WEBVTT 00:00.480 --> 00:01.480 Hello everyone. 00:01.520 --> 00:02.520 Typhoon here again. 00:02.840 --> 00:10.400 And today we begin one of the most fundamental and powerful journeys into low level programming understanding 00:10.880 --> 00:20.520 x86 64 assembly or understanding the registers in x86 64 assembly. 00:20.520 --> 00:26.840 So if you want to know how CPU thinks, how it manipulates data, executes instructions, and controls 00:26.840 --> 00:32.360 memory, then you must understand the registers. 00:34.200 --> 00:41.120 Now, this lecture is long, dense, and packed with everything from beginner insights into detailed 00:41.160 --> 00:47.560 breakdowns meant for feature reverse engineers and low level programmers. 00:48.080 --> 00:52.360 So you may ask here, what are the registers? 00:54.120 --> 01:02.400 At the lowest level of computing, a register is tiny, lightning fast piece of memory inside the CPU 01:02.440 --> 01:03.080 itself. 01:03.730 --> 01:10.650 registers temporarily store data that's being actively used or manipulated by the CPU. 01:11.370 --> 01:15.930 They are fundamental to every operation your processor performs. 01:17.930 --> 01:22.690 Now you can think of the registers as the working hands of the CPU. 01:22.850 --> 01:30.810 So instead of grabbing data from random access memory or Ram every time, which is much slower compared 01:30.810 --> 01:39.650 to the CPU, the CPU first grabs it into a register, manipulates it under, and then sends the results 01:39.650 --> 01:43.170 back to the random access memory Ram if needed. 01:43.730 --> 01:50.930 In x86 assembly, there are multiple types of registers, each grounded based on function or grouped 01:50.970 --> 01:52.010 based on function. 01:52.370 --> 01:56.010 The first we have g a. 01:57.010 --> 01:58.690 This is not a universal GPA here. 01:58.690 --> 02:01.410 This is general purpose registers. 02:01.970 --> 02:04.650 This perform like arithmetics. 02:06.410 --> 02:10.570 Logic and memory access. 02:12.370 --> 02:20.450 And we also have the segment registers which manage segmented memory addressing. 02:24.490 --> 02:33.170 We have the flags register which tracks the results and CPU states after operations. 02:34.930 --> 02:47.530 And we also have the instruction pointers like I, p e p and r I p. 02:49.930 --> 02:52.850 Which basically shows where the current instruction is. 02:54.730 --> 03:00.090 Now let's let's dissect each category right now. 03:01.810 --> 03:05.970 First we will start with the general purpose registers. 03:09.820 --> 03:11.460 General purpose registers. 03:11.820 --> 03:20.060 So the original x86 architecture began with 36 bit general purpose registers. 03:20.460 --> 03:21.420 These include. 03:21.420 --> 03:26.180 The first is accumulator a x. 03:27.180 --> 03:28.740 Let's actually change the color. 03:28.740 --> 03:30.260 Write it in a different color. 03:32.420 --> 03:33.100 A x. 03:33.500 --> 03:38.460 So this is accumulator used heavily for arithmetic multiplication and system calls. 03:39.300 --> 03:42.460 We have base register b. 03:44.860 --> 03:47.860 Often stores base addresses in memory operations. 03:48.020 --> 03:58.300 We have C control register commonly used in loop operations such as uh rep mov esp. 03:59.940 --> 04:04.620 Let's actually also write the abbreviation for this uh, as well. 04:05.180 --> 04:15.220 Uh, we have the X uh, which is data register, often used alongside a uh in division multiple action. 04:15.220 --> 04:25.900 Also for input output port addresses we have the source index um and uh destination index. 04:27.860 --> 04:36.620 Uh now uh, these used in string operations and array traversal, we have stack pointer uh points to 04:36.620 --> 04:37.740 the top of the stack. 04:37.740 --> 04:46.380 And we have the base pointer, uh, helps access functions, parameters and local variables within the 04:46.380 --> 04:46.860 stack. 04:49.740 --> 04:55.900 Let's also write the abbreviation so you can see it as we explained. 04:57.580 --> 04:58.660 Now here we are. 04:59.140 --> 05:05.420 Uh now this register can also be split into eight bit halves. 05:06.140 --> 05:18.390 Now for example in the A we have the A h, which is the high byte, and a L, which is the low byte. 05:18.990 --> 05:33.270 And for example, in B, we have the b h, which is the high byte low byte, not byte. 05:33.350 --> 05:34.950 Sorry, it was a bit. 05:34.950 --> 05:35.790 So remember. 