I’ve been writing a lot of articles recently about compiling C and assembly programs on my 64-bit machine. But eventually I needed to compile a 32-bit program and I thought I would explain how I did that in case anyone else runs into trouble.

Using the -m32 flag

To compile a 32-bit program with gcc you can just use the m32 flag (which you’ll find under i386 and x86-64 Options on the gcc man page). But if you’re on a 64-bit machine, don’t be surprised if you see something like this:

# gcc -m32 -o example32bit example32bit.c
In file included from /usr/include/features.h:378,
                 from /usr/include/stdio.h:28,
                 from example32bit.c:1:
/usr/include/gnu/stubs.h:7:27: error: gnu/stubs-32.h: No such file or directory

Installing the 32-bit glibc headers

You see that because you don’t have the 32-bit glibc headers installed. That’s not a problem though, since most package managers should have them available for installation. If you’re on a Debian or Ubuntu machine you can install them like this:

# apt-get install gcc-multilib

Look ma, no compiler errors!

# gcc -m32 -o example32bit example32bit.c
#

Tada!