macOS Calling C-functions from assembly

[Flybro]

Hi,

I'm trying to compile small assembly routine (nasm) which print a message to the console using the puts c-function.
Unfortunately every time I try to compile it, I get "undefined symbol". If I replace "puts" with "_puts" then program compile without any errors or warnings but when I try run it "segementation fault" occurs.

nasm -f macho eatclib.asm
gcc -arch i386 -o eat eatclib.o

Undefined symbols:
  "puts", referenced from:
      _main in eatclib.o
ld: symbol(s) not found
collect2: ld returned 1 exit status

[SECTION .data]
	
	EatMsg: 		db "Eat at Joe's!",0	
	
[SECTION .bss]
		
[SECTION .text]
	
	extern puts
	global _main
	
_main:
	push	ebp
	mov	ebp,esp
	push	ebx
	push	esi
	push	edi
	push	EatMsg
	call	puts
	add 	esp,4
	pop 	edi
	pop 	esi
	pop 	ebx
	mov 	esp,ebp
	pop 	ebp
	ret

gcc -v

Using built-in specs.
Target: i686-apple-darwin10
Configured with: /var/tmp/gcc/gcc-5646.1~2/src/configure --disable-checking --enable-werror --prefix=/usr --mandir=/share/man --enable-languages=c,objc,c++,obj-c++ --program-transform-name=/^[cg][^.-]*$/s/$/-4.2/ --with-slibdir=/usr/lib --build=i686-apple-darwin10 --with-gxx-include-dir=/include/c++/4.2.1 --program-prefix=i686-apple-darwin10- --host=x86_64-apple-darwin10 --target=i686-apple-darwin10
Thread model: posix
gcc version 4.2.1 (Apple Inc. build 5646) (dot 1)

 

[Sydde]

Just guessing here, does puts return an int?

 

[autorelease]

The reason why "call puts" doesn't work is probably because nasm doesn't understand GCC's name mangling. (All functions in libc actually have underscores before their names.) "call _puts" should work, but I don't remember enough x86 assembly to figure out why you're getting a segfault.

Yes, puts does return an int, but it's in eax, so that shouldn't have any effect.

Also, if you don't want to use nasm, assembly files can be passed right into GCC, and you won't have to worry about name mangling issues. Use the .S extension (capital S, that's important.) GCC will link everything together properly. Example:

gcc -o output file1.c file2.c file3.S

You'll have to use AT&T syntax, but if I recall correctly there's some switch that lets you use Intel syntax.