X86 registers

Any additional parameters get pushed on the stack. Similar to high level languages, ARM supports operations on different datatypes. [1] Registers usually consist of a small amount of fast storage, although some Register growth in the x86 CPU family has come about by extending registers existing in older CPUs. Intel® Advanced Performance Extensions (Intel® APX) expands the entire x86 instruction set with access to more registers and adds various new features that improve general-purpose performance. Using FS and GS segments in user space applications ¶. i r a: print all register, include floating point & vector register (xmm, ymm, zmm). 6 Code Segment Registers. Extended Feature Enable Register (EFER) is a model-specific register added in the AMD K6 processor, to allow enabling the SYSCALL/SYSRET instruction, and later for entering and exiting long mode. Processor register. Contains the physical address of the highest-level page table. the 80286 and later processors, also have three descriptor registers (GDTR, LDTR, IDTR) and a task register (TR). These registers are used for inputs and outputs for different CPU instruction. There are 16 64-bit registers in the x86 architecture. is_reg Checks if the given string parameter is a valid x86 register (any size). May 20, 2010 · The number of registers on a modern x86 CPU is well beyond what the CPU reveals - the CPU maintains shadow registers which are renamed as needed based upon the instruction flow. The CPU has a small number of registers, and they are tiny in size, less than 64 bits. But reading and storing data from memory slows down the processor. The PUSHA (push all) and PUSHAD (push all double) mnemonics reference the same opcode. Bit 14 indicates (when set) that the debug exception was triggered by the single-step execution mode (enabled with TF bit in EFLAGS). sub rsp,32+8; parameter area, and stack alignment. So the list of general-purpose registers is like this: Learn about the different sizes and types of registers in x86 assembly language, and how to convert values between them. A processor register is a quickly accessible location available to a computer's processor. Having the capability to manage floating point numbers means a few things: General-purpose registers (64-bit naming conventions) [+/-] 틀:Main 64-bit x86 adds 8 more general-purpose registers, named R8, R9, R10 and so on up to R15. So they implemented the idea of "Segments" - a 64 kilobyte block of memory indexed by the 16-bit address registers - that could be re-based to address different areas of the total memory. ( Only writing a 32-bit register implicitly zero-extends to 64) Besides, xorw requires an operand-size prefix to encode, so it's the same size as xorq, larger than xorl. Modern (i. Therefore the processor has storage of it’s own called registers. For example, MXCSR is used with vector instructions, and would therefore be listed with the other vector registers. Counter: The rep and loop instructions are using this register for counting. Any configuration registers are listed with the group that they are associated with. 2 Status Registers. The __fastcall convention uses registers for the first four arguments, and the stack frame to pass more Jun 10, 2021 · GDT and IDT: Base address 32 or 64 bits (in protected and long mode respectively) Limit: 16 bits. To make that work, the notion of processor registers is virtualized as well. The extensions are designed to provide efficient performance Oct 24, 2016 · 10. Oct 25, 2023 · Register Syntax. The basic kinds of assembly instructions are: Computation. Oct 29, 2020 · In the previous part of this article, I have described the basic methods of getting and setting the baseline registers of 32-bit and 64-bit x86 CPUs. 16 SSE Registers. If the interrupt handler code is simply a stub that forwards to C code, you don't need to save all of the registers. I have covered General Purpose Registers, baseline Floating-Point Registers and Debug Registers along with their ptrace(2) interface. This table gives all the basic registers, with special-purpose registers highlighted in yellow. x86 processors are limited to a 32-bit address space, allowing them to access up to 4 GB of RAM. The size and meanings of the flag bits are architecture dependent. The debugger can control registers and floating-point