Question

With online help, I was able to write nasm code in Mac OS X resulting in an executable that prints its own filename, argv[0] in equivalent C code. When I use the same code in Windows, I want it to print the programs name:

C:\> nasm -f win32 -o scriptname.obj scriptname.asm
C:\> golink /fo scriptname.exe scriptname.obj /console kernel32.dll Msvcrt.dll

GoLink.Exe Version 0.27.0.0 - Copyright Jeremy Gordon 2002/12 - [e-mail]
Output file: scriptname.exe
Format: win32 size: 2,048 bytes
C:\> scriptname.exe
Program: scriptname.exe

But what it actually prints is emptiness:

C:\> scriptname.exe
Program: 

Specs:

• golink 0.27.0.0
• nasm 2.10.05
• Windows 7 Professional x64
• MacBook Pro 2009

Answer 1

You call GetStdHandle and save the returned value to ecx, ecx is a volatile register, the value will not be saved across calls unless you push/pop it. Your first call to WriteConsoleA uses it and clobbers it so the next call, ecx is not what you expect.

* EDIT *
I was bored so here is working code:

[bits 32]

section .data

program db "Program: ", 0
programlen equ $-program

nl db "", 13, 10, 0
nllen equ $-nl

section .bss

buf resd 1
argc resd 1
argv resb 255

section .text

global Start
extern GetStdHandle
extern __getmainargs
extern WriteConsoleA
extern ExitProcess

strlen:             ; eax: a string ending in 0
push eax            ; cache eax

.strloop:

mov bl, byte [eax]
cmp bl, 0
je .strret          ; return len if bl == 0
inc eax             ; else eax++
jmp .strloop

.strret:

pop ebx             ; ebx = cached eax
sub eax, ebx        ; eax -= ebx
ret                 ; eax = len

Start:

push 0
push buf
push argv
push argc
call __getmainargs
add esp, 16         ; clear stack (4 * 4 arguments)

push -11            ; get stdout
call GetStdHandle
mov esi, eax
add esp, 4          ; clear stack (4 * 1 argument)

push 0              ; null
push buf            ; [chars written]
push programlen
push program
push esi            ; stdout
call WriteConsoleA
add esp, 20         ; clear stack (4 * 5 arguments)

mov edx, [argv]
mov eax, [edx]   ; <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
call strlen
push 0              ; null
push buf            ; [chars written]
push eax            ; len argv[0]
push dword [edx]    ;<<<<<<<<<<<<<<<<<<<<<<<<<<<<       ; argv[0]
push esi            ; stdout
call WriteConsoleA
add esp, 20         ; clear stack (4 * 5 arguments)

push 0              ; null
push buf            ; [chars written]
push nllen
push nl
push esi            ; stdout
call WriteConsoleA
add esp, 20         ; clear stack (4 * 5 arguments)

push 0
call ExitProcess


D:\NASM Projects\ReadArgs>ReadArgs.exe
Program:  ReadArgs.exe

D:\NASM Projects\ReadArgs>