Smallest x86 ELF Hello World

by shawndumas • 15 years ago

89 36 15 years ago

pgbovine• 15 years ago

a cool project would be to make a webapp that implements the following contest: create an ELF binary to do X with the smallest number of bytes.

DanBC• 15 years ago

...why not just use the Stack Exchange "Code Golf" website?

(http://codegolf.stackexchange.com/)

adestefan• 15 years ago

Is this the next "how fast is Fibonacci" fiasco?

drv2• 15 years ago

The classic resource for this (does the same sort of tricks, taken to an extreme: code overlaid with tables, tables overlaid with other tables, etc.):

http://www.muppetlabs.com/~breadbox/software/tiny/

(62-byte hello world among other things)

linhat2• 15 years ago

how about 45 bytes...

http://www.muppetlabs.com/~breadbox/software/tiny/teensy.htm...

drv2• 15 years ago

Indeed, except that one doesn't print "Hello world". :)

iseyler• 15 years ago

How about 31 bytes?

http://www.returninfinity.com/baremetal-helloworld.html

Why use ELF or Linux? Flat binaries (and a custom OS) to the rescue! :)

breadbox• 15 years ago

Many years ago I used to have a 58-byte version, but around the time that x86-64 was being developed, Linux started examining (and thus validating) a couple more fields in the ELF header. It's really a shame, because the corner-cutting in the 62-byte version isn't nearly as impressive (in my own opinion).

garethsprice2• 15 years ago

$ echo "Hello World" > hw.php && php hw.php Hello World $ ls -l hw.php -rw-r--r-- 1 gareth staff 12 Oct 11 11:23 hw.php

By this stupid metric, PHP is the greatest programming language ever made.

12 byte Hello World must mean that it's also the ideal solution for every other programming problem, right?

delinka• 15 years ago

Your implementation is not x86 ELF. Regardless, I don't recall the author's insistence that finding the smallest executable was desirable. "Stupid metrics" make for great educational exercises.

maratd2• 15 years ago

First, PHP is the greatest programming language ever made. (imagine DiCaprio screaming "I'm the king of the world!" on the Titanic)

Second, there is no point in using it for that when you have bash ... because bash has echo built-in and bash is a programming language:

$ echo "Hello World!"

1 line bitches! I can feel my unix beard growing ...

ez77• 15 years ago

Unless you set +H in bash, including a '!' insisde double quotes is a bad idea.

yan• 15 years ago

I believe you entirely missed the point. This was more of an "Look at how you can abuse the loader and play with ELF headers" and in general show an interesting 'hacky' article, not "this is smaller, thus more efficient" argument.

garethsprice2• 15 years ago

I figured this was posted as a related article to the Dash "Hello World" issue where people are pointing at 17,000 lines of Hello World code, because it includes the runtime when compiled to Javascript.

There was another comment about how this will be the next "Fibonacci debacle", related to how Ted Dzubia trolled the node.js crowd by pointing out it's weakness for CPU-intensive tasks, then had a ton of people wasting time on writing faster Fibonacci algorithms in node just to prove him wrong.

My point was that comparing languages by the size of their Hello World programs is a useless exercise.

moomin• 15 years ago

I think you need to include the size of the php executable...

sambeau3• 15 years ago

Other than as an interesting intellectual exercise is there any reason to do this on a modern computer with Virtual memory?

Surely, once you get below page-size (e.g. 4K) you are just wasting memory that will get loaded anyway?

Moschops• 15 years ago

Practice and understanding for when you've got to work on something that comes with 4k of RAM in total, if you're lucky.

sambeau3• 15 years ago

I edited out the words "apart from on an embedded device with a tiny memory" as I had hoped that the mention of the modern computer and virtual memory would suffice.

But this was a genuine question rather than a put-down. I was hoping to have my assumption debunked.

EDIT: I have no idea why you're being down-voted seems unfair

DanielRibeiro• 15 years ago

Well, on one of the Dart threads, bashing its hello world size, this[1] came up:

Compile "Hello world" into an executable, and see how many kilobytes it takes on most architectures, despite the object file being a few bytes.

This thread pretty much responds to that. It is no 17000 lines, nor 17000K, it is just 142 bytes (other comments suggest it is 62).

[1] http://news.ycombinator.com/item?id=3098660

sambeau3• 15 years ago

It makes more sense for VM byte-code as the bytes not only have to be loaded (probably by the page, again) but the bytes have to be run and possibly jitted, too.

castorpilot• 15 years ago

can get a few bits off by using some well known shellcode techniques. I think xor ebx,ebx is smaller than mov ebx,0, for instance.

VeXocide• 15 years ago

You are right in that

    31 c0             xor %eax, %eax

is shorter than

    b8 00 00 00 00    mov $0, %eax

but that's not the main reason it's often used in shellcode. The xor reg, reg is preferred because it means the resulting shellcode will not contain a null byte. This is desirable since the null-byte is often used as a string terminator, in environment variables for example.

limmeau• 15 years ago

Another reason to use xor: in the old days, ALU reg-reg commands were generally faster than reg-mem moves.

The 8086 assembly tutorial book I used then recommended to use "sub ax, ax" instead because it was less surprising.

jjguy• 15 years ago

same for win32 PEs: http://www.phreedom.org/solar/code/tinype/

surki• 15 years ago

Doing it in C with mixed assembly

  [surki@linux-vrse tt]$ cat | gcc -nostdlib -x c - -o helloworld
  #define SYS_exit  1
  #define SYS_write 4
  #define stdout    1
  
  int strlen(const char *str)
  {
    long len = 0;
    while (str && *str++)
    {
        len++;
    }
  
    return len;
  }
  
  
  void print(const char *str) 
  {
      int len = strlen(str);
  
      long ret;
  
      /* Can't touch ebx directly, PIC uses it */
      __asm__ __volatile__ ("pushl %%ebx\n"
                            "movl  %%esi, %%ebx\n"
                            "int   $0x80\n;"
                            "popl  %%ebx"
                            
                            "a" (SYS_write),
                              "S" ((long) stdout),
                              "c" ((long) str),
                              "d" ((long) len));
      return;
  }
  
  void _start()
  {
    main();
  
    __asm__ __volatile__ (
         "xorl %%ebx, %%ebx\n"
         "int $0x80\n"
         
         "a" (SYS_exit));
  }
  
  int main()
  {
    print("Hello World\n");
    return 0;
  }

  [surki@linux-vrse tt]$ strip -R .comment -R .comment.SUSE.OPTs -R .note.gnu.build-id helloworld
  [surki@linux-vrse tt]$ ll helloworld 
  -rwxr-xr-x 1 suresh users 540 2010-07-21 13:19 helloworld
  
  [surki@linux-vrse tt]$ ./helloworld 
  Hello World

waffenklang• 15 years ago

Very impressive.

joelthelion4• 15 years ago

I wonder if this could be improved with genetic algorithms or similar. The code is pretty small, but the seach space is still pretty huge.

ars2• 15 years ago

Did you post in the wrong thread?

joelthelion4• 15 years ago

Nope. Why couldn't you use a generic optimizer to optimize a piece of code?

Smallest x86 ELF Hello World

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