Imitate/emulate a big-endian behavior in C? [duplicate]

Question

I was wondering if it's possible to emulate a big-endian behavior, for testing purpose?

via either windows or linux , mingw or gcc. Here's a sample of code which I would like the emulation to return big endian:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include <limits.h>
#if CHAR_BIT != 8
#error "Unsupported char size for detecting endianness"
#endif

int main (void)
{
  short int word = 0x0001;
  char *byte = (char *) &word;
  if (byte[0]) printf("little endian");
  else printf("big endian");
  return 0;
}

Answer 1

You can't switch endianes for testing purposes or anything like that. What you can do is, to install an emulator for a big-endian architecture and compile your program for the emulator. Here's one way, under:

http://people.debian.org/~aurel32/qemu/

are Debian disk images for all kinds of QEMU supported architectures. mips, sparc and arm are big-endian (do not download anything ending with -el). I'm using Debian Lenny for MIPS ( http://people.debian.org/~aurel32/qemu/mips/ ). Install QEMU for your platform, then follow the instructions on the MIPS-page to download a image and kernel file.

Now you can boot into a Debian 5 for MIPS right from your console. Login to you virtual machine, become super user (the password is "root") and install the C-compiler:

debian-mips:~# su -
debian-mips:~# apt-get update
debian-mips:~# apt-get install gcc

fire up an editor and enter your program:

debian-mips:~# pico foo.c
debian-mips:~# gcc foo.c
debian-mips:~# ./a.out
big endian

UPDATE (2021-07-27) Just want to add, for anyone reading this 11 years later, that using the multiarch privileged container in docker is an easier and faster way to get a testing setup. Getting a s390x (big endian) running is as easy as:

$ docker run --rm --privileged multiarch/qemu-user-static --reset -p yes
$ docker run --rm -it s390x/ubuntu bash

Also, this works unter Docker Desktop for Windows.

See https://github.com/multiarch/qemu-user-static for more infos.

Answer 2

I wanted big-endian emulation on my little-endian Intel machine to test a program for byte order related issues. QEMU PowerPC emulator seemed like a good solution. I have documented the steps to set it up below.

1) Installed QEMU.

nifty:~# aptitude update && aptitude install qemu

2) Downloaded Mac-on-Linux from http://sourceforge.net/projects/mac-on-linux/files/ and copied the 'video.x' file in the download to '/usr/share/qemu'. This was necessary to prevent qemu-system-ppc from complaining about it.

nifty:~# tar -xjf mol-0.9.72.1.tar.bz2
nifty:~# cp mol-0.9.72.1/mollib/drivers/video.x /usr/share/qemu

3) Downloaded Debian for PowerPC and installed it on a QEMU hard disk image.

susam@nifty:~/qemu$ wget --no-verbose http://cdimage.debian.org/debian-cd/5.0.4/powerpc/iso-cd/debian-504-powerpc-CD-1.iso
2010-06-19 02:55:06 URL:http://caesar.acc.umu.se/debian-cd/5.0.4/powerpc/iso-cd/debian-504-powerpc-CD-1.iso[675569664/675569664] -> "debian-504-powerpc-CD-1.iso" [1]
susam@nifty:~/qemu$ qemu-img create powerpc.img 2G
Formatting 'powerpc.img', fmt=raw size=2147483648
susam@nifty:~/qemu$ qemu-system-ppc -hda powerpc.img -cdrom debian-504-powerpc-CD-1.iso -boot d -m 512

4) Booted the QEMU PowerPC emulator with the hard disk image.

susam@nifty:~/qemu$ qemu-system-ppc -hda powerpc.img -m 512

5) Verified that I was really on a big endian system by writing a simple C program.

susam@lilliput:~$ cat endian.c
#include <stdio.h>

int main()
{
    int n = 0x1;
    printf(*((char *) &n) ? "little-endian\n" : "big-endian\n");
    return 0;
}
susam@lilliput:~$ gcc endian.c && ./a.out
big-endian
susam@lilliput:~$ 

In case you missed the pun, Lilliputians were originally big-endians.