registers. The Intel x86 processor uses complex instruction set computer (CISC) architecture, which means there is a modest number of special-purpose registers instead of large quantities of general-purpose registers. mov eax, [esp+4] ; Move the vaule of register the memory at address (esp + 4) and store into eax. Also note how different MOV opcodes are available for 16- and 32-bit registers and values (r16, r32). The extensions for these data types are: -h or -sh for halfwords, -b or -sb Jan 15, 2019 · 6. The processor increments %rip automatically after each instruction, and control flow instructions like branches set the value of %rip to change the next instruction. The register width also determines the amount of memory a computer can utilize. Thus, x64 allows the CPU to store more data and access it faster. In Protected mode you use a logical address in the form A:B to address memory. Registers are faster than disk memory and main memory (RAM). They are 64 bit wide and they are actually aliases for the mantissa parts of the x87 registers (but they are not affected by the FPU top of the stack position); this was done to keep compatibility with existing operating systems (which already saved the FPU stack on Jul 20, 2022 · The processor stores frequently used data in a register for quick access. 16 General Purpose Registers. icted in Figure 1. Describes the format of the instruction and provides reference pages for instructions. A CS107 joint staff effort (Erik, Julie, Nate) x86-64 (also known as just x64 and/or AMD64) is the 64-bit version of the x86/IA32 instruction set. The general-purpose registers (or GPRs) are the primary registers in the x86-64 register model. If you are using MASM expression syntax, you can omit the at sign for certain very May 30, 2021 · A new ISA being designed for the high-performance use-cases where x86 competes would very likely have 32 integer registers. g. x86 （エックスはちろく [1] ）は、 Intel 8086 およびその 命令セットアーキテクチャ 、およびそれと 互換性 を備えた 命令セット を持つ マイクロプロセッサ 群の総称である。. for instance Windows x64 uses the GS register to access the TLS (thread local storage) and in Linux it's for accessing cpu specific memory. The FLAGS register is the status register that contains the current state of an x86 CPU. e 386 and beyond) x86 processors have 8 32-bit general purpose registers, as depicted in Figure 1. As their name implies, they are the only registers that are general purpose: each has a set of conventional uses 1, but programmers are generally free to ignore those conventions and use them as they please 2. Mar 5, 2024 · Today, we are introducing the next major step in the evolution of Intel® architecture. e 386 and beyond) x86 processors have eight 32-bit general purpose registers, as depicted in Figure 1. We usually use these names in our Mar 20, 2020 · So R in RAX stood for register, and was a way to unify the naming to be more consistent with the new R8 – R15 registers. 8 FPU/MMX Registers. The register names for the first eight registers are mostly historical in nature; the last eight registers were give. is_reg8_att FLAGS register. According to Intel, in x64, the following registers are called general-purpose registers (RAX, RBX, RCX, RDX, RBP, RSI, RDI, RSP and R8-R15). For the question, RBX is not R2. The segment base address is added to the Byte-address to May 16, 2024 · Examples of this type of architecture are Intel x86 and IBM System/360 computers. In the article Understanding C by learning assembly, it's written that RBP and RSP are special-purpose registers (RBP points to the base of the current stack frame and RSP points to the top of the Jun 24, 2024 · Volume 1: Describes the architecture and programming environment of processors supporting IA-32 and Intel® 64 architectures. In windows, the GS register is used to manage thread-specific memory. As you may guess, r8 is an 8-bit register, and r/m8 can be either an 8-bit register or a byte from memory. Jun 21, 2015 · push eax ; Push the value of register eax onto the stack. X86-64 processors that support AVX incorporate 16 256-bit wide registers named YMM0–YMM15. The size of the general-purpose registers affects how much data the CPU can work with at once. CS107 x86-64 Reference Sheet Registers %rip Instruction pointer %rsp Stack pointer %rax Return value %rdi 1st argument %rsi 2nd argument %rdx 3rd argument %rcx 4th argument %r8 5th argument Win64 function parameters go in registers rcx, rdx, r8, and r9. Configuration flags of the Cr0 register. The debug registers allow programmers to selectively enable various debug conditions associated with a set of four debug Oct 22, 2020 · In this article, I would like to shortly describe the methods used to dump and restore the different kinds of registers on 32-bit and 64-bit x86 CPUs. Checks if the given string parameter is a valid x86 register (any size) in AT&T syntax. Originally, an SSE register could only be used as four 32-bit single precision floating point numbers (the equivalent of a float in C). This is a list of the various types of registers in the x86 architecture. Most have zero or one source operands and one source/destination operand, with the source operand coming first. The new registers also got their “narrow” versions. Many instructions on x86 (and other architectures, though less so) have some restrictions on how registers are supported. Double: The DX register is used to hold the high 16 bits of a 32-bit ("double word") value. You can assume that the C compiler will generate code that will be preserving rbx, rbp, rsi, rdi, and r12 thru r15. . All xmm0 registers are scratch. Most AVX instructions can use any of the XMM or YMM registers as SIMD operands. And registers almost always counted from zero, so RBX should be R3, and AX, CX, DX would be R0, R1, R2 respectively. In the second part, I would like to discuss the XSAVE family For more information, consult x86-64. x86 processors that have a protected mode, i. ) But as any other general purpose register, can be used to hold any other data. 2 RegistersModern 64-bit x86 processors have sixteen 64-bit general purpose registers, as de. Nov 6, 2021 · General purpose registers. The upper half of 64-bit registers is only accessible in 64-bit mode, unlike 32-bit registers which can be used in any mode on CPUs that support them. Contains the Page Fault Linear Address (PFLA). 32-bit x86 processors (starting with the 80386) also include various special/miscellaneous registers such as control registers (CR0 through 4, CR8 for 64-bit only), debug registers In this guide, we will limit our attention to more modern aspects of x86 programming, and delve into the instruction set only in enough detail to get a basic feel for x86 programming. The various SIMD units (SSE, AVX et cetera) have larger registers that are usable for a number of things, but there are only instructions for using them as 32-bit and 64-bit floating-point. I will explain how their values can be obtained via the ptrace(2) interface. edi is a register, a general purpose one which is generally used to hold the destination for string operations ( scas etc. e. Several operating systems such as Windows and Linux, use some of the segments for internal usage. x86-64 CPUs extend the integer registers to 64-bit: RAX is the full 64-bit value, with EAX and its sub-components mapped to the lower 32 bits. In AMD64/x86_64. Total size: 48 or 80 bits (4+2=6 Bytes or 8+2=10 Bytes) LDT and TR: 16 bits, as every other segment register. It has, among others, pages for GDT, IDT and The 64-bit x86 register set consists of 16 general purpose registers, only 8 of which are available in 16-bit and 32-bit mode. (Reference: Debian X32 Port page). Sep 30, 2010 · Note how our fish above use the 8A opcode. i r f: print all FPU floating registers (st0-7 and a few other f*) Other register groups besides a (all) and f (float) can be found with: maint print reggroups Oct 14, 2019 · A 64 bit x86 Linux machine, like NetRun: Call nasm like: nasm -f elf64 yourCode. Its Oct 23, 2018 · The best answer so far is this, which says that there are 40 registers in total. If your assembly code calls an external function, your code must pass arguments in the standard-conforming way, and it can depend upon the fact that, when the callee returns, preserved Apr 10, 2016 · 60. fyi/Arch1001 x86 (technically IA-32) Assembly Overview Registers, Flags, Memory Addressing, Instructions, Stack, Calling Conventions, Directives, Segments BIOS (Basic Input/Output System) + GDB (GNU Debugger) Design Review 3 level. x86とx64（またはAMD64と呼ばれる）は、IntelとAMDが開発した異なる命令セットアーキテクチャです。これらにはいくつかの主な違いがあります。 アドレス空間 x86アーキテクチャは32ビットのアドレス空間を持ち、通常4GBまでの物理メモリにアクセスできます。 