.760 We paste our address that we copied. 52 03:32.270 --> 03:35.000 Next one would be compare this with B. 53 03:35.000 --> 03:37.130 So let's copy B's address. 54 03:41.320 --> 03:43.660 So we come back here, we compare. 55 03:52.280 --> 03:58.160 Paste the address for B, hit okay, then we will jump to else if greater. 56 03:58.160 --> 04:00.740 So over here we copy the else address. 57 04:03.850 --> 04:08.290 Come back here and we paste our address there. 58 04:08.290 --> 04:13.720 Be sure to put the 0x in front of all addresses, the prefix, and then 59 04:13.720 --> 04:14.440 okay. 60 04:14.590 --> 04:18.760 And then we do this, move this to address A. 61 04:18.760 --> 04:20.290 So you copy address A again. 62 04:38.330 --> 04:41.600 And then we jump to endif, endif address over here. 63 04:41.600 --> 04:42.980 Let's copy the address. 64 04:52.720 --> 04:54.610 And then finally the else part. 65 04:54.610 --> 04:59.410 So we go to the else part over here and do this instruction. 66 04:59.410 --> 05:00.790 So we go to the else part. 67 05:01.000 --> 05:04.180 So the else part is somewhere down here, 68 05:04.180 --> 05:06.730 0x401586. 69 05:06.730 --> 05:12.910 So we go down to 0x401586 over here. 70 05:12.910 --> 05:13.960 586. 71 05:14.050 --> 05:16.990 So over here we will do this instruction. 72 05:17.860 --> 05:20.410 We will copy this, three to B. 73 05:20.410 --> 05:21.610 So address B is here. 74 05:21.610 --> 05:23.170 So we copy the address first. 75 05:27.170 --> 05:30.080 Come back to this one and then we move. 76 05:34.920 --> 05:35.910 Move three there. 77 05:36.750 --> 05:36.900 Here. 78 05:36.900 --> 05:37.440 Okay. 79 05:39.450 --> 05:40.980 All right, so it's done. 80 05:40.980 --> 05:45.750 So now just do a check to see we got it correct. 81 05:46.050 --> 05:48.330 So the first one is move 82 05:48.360 --> 05:50.730 -, 0x407100. 83 05:51.330 --> 05:55.020 Move -, 0x407100. 84 05:55.110 --> 05:57.000 Next one is compare with 85 05:57.000 --> 06:02.820 0x407120, 0x407120. 86 06:03.360 --> 06:06.480 Next one is jump 0x401586. 87 06:07.260 --> 06:11.460 Jump to else, which is 0x401586. 88 06:11.460 --> 06:11.850 Correct. 89 06:12.180 --> 06:16.650 Next is move 0x407103. 90 06:17.220 --> 06:21.450 Move 0x407103, and last. 91 06:21.450 --> 06:24.150 Next one is jump to 0x4015B9. 92 06:24.390 --> 06:27.930 Jump to 0x4015B9. 93 06:28.170 --> 06:34.170 And then the last one will be this statement at the else address. 94 06:34.170 --> 06:36.480 So else address is over here, 95 06:37.080 --> 06:44.220 0x401586, where we move B to three. 96 06:44.220 --> 06:49.530 So B is 0x407120, 0x407120, 3. 97 06:49.530 --> 06:49.890 Correct. 98 06:49.890 --> 06:51.660 So we are ready to execute this now. 99 06:51.870 --> 06:56.970 So we run. Before that, we have to put some values in the variables. 100 06:56.970 --> 07:02.610 So for A, we are going to put one. For B, we are going to put two. 101 07:02.700 --> 07:12.750 So we go to variable A, 0x407100, 0x407100. 102 07:13.170 --> 07:16.140 Right-click here and binary edit. 103 07:16.140 --> 07:18.030 And we put one over there. 104 07:19.080 --> 07:21.600 Be sure to put 01 and not 10, okay? 105 07:21.660 --> 07:23.760 Because it's little-endian convention. 106 07:23.760 --> 07:26.370 So when you read this back, it reads in reverse order. 107 07:26.370 --> 07:32.520 It will be 00, 00, 00, 00, 00, all the way to the end, 01. 108 07:32.520 --> 07:34.800 So this means one, not ten. 109 07:34.800 --> 07:34.950 Yeah. 110 07:34.950 --> 07:36.960 You don't put 10 here, 01. 111 07:36.960 --> 07:42.210 So this is variable A. Variable A is now having the value one. 112 07:42.210 --> 07:45.960 Next, we are going to initialize variable B with two. 113 07:45.990 --> 07:50.160 So variable B is this address, 0x407120, over here. 114 07:50.340 --> 07:52.770 So we are going to assign two there. 115 07:52.770 --> 07:55.560 So right-click here, binary edit. 116 07:55.560 --> 07:59.340 And here we put 02, okay. 117 07:59.730 --> 08:03.120 So now we got one in A and two in B. 118 08:03.120 --> 08:04.500 So we are ready to run. 119 08:04.500 --> 08:06.090 So we run to our breakpoint. 120 08:06.090 --> 08:11.940 Step over. It's going to move variable A to -. 121 08:12.300 --> 08:13.860 Step over. - 122 08:14.040 --> 08:17.460 now is one because it just moved one from variable A to -. 123 08:17.760 --> 08:20.880 Next, it's going to compare - with variable two. 124 08:20.880 --> 08:24.240 Variable B, sorry. Variable B is this one with two. 125 08:24.270 --> 08:25.650 So it's going to compare that. 126 08:26.040 --> 08:29.460 So after compare, it's going to test whether variable A is bigger. 127 08:29.460 --> 08:31.380 If variable A is bigger, then it will jump. 128 08:31.380 --> 08:32.670 But in this case, it is not. 129 08:32.670 --> 08:33.870 So it doesn't jump. 130 08:33.870 --> 08:37.590 That's why the grayed-out arrow is shown instead of red. 131 08:38.220 --> 08:39.510 So now it's not going to jump. 132 08:39.510 --> 08:41.250 It's going to move forward straight away. 133 08:41.640 --> 08:42.750 It's going to move forward. 134 08:43.140 --> 08:45.450 And it's going to move three to variable A. 135 08:45.480 --> 08:47.070 So variable A is this. 136 08:47.070 --> 08:48.000 So it's going to move three. 137 08:48.000 --> 08:51.060 Then step over, and you find three is being moved there. 138 08:51.780 --> 08:55.560 Then finally, it's going to jump all the way out into the endif part. 139 08:55.560 --> 09:00.930 So step over. You see that the red arrow here, red arrow is highlighted, meaning it's going to jump 140 09:00.930 --> 09:01.140 here. 141 09:01.140 --> 09:02.040 So step over. 142 09:02.250 --> 09:04.050 And true enough, it jumps over here. 143 09:04.530 --> 09:09.930 So this is how we can implement if-else statements inside your assembly. 144 09:09.930 --> 09:11.400 You need to do some planning. 145 09:11.400 --> 09:16.710 You have to set up all the addresses for the variables and the instructions before you can implement 146 09:16.710 --> 09:16.950 it. 147 09:17.100 --> 09:18.690 So that's all for this video. 148 09:18.690 --> 09:19.860 Thank you for watching.