nasm cannot generate ELF binaries directly, only .o files which must be formally linked. So you have to use `ld` on the generated object file(s) to produce a bi

nasm cannot generate ELF binaries directly, only .o files which must be formally linked. So you have to use `ld` on the generated object file(s) to produce a binary. (I've not (yet) tested using LLVM's new linker or the linker stages from other compilers.) Some extremely anecdotal and unscientific testing I did a little while back seemed to show that fasm's "hello world" example is several scales smaller than nasm's. I decided to be scientific and re-do my test with similar programs. fasm includes a hello-world program in the distribution: format ELF64 executable 3 segment readable executable entry $ mov edx, len lea rsi, [msg] mov edi, 1 mov eax, 1 syscall xor edi, edi mov eax, 60 syscall segment readable writeable msg db 'Hello world!', 10 len = $ - msg Here I pretty much converted the fasm example to match nasm as closely as possible (using various online references to get an idea of how it should look for nasm): section .text global _start _start: mov edx, len mov rsi, msg mov eax, 1 mov edi, 1 syscall xor edi, edi mov eax, 60 syscall section .data msg db "hello, world!", 10 len equ $ - msg What isn't really possible with nasm is to remove the symbol table and _start export. This makes a phenomenal difference in file size. Here's nasm: $ ls -lh nasm64 nasm64.o -rwxr-xr-x 1 i336 users 512 Oct 9 10:10 nasm64 -rw-r--r-- 1 i336 users 880 Oct 9 10:10 nasm64.o Because fasm doesn't need to mess around with exports or symbols and can just write binaries directly, it absolutely kills nasm: $ ls -lh hello64 -rwxr-xr-x 1 i336 users 222 Oct 9 10:29 hello64 One of my major interests in assembly language is in having tight control over output file size, so fasm is super interesting to me. I am very curious as to the file format differences though. Apparently nasm generates SYSV-format ELF files, while fasm generates a Linux-specific variant...? $ file nasm64 nasm64: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), statically linked, stripped $ file hello64 hello64: ELF 64-bit LSB executable, x86-64, version 1 (GNU/Linux), statically linked, stripped That's interesting. I'm genuinely curious what this means. As far as the size differences are concerned, http://www.muppetlabs.com/~breadbox/software/tiny/teensy.html http://www.muppetlabs.com/~breadbox/software/tiny/teensy.htm... shows that to make smaller stuff than ld generates, you have to start hand-composing the ELF file. So fasm is pretty much the only way to produce the smallest ELFs with minimal fuss on Linux.