Additional Control registers in Intel x86-64 series EFER. The linux kernel uses GS to access cpu-specific memory. 2003년 amd64를 지원하는 옵테론이 출시되고 이어서 2004년에 인텔이 프레스캇으로 em64t를 지원하면서 amd64는 사실상 x86 계열 아키텍처의 표준이 된다. But shoehorning that into x86 machine code (like AVX-512 did for vector regs), wouldn't be worth the code-size cost. org, it is a wiki about Operating System development. Its MSR number is 0xC0000080. 3. In computing, Streaming SIMD Extensions ( SSE) is a single instruction, multiple data ( SIMD) instruction set extension to the x86 architecture, designed by Intel and introduced in 1999 in their Pentium III series of central processing units (CPUs) shortly after the appearance of Advanced Micro Devices (AMD's) 3DNow!. Returns 1 if yes. When you use a register in an expression, you should add an at sign ( @ ) before the register. On the other hand, x64 processors, also known as 64-bit processors, can access a significantly larger memory space, theoretically up to 16 exabytes. The basic architecture of the x86-64 is described in Volume 1 of the System Developer’s Manual. Read more about Global Descriptor Table. Function parameters go in registers rdi, rsi, rdx, rcx, r8, and r9. Take certain double register multiply and divide instructions, for example, which specifically involve eax and edx in particular Dec 2, 2017 · I'm not sure about x86-64, but in the 8086 the AX register still was the only one that could be used for multiplication and division. ) Mar 10, 2024 · SSE, introduced by Intel in 1999 with the Pentium III, creates eight new 128-bit registers: XMM0 XMM1 XMM2 XMM3 XMM4 XMM5 XMM6 XMM7. x86-64 has 14 general-purpose registers and several special-purpose registers. Bit (s) Label. There is more extensive coverage on these topics in Chapter 3 of the B&O textbook. sub eax, [esp] ; Subtract the value of the memory at address esp from eax and store into eax. When running in 64bit mode, the number of general purpose registers is doubled (in addition to their size being doubled). This holds the segment of the code that is currently being You can watch this class without ads and with extra learning games, quizzes, and lab setup instructions by going to https://ost2. x86 assembly language is the name for the family of assembly languages which provide some level of backward compatibility with CPUs back to the Intel 8008 microprocessor, which was launched in April 1972. The PUSHA instruction is intended for use when the operand-size attribute is 16 and the PUSHAD instruction for when Guide to x86-64. Jan 22, 2020 · First and foremost, you have to use registers that support the instructions you want to use. YMM, because the YMM version would leave the upper lane not zeroed. is_reg8_intel Checks if the given string parameter is a valid x86 8-bit register in Intel syntax. 広義にはインテル以外のメーカー（ AMD など）の互換プロセッサを、さらに広義に Jun 19, 2019 · 39. This register becomes architectural in AMD64 and has been adopted by Intel. General purpose registers ( EAX, EBX, etc. See examples of declaring static data regions, using labels and arithmetic operations, and computing memory addresses. The core eight 16-bit registers are AX, BX, CX , DX, SI, DI, BP, and SP. 2. answered Jun 21, 2015 at 14:30. ) So the other major x86-64 calling convention does use more arg-passing registers. [1] [2] It is used to produce object code for the x86 class of processors. When the instruction is retired, the value of that dynamically allocated register is written back to whatever register currently holds the value of, say, RAX. Volume 2: Includes the full instruction set reference, A-Z. Pages 3-2 to 3-5 explain the various types of arguments you can specify on a MOV instruction. A 32-bit processor on x86 architecture has 32-bit registers, while 64-bit processors have 64-bit registers. Writing a 32-bit register zero-extends into the full 64-bit register, unlike writing low-8, high-8, or low-16 partial registers where the 8086 / 386 semantics still apply. Nov 30, 2022 · General Purpose Registers. In the x86 architecture, it is possible to access the individual 8-bit parts of the low 16-bit chunk of the EAX, EBX, ECX, and EDX registers. The x86 processor traces its heritage at least as far back as the In this guide, we will limit our attention to more modern aspects of x86 programming, and delve into the instruction set only