file format elf64-x86-64 Disassembly of section .text: 0000000000000000 : 0: f3 c3 repz retq So, repz is a prefix that repeats the following instruction until some register is 0. Also, it only So what on earth is gcc doing generating a repz retq?В длинном (64-разрядном) режиме вы возвращаете ( ret ), выбирая четвертый адрес из стека в %rip . В 32-битном режиме вы возвращаете ( ret ) After studying assembly code, here are my thoughts, let's look at a sample: fun: push %rbp mov %rsp,%rbp pop %rbp retq main: callq 18 Feb 2017 This reference is intended to be precise opcode and instruction set reference (including x86-64). Its principal aim is exact definition of x64 assembly code uses sixteen 64-bit registers. Additionally, the example, moving a quadword from %rax to %rbx results in the instruction movq %rax, %rbx. 27 Feb 2016 Let's look at the assembly instructions for this program: Simple Function: it only has 4 kinds of instructions in it, push , pop , mov , and retq . memory there is split up into 8 byte (64 bit) chunks that represent the current stack. 12 Sep 2012 Now let's use the disassemble command to show the assembly instructions for the pop %rbp 0x0000000100000f74 : retq End of assembler dump. As x86 moved from 16-bit to 32-bit to 64-bit, the registers were 1 Answer. In long (64-bit) mode, you return ( ret ) by popping a quadword address from the stack to %rip . In 32-bit mode, you return ( ret ) by popping a dword address from the stack to %eip . Some tools like objdump -d call the first one retq . x86-64 (also known as just x64 and/or AMD64) is the 64-bit version of the x86/IA32 .. cleans up the stack, and use retq instruction to return control to the caller. 16 Feb 2016 So I've been doing a fair amount of x86-64 programming lately. . a function that is jumped to by PyObject_Malloc , a retq instruction will be hit.