Error when trying to run .asm file on NASM on Ubuntu

Question

I'm using ubuntu 64-bit and trying to run a .asm file on NASM. But it returns this error when I try to run the following code. What Iḿ trying to do is build an executable by compiling (or assembling) object file from the source $ nasm -f elf hello.asm, and then after created the file hello.o is producing executable file itself from the object file by invoking linker

$ ld -s -o hello hello.o 

This will finally build hello executable.

I'm following this tutorial http://www.faqs.org/docs/Linux-HOWTO/Assembly-HOWTO.html

Error:

i386 architecture of input file `hello.o' is incompatible with i386:x86-64 output

Code:

     section .data              ;section declaration   msg     db      "Hello, world!",0xa    ;our dear string  len     equ     $ - msg                 ;length of our dear string   section .text              ;section declaration               ;we must export the entry point to the ELF linker or      global _start       ;loader. They conventionally recognize _start as their              ;entry point. Use ld -e foo to override the default.   _start:   ;write our string to stdout           mov     edx,len ;third argument: message length          mov     ecx,msg ;second argument: pointer to message to write          mov     ebx,1   ;first argument: file handle (stdout)          mov     eax,4   ;system call number (sys_write)          int     0x80   ;call kernel    ;and exit       mov    ebx,0   ;first syscall argument: exit code          mov     eax,1   ;system call number (sys_exit)          int     0x80   ;call kernel 

Answer 1

This looks like it may be a simple mismatch between what's produced by nasm and what ld is trying to make:

i386 architecture of input file 'hello.o' is incompatible with i386:x86-64 output 

In other words, nasm has produced a 32-bit object file hello.o and ld wants to take that and make a 64-bit executable file.

The nasm -hf command should give you the available output formats:

valid output formats for -f are (`*' denotes default):   * bin       flat-form binary files (e.g. DOS .COM, .SYS)     ith       Intel hex     srec      Motorola S-records     aout      Linux a.out object files     aoutb     NetBSD/FreeBSD a.out object files     coff      COFF (i386) object files (e.g. DJGPP for DOS)     elf32     ELF32 (i386) object files (e.g. Linux)     elf       ELF (short name for ELF32)      elf64     ELF64 (x86_64) object files (e.g. Linux)     as86      Linux as86 (bin86 version 0.3) object files     obj       MS-DOS 16-bit/32-bit OMF object files     win32     Microsoft Win32 (i386) object files     win64     Microsoft Win64 (x86-64) object files     rdf       Relocatable Dynamic Object File Format v2.0     ieee      IEEE-695 (LADsoft variant) object file format     macho32   NeXTstep/OpenStep/Rhapsody/Darwin/MacOS X (i386) object files     macho     MACHO (short name for MACHO32)     macho64   NeXTstep/OpenStep/Rhapsody/Darwin/MacOS X (x86_64) object files     dbg       Trace of all info passed to output stage 

I see that your linked tutorial asks you to run:

nasm -f elf hello.asm 

Try using:

nasm -f elf64 hello.asm 

instead, and you may find ld stops complaining about the input file.

Answer 2

You need to tell the linker to produce an i386 output file, since you're writing i386 assembly:

ld -m elf_i386 -s -o hello hello.o