in enough detail to get a basic feel for x86 programming. This differs from a load/store architecture (used That is, if your code changes a callee-preserved register, you are responsible for inserting instructions that save and restore the original register value. sequential numbers. By combining many flip-flops, the storage capacity can be extended to accommodate a huge number Guide to x86-64 A CS107 joint staff effort (Erik, Julie, Nate) x86-64 (also known as just x64 and/or AMD64) is the 64-bit version of the x86/IA32 instruction set. The register names are mostly historical in nature. When Intel expanded the x86 architecture to 32 bits in 1986, it doubled the size Registers are the fastest kind of memory available in the machine. For example, the instruction addq %rax, %rbx performs the computation %rbx := %rbx + %rax. You’ll notice different naming conventions, a side effect of the long history of the x86 architecture (the 8086 was first released in 1978). Jan 8, 2018 · Reading a YMM register is not logically different from reading an XMM register, but writing the low element (and leaving the other elements unmodified, like the poorly-designed vcvtsi2ss does) would be different for XMM vs. Application Programmers generally use only the general purpose registers, floating point registers, XMM, and YMM registers. The idea is to combine the smaller memory and cache footprint from 32-bit data types with the larger register set of x86_64. The first eight of these registers also have special names for historic reasons, they are, in order, rax, rbx, rcx, rdx, rsp, rbp, rsi, rdi. May 30, 2012 · In Windows 64-bit the GS register is used to point to operating system defined structures. The core eight 16-bit registers are AX, BX, CX, DX, SI, DI, BP, and SP. 29. x86-64 evolved out of 16-bit 8086, designed in 1979. Below is our overview of its features that are relevant to CS107. They are named r0, r1, r2, r3 … r15. Jun 14, 2024 · 1999년 amd에서 x86의 64비트 확장인 amd64를 발표한다. Given the expanded register set, x64 uses the __fastcall calling convention and a RISC-based exception-handling model. On DOS and up to 32-bit Windows, you can run a very handy program called "debug. The following diagram is taken directly from Chapter 3 in this volume: Registers. To hold these segment bases, they included Segment Registers: CS The Code Segment register. General Purpose Registers Nov 30, 2020 · General-purpose registers. an Intel i7). Learn the basics of 32-bit x86 assembly language programming, covering registers, memory and addressing modes, and instructions. 1. As in Real Mode, A is the segment part and B is the offset within that segment. mov rcx,'H' ; function parameter: one char to print. It also means that complex special-purpose instructions will predominate. This at sign tells the debugger that the following text is the name of a register. amd64의 전체 사양은 2000년 8월에 공개되었다. And that, folks, was a quick history of x86 accumulator! From an 8-bit A of 8008, to 16-bit AX of 8086, to 32-bit EAX of 80386, to 64-bit RAX. Additionally, I Mar 19, 2021 · In computer engineering, a register–memory architecture is an instruction set architecture that allows operations to be performed on (or from) memory, as well as registers. The x86 architecture supports segmentation. Registers are the fastest kind of memory available in the machine. The first part will focus on General Purpose Registers, Debug Registers and Floating-Point Registers up to the XMM registers provided by the SSE extension. These are all 16 bits wide. This handout only mentions a small subset of the rich possibilities provided by the x86-64 instruction set and architecture. Oct 23, 2017 · MM registers are the registers used by the MMX instruction set, one of the first attempts to add (integer-only) SIMD to x86. For example, RAX used to be EAX (in the 32-bit machine), which used to be called the . 