Mixing C and Assembly

I'm using NASM and GCC (Assembly and C) compilers and I'm trying to make a function ad.asm in assembly and link it with my main.c by using the following commands:
nasm -f coff ad.asm
gcc -Wall -o main.exe main.c ad.o

and I get the following error message:
D:\Hwk3\Task2>gcc -Wall -o main.exe main.o ad.o
main.o(.text+0x63):main.c: undefined reference to `ad'
collect2: ld returned 1 exit status

Here's my code, can anyone tell me what I'm doing wrong?
main.c

Code:

#include <stdio.h>

int ad(int,int);

int main(int argv, char *argc[])
{
	int a,b,total;
	printf("Enter two integers");
	scanf("%i %i", &a, &b);
	total=ad(a,b);
	printf("The sum of %i + %i = %i",a,b,total);
	return 0;
}

ad.asm

Code:

ad:
	push ebp
	mov ebp,esp
	mov eax,[ebp+8]
	mov ebx,[ebp+12]
	add eax,ebx
	mov esp,ebp
	pop ebp
	ret

Your compiler is looking for int ad() within the file.


extern "C" int ad(int,int)


should clear the error up.


The body of your function lies outside of the current module therefore you must declare it with extern.

Do I need that "C" as well? Because I tried both and it didn't work.

Implement ad() in the C program as C code, then compile it with
gcc -S prog.c
Examine prog.s to find out exactly what ad() is called - it may have a leading underscore for example.

Then adjust the name in your asm file.

Okay, I was wrong, that didn't fix anything. Here's my code now:

_ad.asm

Code:

;add.asm - function of main.c adds two given variables and returns answer
;Andy Gearhart
;Nov 13, 2003
_ad:	push ebp
	mov ebp,esp
	mov eax,[ebp+8]
	mov ebx,[ebp+12]
	add eax,ebx
	mov esp,ebp
	pop ebp
	ret

main.c

Code:

*
Program Name: main.c 
Description: Adds 2 ints using an Assembly function
Programmer: Andy Gearhart
*/
#include <stdio.h>
 int ad(int,int);

int main(int argv, char *argc[])
{
	int a,b,total;
	printf("Enter two integers");
	scanf("%i %i", &a, &b);
	total=ad(a,b);
	printf("The sum of %i + %i = %i",a,b,total);
	return 0;
}

Here's the error message I get:
D:\Hwk3\Task2>gcc -Wall -o main.exe main.c _ad.o
d:/djgpp/tmp\cchG8Zlv.o(.text+0x6e):main.c: undefined reference to `ad'
collect2: ld returned 1 exit status

gcc supports inline asm, as I recall.

Should be something like:

; main.asm
global _ad
; ...
section .text
; ...
_ad:
; ...

/* main.c */
extern int ad(int, int);
/* ... */