WEBVTT 00:00.290 --> 00:04.910 Welcome to this exciting tutorial on x86 64 assembly programming. 00:04.940 --> 00:11.690 In this lecture we will walk you through the process of creating a classic Hello World application using 00:11.720 --> 00:20.630 Nasm Assembly and GCC on a Linux system and assembly language might seem intimidating, but don't worry, 00:20.630 --> 00:25.360 we will break it down step by step, making it easy to understand. 00:25.370 --> 00:30.120 And before we dive into the code, let's talk about the tools we will be using. 00:30.140 --> 00:38.930 Nasm Short for Netwide Assembler is a powerful assembler for the x86 architecture and it allows us to 00:38.930 --> 00:45.740 write low level code using human readable mnemonics which will be translated into machine code. 00:45.770 --> 00:53.870 On the other hand, GCC and compiler collection will help us link our assembly code into an executable 00:53.870 --> 00:54.590 program. 00:54.590 --> 01:03.000 In this case, we will use the CSM, which is an IDE for assembler, but you can also use the regular 01:03.000 --> 01:04.920 text editor for this project. 01:04.920 --> 01:10.710 And here we will open this project here, right click on it, or actually we can also create a new file 01:10.710 --> 01:11.610 with this. 01:11.850 --> 01:17.790 And see here we are on the assembly directory, which we will create our project in this directory here. 01:17.790 --> 01:19.500 So we will use the. 01:20.660 --> 01:22.010 Make file. 01:22.580 --> 01:22.940 Oops. 01:23.060 --> 01:23.470 Sorry. 01:23.480 --> 01:25.220 Clear Pouch. 01:26.690 --> 01:27.620 Um, here. 01:27.740 --> 01:29.750 And after that, we will create our. 01:31.340 --> 01:33.160 And as you can see here, we will. 01:33.170 --> 01:35.480 We created our hello ASM here. 01:35.510 --> 01:39.370 Now we will go to open project and click on Hello ASM. 01:39.380 --> 01:42.800 And as you can see here, our file is empty for now. 01:42.800 --> 01:47.510 But we will fill this and write our codes in this file right now. 01:47.510 --> 01:51.680 So firstly, we will need the section for data here. 01:52.870 --> 01:54.100 Data section here. 01:54.910 --> 01:55.570 Data. 01:55.570 --> 01:57.000 And after that we will. 01:57.010 --> 01:57.550 Hello. 01:57.550 --> 01:59.560 And I will explain all of these codes. 01:59.590 --> 02:04.360 Now, after writing this code, Hello world. 02:06.810 --> 02:13.440 And we will also add zero, which you will learn why we added right at this zero right here. 02:13.590 --> 02:18.510 This is a null terminated terminated string. 02:18.750 --> 02:23.010 And after that we will also create a text section. 02:23.440 --> 02:26.580 So section text. 02:27.090 --> 02:29.730 And here we will global. 02:30.650 --> 02:31.150 Part. 02:31.760 --> 02:35.270 And we will now write our start here. 02:38.800 --> 02:43.900 And here we will write the add our commands. 02:48.050 --> 02:49.090 Hello, world. 02:49.520 --> 02:52.580 To start out. 02:53.190 --> 02:58.710 Which this is in the file descriptor one. 02:59.670 --> 03:00.450 The Scripture. 03:00.480 --> 03:01.380 The Scripture. 03:01.500 --> 03:04.830 And after that we will move. 03:05.760 --> 03:06.910 Use the tab. 03:06.930 --> 03:09.090 MOV rax one. 03:10.580 --> 03:13.970 Okay to use spaces between this comma and your. 03:15.310 --> 03:18.730 Here because it makes it easier to read. 03:18.730 --> 03:22.930 And before comment, you can add two tabs. 03:24.520 --> 03:25.030 Call. 03:26.050 --> 03:27.660 I'll number. 03:28.880 --> 03:30.950 Number for Seasprite. 03:31.710 --> 03:35.250 And or the I also one. 03:37.950 --> 03:41.760 And this is for the file descriptor. 03:45.990 --> 03:48.570 One, which is STD out. 03:51.900 --> 03:54.810 Here and we will also remove the error. 03:56.850 --> 03:57.090 You. 03:57.210 --> 03:57.720 Hello. 