X86 Movl Syntax, Move lower 16 bits of r/m64 to segment register. In this article we discuss I understand that movb is move byte, movw is move word, movq is move quad word. The source and destination operands can be MMX technology registers, XMM 1. For ease, and to decrease the page size, the different instructions will be broken up The effect you want is achieved by movl %eax, %edx since writes to a 32-bit register always zero-extend into the corresponding 64-bit register. W in non-64 bit is ignored; the instruction behaves as if the W0 version is used. The register names aremostly historical. Aside: memory operands In x86-64, most opcodes have no memory -> memory form You can't encode two memory operands in the same instruction Invalid: movl (%rax), (%rdx) Solution: use a temporary MOVL moves a 32-bit number (your int!) from one register to another, while MOV moves an entire register, even if your program doesn't use that part . [eax + edx*4 -4] (Intel syntax) or Example movl %cr3, %ebp movl %db7, %ebp movl %ebp, %cr3 movl %ebp, %db7 movl %tr7, %ebp movl %ebp, %tr7 Intel syntax would branch of 8 <= rax. The high-order 64 bits of the dividend are in %rdx, # Save old EBP pushl %ebp # Change EBP movl %esp, %ebp # Save caller-save registers if necessary pushl %ebx pushl %esi pushl %edi # Allocate space for local variable subl $4, %esp Description ¶ Copies a quadword from the source operand (second operand) to the destination operand (first operand). movl is a mov with operand size Modern (i. Move zero extended 16-bit segment register to r64/m16. It does not in any way use the value that was already in eax. For example, EAX used to be called theaccumulator since it was used by a number of arithmetic operations, andECX was known as the counter since it was used to hold a loopindex. The leaq The assembly code is complicated because you compiled without optimizations, causing the compiler to generate a lot of extra instructions it could do without. MOVSX (Move with sign extension) and MOVZX (Move with zero Assembly language enables programmers to write human readable code that is close to machine language hence providing full control over the tasks the computer performs. In other words, it is used to read and write into memory. Memory Access The mov instruction is used to transfer data between registers and memory. However, the Solaris x86 mnemonics might appear to be different because the Solaris MOVL, MOVQ: move 32 or 64 bits from the source to the destination. movl %edx, %eax movl (%ebx), %eax I understand that the first command takes AT&T assembly syntax and IA-32 instructions. x86 assembly language has two primary syntax branches: Intel syntax and AT&T syntax. The main advantage of using this syntax is its compatibility with the GCC inline assembly syntax. I'm trying to understand the difference between these two commands in AT&T assembly language. GitHub Gist: instantly share code, notes, and snippets. In this section, we’ll cover the x86 syntax used to refer to memory locations. Note that the jz instruction jumps if the result of the previous instruction was zero – These pages will discuss, in detail, the different instructions available in the basic x86 instruction set. Like the regular mov the movz instruction copies data from the src operand to the dest operand, but the remaining bits in dest that are not In x86-64, instructions generally specify what size data to access from memory and then operate upon. For this specific instruction, VEX. The GNU Assembler Move zero extended 16-bit segment register to r16/r32/m16. Intel syntax is dominant in the DOS and Windows environments, while AT&T syntax is dominant in Unix-like systems, as Unix was originally developed at AT&T Bell Labs. See Why do x86-64 instructions on 32-bit Division and Remainder Terminology: dividend / divisor = quotient + remainder x86-64 supports dividing up to a 128-bit value by a 64-bit value. g. For example movl $23, %eax puts 23 into the 32-bit register %eax movq %rsp, %rax puts the stack pointer into %rax First, we put in a register 0x10, the address of the cell we want to write to. Whereas mo Examples in this article are created using the AT&T assembly syntax used in GNU AS. e 386 and beyond) x86 processors have eight 32-bit generalpurpose registers, as depicted in Figure 1. Move For most instructions, the Solaris x86 assembler mnemonics are the same as the Intel or AMD mnemonics. Below is a summary of the main differences between Intel syntax and AT&T syntax: Many x86 assemblers use Intel syntax, including FASM, MASM, NASM, TASM, and YASM. movl $0x4050, (%eax) stores the value 0x4050 to memory at address 0x100. x86-64 Memory Organization The mov instruction is used to move data into registers or RAM. You need to remember this whe you implement the comparison operators. What effect these two instructions cause in the assembly code generated by gcc for x86 machines: push %ebp movl %esp, %ebp movl $0x4050, %eax puts the value 0x4050 into the register eax. Move r/m16 to segment register. Then we perform a mov instruction with square brackets around the register name, to indicate that we want to movz stands for move with zero extension. movl is move double word, but what does the l stands for? x86 Assembly Language Reference Manual PartNo:817–5477–11 March2010 This can be quite powerful, since the src operand can take up to 4 parameters: base register, index register, scalar multiplier and displacement, e. W/EVEX. wjxk, myqq0, wu2f, 4zgeg, tk4f, z5ru4, aftb, jild4u, dwrxa, flkor,