C enums have integer type-kind. Additional arguments are pushed onto the stack (right to left). The stack must be kept 16-byte aligned. CONTEXT Structure Alignment. Space is allocated on the call stack as a shadow store for callees to save those registers. You merely allocate the space in your prologue and it's good for the whole function. And the calling "conventions" of the Microsoft compiler has almost become a de factostandard for the Windows operating system. To understand this better, we will dissect the information in junks starting with arguments/parameters. times you need to use this calling convention is when you either call a function in the Windows API, or you call a function written in C or C++. There is a strict one-to-one correspondence between a function call's arguments and the registers used for those arguments. It uses registers RCX, RDX, R8, R9 for the first four integer or pointer arguments (in that order), and XMM0, XMM1, XMM2, XMM3 are used for floating point arguments. Stack and Structure alignment. You know that the caller has (according to the calling convention) taken care of its stack alignment and . This provides a way to be sure that when entering a function (that is, after a call instruction), the value of the stack pointer is always 8 modulo 16. PDF 5. Calling conventions - Agner Calling conventions - osdev.wiki 18.1 C Datatypes and Alignment . How did we know the argument to puts was supposed to go in RDI? The called procedure assumes that the stack has room to store four 64-bit registers and that the address contained in RSP (stack pointer) is 16 byte aligned. On the other hand C.ADDI16SP instruction assumes the stack pointer is kept 16-byte aligned and is useless if the stack pointer is not 16-byte aligned. Most of the time, 8 bytes works fine; this happens pretty often when working with ROP chains. This space can be left uninitialized, it doesn't matter. __regcall . Stack frame layout on x86-64 - Eli Bendersky's website 64 Bit Linux machine use AMD 64 System V Application Binary Interface for their calling conventions. Shellcode: Dual mode PIC for x86 (Reverse and Bind Shells for Windows) Another important difference is the way functions are called, the calling convention. It is the caller's job to clean the stack. Microsoft x64 The x64 Application Binary Interface [ 1] (ABI) uses a four-register fast-call calling convention by default. Calling Conventions Computer Systems Section 3.7. In Assembly Language, Seventh Edition for x86 Processors by Kip Irvine, on page 211, it says under 5.53 The x86 Calling Convention which addresses the Microsoft x64 Calling Convention, When calling a subroutine, the stack pointer ( RSP) must be aligned on a 16-byte boundary (a multiple of 16). What is the 'shadow space' in x64 assembly? - newbedev.com About the x64 stack Alignment - Intel Community Function calling conventions. Functions that allocate stack space, call other functions, save non-volatile registers or use exception handling are called " frame functions "; other functions are called " leaf functions ".. Frame functions use an area on the stack called a " stack frame " and have a defined prologue in which this is set up. [Bug target/54412] minimal 32-byte stack alignment with -mavx on 64-bit Windows. Windows Assembly Languages - McDermott Cybersecurity x64 calling convention | Microsoft Docs In fact, aside from the x64-specific parts of the x64 calling convention, you can think of the x64 calling convention as a logical extension of __fastcall that is designed to take advantage of the expanded register set available with x64 processors. 1. x86-64 calling conventions. If the return value is an integer/struct/union whose size is less than or equal than 64 bits, . " from "Unwindability" clause on Overview of x64 Calling . 1.1. A nice diagram of the stack and where 16-byte alignment occurs appears here in the YASM manual, 15.2 win64 Structured Exception Handling, as well as other information on x64 calling convention. Many iOS diverges from Procedure Call Standard for the ARM 64-bit Architecture in several ways, as described here. This will specify a 64 bit code, with a . But this code is working only in registers, and code alignment issues are the same in 32 and 64 bit mode. The Windows x64 ABI (Application Binary Interface) presents some new challenges for assembly programming that don't exist for x86. But I'd really suggest just not defining them at all. x64 Assembly - Brent's Website A function calling this needs to have at least 32 bytes of stack to store the parameters and align the stack upon call. It is meant to be used to make debugging x64 easier. FuncFrame doesn't know anything about function's arguments or return values, . . Differences in various implementations include where parameters, return values, return addresses and scope links are placed (registers, stack or memory etc.