03:57.720 --> 04:03.930 And here, as you can see here, we created our hello data in the data section so we can use this variable. 04:05.140 --> 04:08.980 And we will point the we will pointer to the string. 04:09.010 --> 04:11.110 To the string to. 04:11.120 --> 04:12.040 Right. 04:12.220 --> 04:13.930 And after that. 04:15.070 --> 04:16.840 Move are the. 04:18.350 --> 04:20.660 Richard Burton here. 04:20.750 --> 04:25.730 This is the verdict, this 13 here, because this is the length of the string. 04:26.000 --> 04:28.640 Now we will add the length. 04:34.120 --> 04:35.710 Let's count this again. 04:35.800 --> 04:40.720 One, two, three, four, five, six, seven, eight, nine, ten. 04:41.710 --> 04:43.920 11, 12, 13. 04:43.930 --> 04:52.360 And here, if you want to count the string, you need to start from one and not zero like in an array. 04:52.360 --> 04:52.790 Right? 04:52.810 --> 04:56.560 You will need to start counting from one. 04:56.560 --> 05:03.790 So the first alphabet is one count as one, and after that we will go to. 05:05.730 --> 05:10.020 Uh, Siskel, We will invoke the system. 05:10.020 --> 05:11.040 Call here. 05:11.580 --> 05:14.790 Invoke the system call. 05:14.790 --> 05:17.880 And after that, we will need to exit the program. 05:18.000 --> 05:21.840 So exit the program. 05:21.900 --> 05:25.540 So move rax 60. 05:25.830 --> 05:27.180 This is for the. 05:28.240 --> 05:31.600 This is for the Siskel number forces exit. 05:33.270 --> 05:41.260 I'll number four's exit and X or D, A or D. 05:41.880 --> 05:48.510 So this is for the returning code zero return code zero. 05:48.510 --> 05:51.450 And lastly, we will also create the syscall. 05:52.450 --> 05:54.700 This skull, which is this for? 05:54.700 --> 05:58.480 Again, invoke the system call. 06:00.010 --> 06:00.790 And here. 06:00.790 --> 06:01.510 That's it. 06:01.540 --> 06:03.820 Now, let's explain this code. 06:04.180 --> 06:04.960 And. 06:06.070 --> 06:12.610 This code starts by defining two sections data and text. 06:13.420 --> 06:19.960 Uh, so this data section, this section is used to declare the data segments of the program. 06:20.080 --> 06:28.320 Here we define a variable named hello and assign the string Hello world to it. 06:28.330 --> 06:36.400 So the DB directive is used to define data bytes and we terminate the string with a null character to 06:36.400 --> 06:37.010 embark. 06:37.030 --> 06:38.650 This is the end of the string. 06:38.650 --> 06:41.290 And we also have the text section here. 06:41.290 --> 06:44.390 This section contains the actual code of the program. 06:44.410 --> 06:51.430 We mark the entry point of our program using the Global Start Declaration, and the Start label serves 06:51.430 --> 06:54.520 as the entry point of our application. 06:54.520 --> 06:57.940 And in this start here, as you can see here. 06:59.100 --> 07:02.640 Um, we in the this this is the text section. 07:03.090 --> 07:12.660 The start we proceed to write the code to print hello world to the screen and exit to exit from the 07:12.660 --> 07:13.770 program here. 07:14.890 --> 07:16.160 And the. 07:16.360 --> 07:19.180 So here we will see. 07:19.180 --> 07:21.850 Here we will we added some comments here. 07:21.850 --> 07:28.930 But now let's start with our first line in the start in the stack section. 07:29.730 --> 07:34.740 So this line loads the syscall number for this, right? 07:34.770 --> 07:35.670 This is the system. 07:36.560 --> 07:40.550 System call to overwrite data into the Rax register. 07:40.550 --> 07:45.950 So this number one represents the size right here. 07:45.980 --> 07:46.610 Right. 07:46.610 --> 07:59.750 So move the i comma one so we load the file descriptor for standard output STD out into the d register. 07:59.750 --> 08:08.390 So file descriptor one corresponds to stdout which is the screen and MOV rsi. 08:08.420 --> 08:08.960 Hello. 