05:36.070 --> 05:39.310 So eight bits 16 bits. 05:40.710 --> 05:45.030 And yeah same applies for the other registers as well. 05:45.070 --> 06:04.310 Say x to C 16 bit c eight bit d, l for eight, d H for 16 bit again and d L for. 06:06.750 --> 06:07.470 Eight bits. 06:07.670 --> 06:09.870 Since L here means low. 06:14.040 --> 06:17.440 And same goes on like this as well. 06:18.800 --> 06:25.560 Now that means you can manipulate single bytes efficiently, which is extremely useful for low level 06:25.560 --> 06:26.440 data handling. 06:26.720 --> 06:38.320 And when x86 architecture was extended into uh, 32 bit uh, also called the I. 06:40.680 --> 06:57.720 32 now these registers became the uh EAX, which is uh e a uh like e b x for the base register. 07:00.240 --> 07:04.480 E c for the counter register. 07:04.960 --> 07:05.280 E. 07:07.720 --> 07:16.520 For the data register, like s I E. 07:17.080 --> 07:17.520 S. 07:19.360 --> 07:19.760 I. 07:20.000 --> 07:21.240 And so on and so forth. 07:22.480 --> 07:30.000 And, uh, in the 64 bit, uh, which is what we call it the. 07:32.120 --> 07:37.880 In the 64 bit which written is like that x 86. 07:37.880 --> 07:40.000 Let's actually use a different color so we don't. 07:41.720 --> 07:42.120 Yeah. 07:42.520 --> 07:47.000 For example x 86. 07:48.800 --> 07:51.560 Now this is 64 bit. 07:53.120 --> 07:57.480 So remember this was the 16 bit 32 bit uh here. 07:57.880 --> 08:02.200 And the 64 bit registers we have here. 08:02.240 --> 08:07.680 Now the most used uh today is 64 bit registers, but depends on the CPU architecture as well. 08:08.720 --> 08:13.120 Um now they expand it to the Rax. 08:15.200 --> 08:22.850 Uh accumulator rb X for the base register. 08:23.210 --> 08:23.690 RC. 08:25.930 --> 08:27.970 For the contour register. 08:28.810 --> 08:38.650 R D for the data register and added from R eight. 08:39.530 --> 08:45.570 From R eight all the way to the R 15. 08:47.770 --> 09:03.610 Making 16 full general purpose register number 1234567 and from R81234567 and from the R eight to R 09:03.650 --> 09:10.090 15, it just um, 16 uh full general purpose register. 09:10.290 --> 09:13.170 And we all have the stack pointers as well. 09:13.490 --> 09:22.290 Now uh SP and uh BP also transition to and also get another meanings. 09:22.610 --> 09:25.810 Uh, so uh SP. 09:27.890 --> 09:31.010 SP turns to ESP here. 09:32.810 --> 09:40.650 P and uh E for the base pointer. 09:45.050 --> 09:50.090 Uh, now this points to the top of the stack. 09:50.450 --> 09:53.130 Changes automatically with the push and pop instructions. 09:53.450 --> 09:55.850 And for the, uh, 64 bits. 09:55.930 --> 09:59.050 Uh, it also changed in the 64 bit. 09:59.050 --> 10:04.850 We have the r s p and r p p here. 10:06.410 --> 10:10.610 Uh, here, SP stack pointer turns to 32 bit ESP. 10:10.610 --> 10:14.610 And in the 64 bit we use the r s p. 10:16.530 --> 10:20.610 So uh, RSP is pointing to the top of the stack. 10:20.850 --> 10:25.940 Changes automatically with the push and pop instructions and beep. 10:26.620 --> 10:27.380 Beep beep. 10:27.420 --> 10:30.100 These are basically the base pointer as well. 10:30.260 --> 10:34.020 Base pointer to reference the stack frame, which is this. 10:34.460 --> 10:36.580 We will use this in a function calls. 10:37.460 --> 10:46.340 Now every register can be accessed in parts like rax x x like like this rax. 10:46.340 --> 10:56.780 We can use the rax to the e to the x here. 10:57.340 --> 11:04.700 And for the lowest we have the a, l and a h, which I have explained here. 11:06.060 --> 11:16.460 Number and the bits increase and increase as from left from right to left in this diagram uh, which 11:16.500 --> 11:19.220 allows for flexible manipulation of data sites. 11:19.220 --> 11:27.300 So if you, if you don't need the 64 bit registers, um, but you're competing on the 64 bit CPU. 11:27.700 --> 11:28.900 You can just use a. 11:29.460 --> 11:31.380 So from this to save the. 11:31.540 --> 11:38.580 From computing power, which you will learn that more deeply in next lectures. 11:39.900 --> 11:44.820 Uh, now let's also explain the instruction, uh, pointers. 11:46.220 --> 11:51.740 In the next lecture, uh, this was the part one of the first lecture. 11:51.780 --> 11:57.020 Uh, this is, as I said, from the starting of this, uh, lecture. 11:57.300 --> 12:03.060 Uh, these are very important, uh, for learning assembler languages. 12:03.060 --> 12:07.060 It doesn't matter if it's an an R or another assembler language. 12:07.180 --> 12:14.220 If you know the base understanding of this, how assembler works, uh, you can apply the same principles 12:14.220 --> 12:23.460 on R or other Masm or other assembly languages here. 12:23.860 --> 12:24.980 So thank you for watching. 12:25.020 --> 12:27.740 I'm Tiffany and I'm waiting you in next lecture.