CODEWITHSUNDEEP
assemblywinapix86nasm
prog
prog

Reputation: 150

undefined reference to WinMain@16

segment .data

msg db "Enter your ID", 0xA, 0xD
len equ $ - msg

segment .bss

id resb 10

segment .text

global _start

_start:

    mov eax, 4
    mov ebx, 1
    mov ecx, msg
    mov edx, len
    int 0x80

    mov eax, 3
    mov ebx, 0
    mov ecx, id
    mov edx, 10
    int 0x80

    mov eax, 4
    mov ebx, 1
    int 0x80

_exit:

    mov eax, 1;
    xor ebx, ebx
    int 0x80

    ;End

I am trying to compile this file in c using gcc, but the program gives me an error and I have absolutely no idea where the problem is. Does it have anything to do with my OS?

Upvotes: 6

Views: 7369

Answers (4)

user1911887
user1911887

Reputation: 113

This program will work only in 32 bit Linux . Still there are issues in this program.

Change _start to main Also, ecx and edx might not be preserved after a system call (int 0x80)

Please try the below example.

Assemble & link with:

nasm -felf hello.asm
gcc -o hello hello.o

code:

segment .data
msg db "Enter your ID", 0xA
len equ $ - msg

segment .bss
id resb 10

segment .text
global main

main:
    mov eax, 4
    mov ebx, 1
    mov ecx, msg
    mov edx, len
    int 0x80

    mov eax, 3
    mov ebx, 0
    mov ecx, id
    mov edx, 10
    int 0x80

    mov edx, eax  ;; length of the string we just read in.
    mov eax, 4
    mov ebx, 1
    mov ecx, id
    int 0x80

_exit:

    mov eax, 1;
    xor ebx, ebx
    int 0x80

    ;End

Upvotes: 3

user2624583
user2624583

Reputation: 54

I know this is an old thread, but I have this issue all the time and want to clarify it.

You need to change _start to _main. I believe this is so NASM can assemble your file correctly, replacing references to WinMain@16 with _main so that MinGW can link it successfu

Also, int 0x80 is a LINUX system call. Perhaps use call _printf instead, and put extern _printf at the top of your program.

Upvotes: 1

user1911887
user1911887

Reputation: 113

For Windows, if you are OK to use C libraries, try this example.

;;Assemble and link with
;nasm -fwin32 hello.asm
;gcc -o hello hello.obj

global _main 
extern _scanf 
extern _printf     

segment .data

    msg: db "Enter your ID", 0xA, 0xD, 0  ; note the null terminator.
    formatin: db "%s", 0                  ; for scanf.

segment .bss
    id resb 10

segment .text

_main:

   push msg
   call _printf
   add esp, 4 

   push id  ; address of number1 (second parameter)
   push formatin ; arguments are pushed right to left (first parameter)
   call _scanf
   add esp, 8 


   push id
   call _printf
   add esp,4              

   ret

Upvotes: 1

Anton Kovalenko
Anton Kovalenko

Reputation: 21507

Your code is not supposed to use standard C library, so linking it with bare ld instead of gcc would help (_start is the entry point by default, other one can be specified with --entry option for ld).

But it won't help: this code is not for Windows OS, and you're obviously compiling it for Windows.

Upvotes: 0

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