gcc - link c and assembly -


i have simple main.c file:

#include <stdio.h> int cnt; extern void increment(); int main() {     cnt = 0;     increment();     printf("%d\n", cnt);     return 0; }

and simpler hello.asm:

extern cnt section .text  global increment  increment:   inc dword [cnt] ret

first main.o typing gcc -c main.c hello.o -- nasm -f macho hello.asm -ddarwin and, finally, executable ld -o main main.o hello.o -arch i386 -lc , error:

ld: warning: -macosx_version_min not specified, assuming 10.10 ld: warning:  ignoring file main.o, file built unsupported file format  (   0xcf 0xfa 0xed 0xfe 0x07 0x00 0x00 0x01 0x03 0x00 0x00 0x00 0x01 0x00 0x00 0x00 ) not architecture being linked (i386): main.o undefined symbols architecture i386:   "_main", referenced from:  implicit entry/start main executable "cnt", referenced from:   increment in hello.o ld: symbol(s) not found architecture i386

how fix linking error?

  • specify architecture (32/64 bit options m32 or m64)
  • link crt files, these files contain runtime - that's code calls main function

modify asm file:

extern _cnt section .text global _increment _increment:   inc dword [_cnt] ret

so final command lines should be: 

gcc -c -m32 main.c nasm -f macho hello.asm -ddarwin ld hello.o main.o /usr/lib/crt1.o  -lc -o main

check arch , execute:

file main main: mach-o executable i386  ./main 1

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