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I know very little Assembly Language, but what I recall is that you can skip the libc dependency on Linux if you just run the system call yourself.

So the tiny snippet at the top will become, for instance:

    .text
    .globl _main
    _main:
      subq $8, %rsp
      movq $0, %rdi
      movq $1, %rax
      movq $2, %rbx
      int $0x80
The last three lines choose the 'exit' system call¹, load the number 2 to be its argument, and make the call. Then you can get an executable like so:

    as nothing.s -o nothing.o

    ld nothing.o -o nothing -e _main
Then you can run it and check the return value.

¹ http://docs.cs.up.ac.za/programming/asm/derick_tut/syscalls....



I would advise against interrupt-based syscalls in for x86 platforms in linux... a lot of optimization work has been done for x86-32 via vDSO (and, afaik, x86-64 interrupt-based syscalls are just there for compatibility reasons, but I've been wrong before)

For linux x86-64 syscalls, proper way is to use "syscall" instruction. For linux x86-32 stuff, best way is to make a call via vDSO with "call $gs:0x10" (hopefully i didn't butcher AT&T syntax) so the kernel can dictate (via the vDSO) the best way to actually get you to the point of performing the syscall.

and, to your point, I recommend that anyone disassemble their code compiled with libc (and look at the differences between linux, os x, bsd, whatever)... it gets really interesting how much is added and how each OS handles it.


Awesome! Thank you for your advice.

Either way, I am proceeding with the rest by using what someone else recommended I do, which is use `gcc -nostartfiles`. Looking at gcc in verbose mode reveals an ld command line I could use to run his code without modification:

    ld nothing.o -o nothing -e _main -dynamic-linker /lib64/ld-linux-x86-64.so.2 -lc
For some reason, `/lib/ld64.so.2` is not linked to `/lib64/ld-linux-x86-64.so.2` even though `ld` on Linux seems to look there by default (and fails because none of the mainstream distributions make that link).




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