Thread: Mixing C and Assembly

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

Should be something like:

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

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