WEBVTT 00:00.610 --> 00:01.450 Hello, my name is Steve. 00:01.630 --> 00:02.560 Welcome to this lecture. 00:02.560 --> 00:06.940 And in this lecture we are going to compile this program, create a mac file for it. 00:06.940 --> 00:10.850 And also I will explain this code line by line first. 00:10.900 --> 00:15.310 First of all, let's actually make our code look nicer here. 00:15.310 --> 00:18.970 Let's add a enter here, the new line. 00:19.960 --> 00:22.120 Have a new line. 00:22.120 --> 00:22.960 And also. 00:24.290 --> 00:25.280 New line here. 00:25.280 --> 00:28.880 So the code is going to be read for us. 00:29.810 --> 00:30.710 And that's it. 00:30.890 --> 00:36.620 So now here, let's get started by explaining this code by line by line. 00:36.860 --> 00:44.390 And what we're going to do is firstly, I will explain this data section, which are which we are defining 00:44.420 --> 00:47.560 the various data variables with different sizes. 00:47.570 --> 00:50.600 So actually we also need the grommet. 00:50.720 --> 00:53.510 Let's actually mark it down to. 00:57.660 --> 01:00.540 Now we are I'm explaining this data here. 01:00.540 --> 01:07.770 So in the first year in Vietnam, we are defining a bite size. 01:07.770 --> 01:12.390 In this case, eight bits for this exploit. 01:13.920 --> 01:17.100 Okay, So this is eight bits. 01:17.940 --> 01:21.750 Um, variable with the value of one, two, three. 01:21.750 --> 01:23.490 And in w num. 01:23.490 --> 01:30.960 Here we are defining a word size in this case, 16 bits. 01:32.010 --> 01:37.100 Um, 16 bits variable with the value of one, two, three, four, five. 01:37.110 --> 01:42.450 And in the Num we are defining a double word size. 01:42.450 --> 01:52.530 In this case it is 32 bits, a variable with a value of 1234567890. 01:52.530 --> 02:02.280 And in num one we are defining a quad word size variable with the value of this here. 02:02.280 --> 02:10.170 In this case, this variable size is 64 bits here, 64 bits. 02:10.590 --> 02:15.360 In this case it's 32 bits, 16 bits and eight bits. 02:15.570 --> 02:21.570 And also in num one, yes, we are defining the 64 bits we already explained. 02:21.570 --> 02:31.660 And in M2 we are defining another quad word size variable with the value of one, two, three, four, 02:31.660 --> 02:32.440 five, six. 02:32.440 --> 02:43.180 In this case, this is also 64 bit and also this is also 64 bit because we defined that as a quad word 02:43.180 --> 02:44.590 size variable. 02:44.590 --> 02:52.480 So and in N3 we are again defining a codeword size variable with the value of 3.14. 02:52.690 --> 02:56.020 It is also 64 bits here. 02:57.280 --> 03:05.350 And here in the section, the section will normally contain initialized data, uninitialized data. 03:05.350 --> 03:09.000 But it seems like there's a we didn't add. 03:09.250 --> 03:18.400 No variables are defined in the section because we don't have any unusual uninitialized data here and 03:18.490 --> 03:20.380 here in this section. 03:20.380 --> 03:29.440 We as you can see, yes, in the section text here, this is the section is for code instruction. 03:29.440 --> 03:37.660 This global main directive specifies that the symbol main is globally accessible entry point for the 03:37.660 --> 03:38.500 program. 03:38.500 --> 03:45.880 And also we have this main push rb r, BP and RWP rsp. 03:46.240 --> 03:51.130 This is this main label marks the start of the main function. 03:51.490 --> 03:58.250 So this code sets up a basic function prologue by saving saving the current value of the base pointer 03:58.280 --> 04:07.640 r bp onto the stack and then copying the current stack pointer rsp into our BP here. 04:08.210 --> 04:13.720 So and after that, we have four lines of code defined here. 04:13.730 --> 04:22.780 So this is for the these are the instructions, um, manip to manipulate the rax register. 04:22.790 --> 04:26.870 This is a general purpose 64 bit register. 04:26.870 --> 04:29.750 So rax is 64 bit. 04:29.750 --> 04:37.640 But you can also open this cheat sheet cheat sheet for the 64 bit registers here. 04:37.640 --> 04:40.880 So 64 bit registers. 