7. Feb 26, 2022 · The 64-bit versions of the 'original' x86 registers are named: The registers added for 64-bit mode are named: These may be accessed as: Usage during syscall/function call: First six arguments are in rdi, rsi, rdx, rcx, r8d, r9d; remaining arguments are on the stack. edited Aug 25, 2016 at 18:54. FS and GS are commonly used by OS kernels to access thread-specific memory. Apr 8, 2024 · The original x86 family members had a separate math coprocessor that handled floating point arithmetic. A register is a collection of flip-flops, Single bit digital data is stored using flip-flops. A register-transfer level (RTL) description of a 8-bit register with detailed implementation, showing how 8 bits of data can be stored by using Flip-flops. (Windows x64 passes the 5th arg on the stack, even if it's FP and the first 4 args were all integer. This register becomes architectural in AMD64 and has been adopted by Intel as IA32_EFER. The instruction decoder allocates a register from a big bank of registers. Mar 29, 2024 · The primary discrepancy between x86 and x64 architectures lies in their memory-addressing capabilities. But if I add that up, I get 48. The registers found on the 8086 and all subsequent x86 processors are the following: AX, BX, CX, DX, SP, BP, SI, DI, CS, DS, SS, ES, IP and FLAGS. extern putchar. Could anybody provide an official answer on how many registers an x86_64 CPU has (e. Registers x86-64 “General Purpose” Registers Many “general purpose” registers have special purposes and conventions associated such as Return Value: %rax / %eax / %ax Function Args 1 to 6: %rdi, %rsi, %rdx, %rcx, %r8, %r9 Stack Pointer (top of stack): %rsp Old Code Base Pointer: %rbp, historically start of current stack frame but is May 2, 2016 · The FPU (Floating-Point Unit) has registers for 80-bit floating-point values (in an Intel format that is the IEEE 754 format with slight changes). Writing an 8 or 16-bit partial register doesn't zero-extend to the rest of the register. The least significant 8 bits of the first four of these registers are accessible via the AL, BL , CL, and DL in all execution modes. Update: Intel has just introduced a new extension for x86-64 called APX which adds 16 more registers named r16-r31. See also Sep 15, 2019 · The registers on a 64 bit CPU are 64 bits wide. You can also take a look at wiki. exe" from a DOS shell, which is very useful for learning about 8086. The registers in protected mode are limited to 32 bits. 8. The following notation is used to address a byte within a segment: Segment-register:Byte-address. Later variants integrated the FPU into the microprocessor itself. Nov 14, 2018 · By comparison, the x86-64 System V ABI passes the first 6 integer args in registers, and the first 8 FP args in XMM0. You should only need to save and restore rax, rcx, rdx, and r8 thru r11. The least significant 8 bits of the first four of these registers are accessible via the AL, BL, CL, and DL in all execution modes This is part two of the ARM Assembly Basics tutorial series, covering data types and registers. Instructions which access memory can use segment register based addressing mode. The 64-bit x86 register set consists of 16 general purpose registers, only 8 of which are available in 16-bit and 32-bit mode. x32 can provide up to about 30% reduction in memory usage and up to about 40% increase in speed. OS X in 64 bit uses the same parameter scheme. A register serves as a quick memory for accepting, storing, and sending data and instructions that the CPU will need right away. Contains various control flags that enable architectural extensions, and indicate support for specific processor capabilities. There are eight 16-bit general-purpose registers: AX, BX, CX, DX, BP, SI, DI, and SP; and you can place any value in them that may be expressed in 16 bits or fewer. Registers. The ESI, EDI, EBX, EBP, ESP are call-preserved whereas EAX, ECX and EDX are not call-preserved. 32-bit operand-size is the default in x86-64 machine code, no prefixes required. Some flags can be set or cleared directly with specific instructions: For reading and writing the sign, zero, auxiliary carry, parity, and carry flags, you can use LAHF to load the lower 8 bits (those 5 flags plus 3 indeterminate bits) into the AH register, and you can use SAHF to store those values from AH back into the flags register. In addition to the registers being used for mass operations, they are useful for their property of being preserved through a function call (call-preserved) in 32-bit calling convention. Win64 functions assume you've allocated 32 bytes of stack space to store the four parameter registers, plus another 8 bytes to align the stack to a 16-byte boundary. Most of the work of a CPU is to process data. Regarded as a programming language, assembly is machine-specific Jul 10, 2023 · Extended Feature Enable Register (EFER) is a model-specific register added in the AMD K6 processor, to allow enabling the SYSCALL/SYSRET instruction, and later for entering and exiting long mode. Feb 3, 2012 · The architecture name is addressed as x86 in general, or occasionally x86-64. 