Is it possible to run x86 assembly on a x64 operating system?

Question

Recently I decided that it was worth getting a try on basic x86 assembly so that it would be easier to debug programs, etc, etc. So I started (about a week ago) learning x86 ass

Answer 1

Linux explicitly implements 32 bit support if the compilation option:

CONFIG_IA32_EMULATION=y

is set.

This is done by most sane distros, including Ubuntu 14.04.

32-bit emulation is of course only possible because x86-64 processors are designed to be backwards compatible with 32-bit executables via a 32-bit emulation mode which the kernel knows how to use.

Another thing you have to worry about is the libraries: to compile 32-bit programs, you need 32-bit libraries. On Ubuntu 14.04 AMD64:

sudo apt-get install gcc-multilib

Then we can easily test it out with a hello world:

#include 
#include 

int main() {
    puts("hello world");
    return EXIT_SUCCESS;
}

and:

gcc -m32 hello_world.c
./a.out

Which prints:

hello world

And:

file a.out

confirms that it is 32 bit:

ELF 32-bit LSB  executable, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.24, BuildID[sha1]=358f7969deeb2f24a8dd932a0d296887af4eae30, not stripped