How to compile a 32-bit binary on a 64-bit linux machine with gcc/cmake

Question

Is it possible to compile a project in 32-bit with cmake and gcc on a 64-bit system? It probably is, but how do I do it?

When I tried it the "ignorant" way, without setting any parameters/flags/etc, just setting LD_LIBRARY_PATH to find the linked libraries in ~/tools/lib it seems to ignore it and only look in subdirectories named lib64.

A push in the right direction would be great. Thanks!

Answer 1

export CFLAGS=-m32

Answer 2

One way is to setup a chroot environment. Debian has a number of tools for that, for example debootstrap

Answer 3

$ gcc test.c -o testc
$ file testc
testc: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.9, not stripped
$ ldd testc 
    linux-vdso.so.1 =>  (0x00007fff227ff000)
    libc.so.6 => /lib64/libc.so.6 (0x000000391f000000)
    /lib64/ld-linux-x86-64.so.2 (0x000000391ec00000)
$ gcc -m32 test.c -o testc
$ file testc
testc: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.9, not stripped
$ ldd testc
    linux-gate.so.1 =>  (0x009aa000)
    libc.so.6 => /lib/libc.so.6 (0x00780000)
    /lib/ld-linux.so.2 (0x0075b000)

In short: use the -m32 flag to compile a 32-bit binary.

Also, make sure that you have the 32-bit versions of all required libraries installed (in my case all I needed on Fedora was glibc-devel.i386)

Answer 4

In later versions of CMake, one way to do it on each target is:

set_target_properties(MyTarget PROPERTIES COMPILE_FLAGS "-m32" LINK_FLAGS "-m32")

I don't know of a way to do it globally.