32 bits can represent any integer between 0 and 4 GiB. Apr 24, 2023 · Intel IA-32 Chunks of General-Purpose Registers. For syscalls, the syscall number is in rax. x86 debug register. SSE2 expanded the capabilities of the XMM registers, so they can now be used as: Dec 7, 2023 · 16-bit. But scalar with ymm doesn't exist in the machine-code Sep 19, 2015 · x32 is an ABI for amd64/x86_64 CPUs using 32-bit integers, longs and pointers. It also introduces a new naming convention that must be used for these new registers and can also be used for the old ones (except that AH, CH, DH and BH have no equivalents). Take R15, for example: ⁂. In the 64 bit x86 architecture there are 16 general purpose registers registers. In a register–memory approach one of the operands for ADD operation may be in memory, while the other is in a register. The original coprocessor was the 8087, and all FPU s since have been dubbed “x87” chips. For example 21. The %rip register on x86-64 is a special-purpose register that always holds the memory address of the next instruction to execute in the program's code segment. The real encoded order is AX, CX, DX, BX (See Why are first four x86 GPRs named in such unintuitive order? ). In general, forget about "types" in assembly: assembly is not a typed language, or better any data is just bytes. osdev. The register names are mostly historical. Apr 21, 2022 · Two important differences between x86 and x64 are: 64-bit addressing capability; Sixteen 64-bit registers for general use. Volume 3: Includes the full system programming guide, parts 1, 2, 3, and 4. Register Types. All of this also applies to EBX/RBX, ECX/RCX, and The value pushed for the ESP or SP register is its value before prior to pushing the first register (see the “Operation” section below). Mar 25, 2011 · i r: print all register except floating point & vector register (xmm, ymm, zmm). Also, see how to check for overflow and handle it in C++ and assembly code. For a more complete (but still readable) introduction, consult The AMD64 Architecture Programmer’s Manual, Volume 1: Application Programming. Nayuki. Linux 64 floating-point parameters and return values go in xmm0. takes value inside register %eax, adds 4 to it, and then fetches the contents of memory at that address, putting the result into register %ebx; sometimes called a "load" instruction as it loads data from memory into a register arithmetic two operand instructions addl src,dst dst = dst + src subl src,dst dst = dst - src imull src,dst dst = dst * src The 64-bit versions of the 'original' x86 registers are named: The registers added for 64-bit mode are named: These may be accessed as: Usage during syscall /function call: First six arguments are in rdi, rsi, rdx, rcx, r8d, r9d; remaining arguments are on the stack. Bit 13 indicates that the next instruction in the instruction stream accesses one of the debug registers. Streaming SIMD Extensions. Controls cache settings for the highest-level page table. There are six debug registers, named DR0 DR7, with DR4 and DR5 as obsolete synonyms for DR6 and DR7. Sep 8, 2023 · SIMD Registers. asm. On the x86 architecture, a debug register is a register used by a processor for program debugging. The low-order 128 bits of each YMM register are aliased to a corresponding XMM register as illustrated in Figure 7-15. The data types we can load (or store) can be signed and unsigned words, halfwords, or bytes. So, in practice the segment registers in protected mode are used to store indexes to the GDT. These instructions perform computation on values, typically values stored in registers. of x86 programming, and delve into the instruction set only in enough detail to get a basic feel for programming x86 compatible chips at the hardware level. It usually reflects the result of arithmetic operations as well as information about restrictions placed on the CPU operation at the current time. Guide to x86-64. Registers Modern (i. bp wq fm hi pi mv si rd zm pa