http://binky.org.uk/sources/unportable.c
  http://binky.org.uk/sources/unportable.txt

When I was told that it didn't work any more, I set to work on a new one.
After all, what good is unportable code if it doesn't work?

It had been so long, though. I remember that back then I did it the hard way.
Well, not this time!

First, I nasm'd myself something that worked. In order to be reduced, it can't
use any globals. I used the same trick as before to write stuff, namely push
the data to the stack and use IT as a pointer.

What I came up with was quite simple, and it worked. But that was just
assembler. Now to reduce it.

I wrote a perl script to reduce arbitrary objects to c code:
  http://binky.org.uk/sources/unportable2.pl

So compile:
$ nasm asm.s -f elf && ld -s -o asm asm.o && ./asm

Run the script:
$ ./compile.pl asm.o > casm.c

And compile the result:
$ gcc casm.c -o casm && ./casm
Hello world

Bam. Works. But it was too long, so I went to shave off some bytes. This was
fun:
  http://binky.org.uk/sources/unportable2.s

It's probably as short as it's possible to get. It's shorter than the last one,
anyway.
$ objdump -d asm.o

asm.o:     file format elf32-i386

Disassembly of section .text:

00000000 <_start>:
   0:   31 db                   xor    %ebx,%ebx
   2:   43                      inc    %ebx
   3:   89 d8                   mov    %ebx,%eax
   5:   c1 e0 02                shl    $0x2,%eax
   8:   89 c2                   mov    %eax,%edx
   a:   d1 e2                   shl    %edx
   c:   01 c2                   add    %eax,%edx
   e:   68 72 6c 64 0a          push   $0xa646c72
  13:   68 6f 20 77 6f          push   $0x6f77206f
  18:   68 48 65 6c 6c          push   $0x6c6c6548
  1d:   89 e1                   mov    %esp,%ecx
  1f:   cd 80                   int    $0x80
  21:   93                      xchg   %eax,%ebx
  22:   cd 80                   int    $0x80

With the reduced result:
  http://binky.org.uk/source/unportable2.c