Tips for compiling in 32 bit mode

Tutorials & Resources
1

I recently have been trying to compile some old C programs that were last used in Solarus OS - ie more than 20 years ago. Computers then were 32 bit.

I first tried a 64 bit compile but there were too many problems. Old poorly written C with casts between integers and pointers has issues moving to 64 bit.

So I decided to compile it in 32 bit mode in my 64 bit computer. I worked in Devuan 5.
I have set down here what I discovered are some of the requirements for a 32bit cross compile. Hope it helps someone .

  • use the flag -m32 on the gcc compiler. In a Makefile this is normally set with
    CFLAGS = -m32 or CCFLAGS = -m32
    and it seems to be necessary to also set this flag for the loader
    LDFLAGS = -m32
    to force the loader to look for 32 bit libraries
  • setup the architecture. Normally in a 64 bit machine you get this
$ arch
x86_64

but you need to also declare the i386 architecture. Do this with

sudo dpkg --add-architecture i386

dpkg --print-foreign-architectures
i386

After allowing i386 architecture, you need to do

apt-get update

so that your repo database will be updated to contain all the i386 packages

  • install any required 32 bit libraries and accompanying -dev packages. For example
apt-get install libxaw7:i386
apt-get install libxaw7-dev:i386
  • install the multilib package for gcc ( and fortran if needed)
apt-get install gcc-12-multilib
apt-get install gfortran-12-multilib
  • install the cross compile support
apt-get install gcc-12-multilib-x86-64-linux-gnux32
apt-get install gfortran-12-multilib-x86-64-linux-gnux32
  • If there are any local libraries in the program files, recompile them in 32 bit mode.
  • that’s it try to do make all. If you are lucky it may compile
    without errors.

In my case , sadly, there were many errors. Some of the most common issues were

  • needing to add lines like
    #include <stdlib.h>
    to the C code.
  • not able to find .h files
    Typically you get messages about functions being implicitly defined.
    May need to add an include path such as -I/usr/lib/gcc/x86_64-linux-gnu/12/include to the compiler options
  • not able to find libraries. Need to install more i386 libraries.
  • warnings about casts of pointer to integer of wrong size.

I did eventually get it to compile after 60 attempts.
It runs .
but
it will not open an X11 display window. Some problem calling X_CreateWindow(). That’s my problem.
and
there is some library that it can not find

ERROR: ld.so: object '/usr/lib/x86_64-linux-gnu/libgtk3-nocsd.so.0' from LD_PRELOAD cannot be preloaded (wrong ELF class: ELFCLASS64): ignored.

because it does not exist for i386 architecture. It does not seem to matter.

So the message is
If you want to try a 32 bit cross compile, be prepared.
Set up the system properly first.
I wasted a lot of time with ill-prepared attempts.

3 Likes
2

@nevj
Man!!! You would be right at home with LFS!!!

3 Likes