- 1 year ago
"Hello world" in x64 assembly for Windows - Shadow space / Stack alignment
Sure! Here's an example of a "Hello world" program in x64 assembly for Windows that includes the proper handling of the shadow space and stack alignment:
asmsection .data
message db 'Hello, world!',0
section .text
global _start
_start:
; Prologue
sub rsp, 40 ; Allocate shadow space and align stack
; Print the message
mov rdx, message ; Address of the message
mov rcx, 0 ; Null-terminated string
call printf ; Call the C library printf function
; Epilogue
add rsp, 40 ; Restore stack
xor eax, eax ; Return 0
ret
section .data
extern printf ; External declaration of printf function
In this assembly code:
The
message
variable is defined in the.data
section and contains the string "Hello, world!" followed by a null terminator.The
_start
label is the entry point of the program.In the prologue, we allocate 40 bytes on the stack to accommodate the shadow space and align the stack to a 16-byte boundary. This ensures proper stack alignment as required by the x64 calling convention.
The address of the
message
variable is loaded into therdx
register as the first argument to theprintf
function.The
rcx
register is set to 0 to indicate that the string is null-terminated.The
printf
function is called.In the epilogue, we restore the stack by adding 40 bytes, clean up the shadow space and other temporary data, and then return 0.
The
.data
section includes an external declaration for theprintf
function.
To assemble and link the code, you can use an assembler such as NASM and a linker such as GNU ld. Here's an example of the command to assemble and link the code using NASM and ld:
shellnasm -f win64 hello.asm -o hello.obj
ld hello.obj -o hello.exe -lmsvcrt
After assembling and linking the code, you can run the resulting hello.exe
executable to see the "Hello, world!" message printed on the console.
Note that the printf
function is linked from the C runtime library (msvcrt
).