I was trying to compile a simple assembly program in Mac OS X (Leopard).
I was getting an error message
ld: could not find entry point “_start” (perhaps missing crt1.o) for inferred architecture i386
A simple asm program for FreeBSD and MacOS
(we have to use the stack for system call, from http://asm.sourceforge.net//howto/Assembly-HOWTO.rtf)
section .text
global _start ;must be declared for linker (ld)
_syscall:
int 0x80 ;system call
ret
_start: ;tell linker entry point
push dword len ;message length
push dword msg ;message to write
push dword 1 ;file descriptor (stdout)
mov eax,0x4 ;system call number (sys_write)
call _syscall ;call kernel
;the alternate way to call kernel:
;push eax
;call 7:0
add esp,12 ;clean stack (3 arguments * 4)
push dword 0 ;exit code
mov eax,0x1 ;system call number (sys_exit)
call _syscall ;call kernel
;we do not return from sys_exit,
;there's no need to clean stack
section .data
msg db "Hello, world!",0xa ;our dear string
len equ $ - msg ;length of our dear string
In Mac OS X we should use format macho
nasm -f macho hello.asm
and for the linker (we need to specify the entry point)
ld -e _start -o hello hello.o
resources:
http://asm.sourceforge.net//howto/Assembly-HOWTO.rtf
http://zathras.de/angelweb/blog-intel-assembler-on-mac-os-x.htm