04:40.880 --> 04:51.170 So here, as I added comments here, the move rax minus one fills the entire rax register with ones. 04:51.530 --> 04:58.100 This move a l bite b num loads the value of b num. 04:58.110 --> 05:05.540 In this case b is 123 into the lower eight bits of rax preserving the upper bits. 05:05.540 --> 05:09.680 And also we have the XOR rax rax. 05:09.680 --> 05:17.590 This clears all bits, all bits in rax and move a l bite b num. 05:17.600 --> 05:23.660 Again, we are using one, two, three calls, we are using B now which holds the value of 123. 05:23.690 --> 05:32.270 This loads the value of b num into the lower eight bits of rax now correctly here, so similar instructions 05:32.270 --> 05:35.300 are used for this. 05:39.020 --> 05:39.520 Here. 05:39.560 --> 05:51.920 A similar instructions are used for here, a x and a word here, a keyword and a x, which is, as you 05:51.920 --> 05:53.410 can see, for Vina. 05:54.650 --> 06:01.520 And so we are again manipulating this rax register here. 06:01.700 --> 06:07.960 So move rax minus one again fills the rax with once more rax keyword w num. 06:09.170 --> 06:13.090 Loads the value of uh, the PR uh. 06:14.260 --> 06:16.000 W I'm here again. 06:16.000 --> 06:22.090 But this is the almost the same with this one here in the previous one. 06:22.090 --> 06:25.240 But what's interesting here is this. 06:25.420 --> 06:28.920 So again, we are at the start. 06:28.930 --> 06:30.520 We are all the same. 06:30.520 --> 06:39.820 So we are moving the racks, move racks minus one is fills the entire racks register with once again. 06:39.820 --> 06:42.760 You can also use this to learn this registers. 06:42.760 --> 06:46.300 You can also open the Nasm cheat sheet. 06:47.410 --> 06:50.680 You can find that in anywhere. 06:50.890 --> 06:54.940 So you can use that to learn about these registers as well. 06:54.940 --> 07:01.000 So here after that we move racks Keyboard Keenan one. 07:01.120 --> 07:04.930 This loads the value of Keenan into racks. 07:05.260 --> 07:14.510 So we are in this here we are overwriting the previous value of racks and move keyword to Num2 racks. 07:14.510 --> 07:19.850 This stores the value of racks into enum to. 07:20.870 --> 07:24.680 And the lastly mov rax 123456. 07:24.710 --> 07:29.840 This loads the immediate value of 123456 in Rax. 07:29.840 --> 07:40.580 And lastly, what we have here actually we need to instead of using that we need to use mov s mov. 07:45.400 --> 07:46.390 Move here. 07:46.420 --> 07:47.080 So. 07:48.420 --> 07:48.930 Move. 07:51.300 --> 07:52.230 Or still here? 07:52.230 --> 07:52.800 Yes. 07:52.920 --> 07:53.280 This. 07:53.280 --> 07:56.280 This here needs to move here. 07:56.280 --> 07:56.910 So move. 07:56.940 --> 08:05.910 SD So this instruction loads double precision floating point number from the memory location key M3 08:05.910 --> 08:08.580 into Xmm0 register. 08:08.580 --> 08:15.240 And also keep in mind that must is a special instructions for handling floating point number because 08:15.240 --> 08:26.820 in Q and M3 we have the floating point number which is 3.14, and after that we just have several instructions. 08:27.210 --> 08:34.410 So this is here, these instructions here mov rsp rbp pop rbp here. 08:34.410 --> 08:40.470 So these instructions perform the function Epilogue Storing the stack pointer, rsp and base pointer 08:40.510 --> 08:43.410 are to their original values. 08:43.440 --> 08:47.220 This ret instructions is new to us here. 08:47.220 --> 08:49.410 This RET instruction is new to us. 08:49.440 --> 08:54.760 This instruction returns from the main function which we didn't actually use that. 08:55.730 --> 08:55.990 Lecture. 08:56.090 --> 08:58.730 So please also keep in mind that this code is. 08:59.610 --> 09:03.870 The x86 64 assembly language and syntax. 09:03.870 --> 09:11.580 While I explained individual lines, it's important to make sure that code is properly assembled and 09:11.580 --> 09:14.740 executed with a within a suitable environment. 09:14.760 --> 09:22.200 And now what we're going to do is we will first compile it with the make. 09:22.350 --> 09:29.160 We will create the make file in the next lecture and we will also use the triple dee dee dee dee debugger 09:29.160 --> 09:37.320 for debugging our application, which obviously this this will not provide any console output like printing 09:37.320 --> 09:46.680 the words Hello world, but it actually does operations in memory which we will uh, analyze that and 09:46.680 --> 09:48.270 debug that in next lecture. 09:48.270 --> 09:49.620 So I'm waiting you in next lecture.