08:08.990 --> 08:18.050 The RSI register is loaded with the memory address of the hello variable which points to our hello world 08:18.050 --> 08:18.860 string. 08:18.860 --> 08:19.550 Right. 08:19.550 --> 08:23.870 And after that we have mov rdx 13. 08:23.870 --> 08:30.680 So we select the RDX register to the length of the string which is the 13 characters, including this 08:30.680 --> 08:33.380 new Terminator and the syscall. 08:33.380 --> 08:41.070 This instruction invokes the system call with the values loaded into the registers, effectively printing 08:41.100 --> 08:48.180 hello world to the string and the next we add code to exit the program gracefully. 08:48.180 --> 08:50.850 So here we have mov rax 60. 08:51.030 --> 08:56.490 As I explained this, this line loads the syscall number for this exit. 08:56.580 --> 09:05.790 This is the system call to terminate the program into rax register and we have xor r the i r d i this. 09:05.820 --> 09:14.250 We set the d register to zero, indicating the return code of zero in this case success for the program. 09:14.250 --> 09:16.410 And lastly, we have the syscall. 09:16.440 --> 09:22.650 The fiscal interaction invokes the system exit system call with a return code. 09:22.680 --> 09:30.720 So this concise hello world program in x86 64 assembly and the code uses Linux system calls to print 09:30.720 --> 09:33.060 the strings and exit the program. 09:33.060 --> 09:39.780 And now let's proceed with the detailed explanation of the code and the process of assembling and executing 09:39.780 --> 09:41.430 it using Nasm. 09:42.200 --> 09:42.890 And. 09:44.330 --> 09:49.250 So here now, we will need to compile this code here. 09:50.800 --> 09:53.980 And in order to do that, we will open our terminal again. 09:53.980 --> 09:55.630 Let's clear the terminal. 09:55.630 --> 10:03.610 So we are in the disassembly directory where our our Hello dot ASM file resides. 10:03.610 --> 10:07.690 So we will pat the Hello dot ASM. 10:07.840 --> 10:10.180 As you can see here, this is our assembler program. 10:10.360 --> 10:12.430 Now we will compile it. 10:12.430 --> 10:15.520 So we will open the terminal and navigate to the directory. 10:15.520 --> 10:18.310 As you can see here, we are already navigated. 10:18.340 --> 10:20.500 Then you will use this. 10:20.530 --> 10:26.230 Nasm f elf 64 elf 64. 10:26.230 --> 10:27.630 Hello dot ASM. 10:28.880 --> 10:30.110 Output file here. 10:30.110 --> 10:31.250 Hello, All here. 10:31.250 --> 10:33.530 And as you can see here, we have this. 10:33.530 --> 10:36.230 Hello, newly created Hello all file here. 10:36.230 --> 10:40.100 And after that we will also create the GCC to linking. 10:40.130 --> 10:44.480 We will use the GCC for linking purposes. 10:44.630 --> 10:48.850 So no start files and all here. 10:48.860 --> 10:49.640 Hello. 10:50.430 --> 10:51.600 Hello, Dot all. 10:51.900 --> 10:56.970 And as you can see, we got some warning, but, uh, the program will work here. 10:57.150 --> 10:58.110 This is for the. 11:00.210 --> 11:01.080 Mining purposes. 11:01.080 --> 11:03.980 And as you can see, we have created our hello here. 11:03.990 --> 11:05.880 Now we will execute this. 11:06.030 --> 11:14.910 And as you can see here, our hello world is Hello World Assembly program that we've wrote in this lecture 11:14.910 --> 11:16.050 is works. 11:17.180 --> 11:17.630 Here. 11:17.630 --> 11:26.990 And with this method here we compile this directly assembles hello dot code using nasm and then links 11:26.990 --> 11:32.000 it into an executable using GCC without using the makefile. 11:32.000 --> 11:39.110 And if this still produces any errors, please ensure that you are using the system with nasm and GCC 11:39.860 --> 11:41.240 properly installed. 11:41.240 --> 11:43.670 And I'm waiting you in next lecture.