Ubuntu 16.04
sudo apt-get install gcc-multilib
For some reason, on Ubuntu 17.04, I also needed to install the version specific one:
sudo apt-get install gcc-6-multilib
Then a minimal hello world:
main.c
#include <stdio.h>
int main(void) {
puts("hello world");
return 0;
}
compiles without warning with:
gcc -m32 -ggdb3 -O0 -pedantic-errors -std=c89
-Wall -Wextra -pedantic -o main.out main.c
And
./main.out
outputs:
hello world
And:
file main.out
says:
main.out: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.24, BuildID[sha1]=87c87a83878ce7e7d23b6236e4286bf1daf59033, not stripped
and:
qemu-i386 main.out
also gives:
hello world
but fails on an x86_64 executable with:
./main.out: Invalid ELF image for this architecture
Furthermore, I have:
So I think it works :-)
See also: Cannot find crtn.o, linking 32 bit code on 64 bit system
It is a shame that this package conflicts with the cross compilers like gcc-arm-linux-gnueabihf https://bugs.launchpad.net/ubuntu/+source/gcc-defaults/+bug/1300211
Running versions of the question:
We are able to run 32-bit programs directly on 64-bit Ubuntu because the Ubuntu kernel is configured with:
CONFIG_IA32_EMULATION=y
according to:
grep CONFIG_IA32_EMULATION "/boot/config-$(uname -r)"
whose help on the kernel source tree reads:
Include code to run legacy 32-bit programs under a
64-bit kernel. You should likely turn this on, unless you're
100% sure that you don't have any 32-bit programs left.
This is in turn possible because x86 64 bit CPUs have a mode to run 32-bit programs that the Linux kernel uses.
TODO: what options does gcc-multilib get compiled differently than gcc?
