Introduction To 64 Bit Windows Assembly Program... -

RAX, RBX, RCX, RDX: The primary data registers. RAX is typically used for return values.

; External Windows functions extern GetStdHandle extern WriteFile extern ExitProcess section .data msg db "Hello, 64-bit World!", 0 msg_len equ $ - msg section .bss bytes_written resq 1 section .text global main main: sub rsp, 40 ; Reserve shadow space + align stack ; Get handle to standard output mov rcx, -11 ; STD_OUTPUT_HANDLE call GetStdHandle mov r12, rax ; Save handle in r12 ; Write to the console mov rcx, r12 ; Arg 1: Handle lea rdx, [rel msg] ; Arg 2: Buffer address mov r8, msg_len ; Arg 3: Length lea r9, [rel bytes_written] ; Arg 4: Pointer to written count mov qword [rsp + 32], 0 ; Arg 5: Overlapped (on stack) call WriteFile ; Exit the program xor rcx, rcx ; Return code 0 call ExitProcess Use code with caution. Copied to clipboard

Shadow Space: Even if a function takes fewer than four arguments, the caller must reserve 32 bytes of "shadow space" on the stack before making the call. This space allows the called function to save those four register-based arguments if necessary. Introduction to 64 Bit Windows Assembly Program...

The shift from 32-bit (x86) to 64-bit (x64) architecture introduced several significant changes. The most obvious is the expansion of general-purpose registers from 32 bits to 64 bits. Furthermore, the number of available registers doubled, and the calling convention—the way functions receive arguments—was standardized. In 64-bit Windows, the system uses a specific "fast call" convention that utilizes registers instead of the stack for the first few arguments, greatly increasing execution speed. The x64 Register Set

In this snippet, we observe the application of the calling convention: RCX , RDX , R8 , and R9 are loaded with arguments before the WriteFile call, and the stack is adjusted to accommodate the shadow space. Conclusion RAX, RBX, RCX, RDX: The primary data registers

Introduction to 64-Bit Windows Assembly Programming Assembly language provides the most direct link between a programmer and the computer hardware. While high-level languages like C++ or Python handle memory management and hardware interfacing automatically, 64-bit Windows Assembly (x64) requires you to manage every register and memory address manually. Learning x64 assembly on Windows is essential for reverse engineering, performance optimization, and understanding the inner workings of the operating system. The Transition from 32-bit to 64-bit

To write a program, you typically use an assembler like NASM (Netwide Assembler) or MASM (Microsoft Macro Assembler). Below is a conceptual look at what a "Hello World" program looks like using the Windows API function WriteFile . Copied to clipboard Shadow Space: Even if a

RBP, RSP: Pointer registers. RSP is the stack pointer, while RBP is the base pointer.