x86-assembly-cheat/getting-started.md

Getting started

Ubuntu 14.04 quick start

sudo apt-get install build-essential gcc-multilib nasm

# Run all programs in the current directory.
make test

# Run cmp.asm.
make run RUN=cmp

# Run a default program, usually a main file or a hello world.
make run

Pre-requisites

• an x86 processor or emulator, 32 or 64-bit. We provide a Vagrantfile.

  Beware that the virtual machine provided by Vagrantfile may have less features than your own CPU. Check cat /proc/cpuinfo inside the VM.

• common GNU/Linux build tools: make, gcc, nasm, Binutils (as, ld).

• OS: most programs should work on any OS, including Linux, Windows and Mac, because we use the C standard library libc instead of direct system calls for IO via lib/.

  However, I have only tested them on Ubuntu, which likely means that you will need to do a little bit of work to get them working elsewhere.

  If you do to get the examples working on another OS, please send a patch documenting the installation and patching whatever was needed.

  Porting will likely mean:

  • installing the required assemblers / compilers
  • getting make or rewriting our trivial build script into something more portable like Python
  • possibly messing around with a few calling conventions to the stdlib

  Architecture and OS specifics are clearly separated in sub-directories. E.g., Linux-only programs will be put into the linux directory.

Assertions

One distinctive feature of this tutorial is that we have assertions.

So edit a test to make it fail and see it blow up. E.g., modify add.asm to contain:

mov eax, 0
add eax, 1
ASSERT_EQ 2

and run:

make test

It will now say that a test failed, because usually:

0 + 1 != 2

64-bit CPUs can run this

x86-64 is a backwards compatible extension of IA-32, and has a mode which emulates IA-32.

x86-64 Linux is able to run IA-32 code out of the box using the hardware backwards compatibility if compiled with CONFIG_IA32_EMULATION=y, which is the default in any sane distro.

You only have to make sure that gcc -m32 hello_world.c compiles correctly.

The hard part is ensuring that the linker is able to find the 32-bit version of the glibc used by the driver: any GCC installation can do the compilation correctly. On Ubuntu, all you need to do is:

sudo apt-get install gcc-multilib

See also:

• http://stackoverflow.com/questions/22355436/how-to-compile-32-bit-apps-on-64-bit-ubuntu
• http://stackoverflow.com/questions/9807581/cannot-find-crtn-o-linking-32-bit-code-on-64-bit-system

If you don't have a compatible CPU, use the Vagrantfiles provided in each directory or your favorite virtualization method.