How to create 4KB Linux binaries that render a 3D scene?

The main reason why with the standard settings you can't make a small tool is that a lot of symbols and references to standard libraries are pulled into your binary. You must be explicit to to remove even that basic stuff.

Here's how I did it:

http://phresnel.org/gpl/4k/ntropy2k7/

Relevant Options:

Mostly self-explaining:

gcc main.c -o fourk0001 -Os -mfpmath=387 \  -mfancy-math-387 -fmerge-all-constants -fsingle-precision-constant \  -fno-math-errno -Wall -ldl -ffast-math -nostartfiles -nostdlib  \  -fno-unroll-loops -fshort-double

Massage:

strip helps you get rid of unneeded symbols embedded in your binary:

strip -R .note -R .comment -R .eh_frame -R .eh_frame_hdr -s fourk0001

Code:

You may have to tweak and trial and error a lot. Sometimes, a loop gives smaller code, sometimes a call, sometimes a force inlined function. In my code, e.g., instead of having a clean linked list that contains all flame transforms in fancy polymorphic style, I have a fixed array where each element is a big entity containing all parameters, used or unused, as a union of all flames as per Scott Draves flame paper.

Your tricks won't be portable, other versions of g++ might give suboptimal results.

Note that with above parameters, you do not write a main() function, but rather a _start() function.

Also note that using libraries is a bit different. Instead of linking SDL and standard library functions the classy, convenient way, you must do it manually. E.g.

void *libSDL = dlopen( "libSDL.so", RTLD_LAZY );void *libC = dlopen( "libc.so", RTLD_LAZY );#if 1    SDL_SetVideoMode_t sym_SDL_SetVideoMode = dlsym(libSDL, "SDL_SetVideoMode");    g_sdlbuff = sym_SDL_SetVideoMode(WIDTH,HEIGHT,32,SDL_HWSURFACE|SDL_DOUBLEBUF);#else    ((SDL_SetVideoMode_t)dlsym(libSDL, "SDL_SetVideoMode"))(WIDTH,HEIGHT,32,SDL_HWSURFACE|SDL_DOUBLEBUF);#endif//> need malloc, probably kinda craft (we only use it once :| )//> load some sdl cruft (cruft!)malloc_t sym_malloc = dlsym( libC, "malloc" );sym_rand   = dlsym( libC, "rand" );sym_srand  = dlsym( libC, "srand" );sym_SDL_Flip          = dlsym(libSDL, "SDL_Flip");sym_SDL_LockSurface   = dlsym(libSDL, "SDL_LockSurface");sym_SDL_UnlockSurface = dlsym(libSDL, "SDL_UnlockSurface");sym_SDL_MapRGB        = dlsym(libSDL, "SDL_MapRGB");

And even though no assembler has to be harmed, your code might yield UB.

edit:

Oops, I lied about assembly.

void _start() {    ...    asm( "int $0x80" :: "a"(1), "b"(42) );}

this will make your program return 42.

A Whirlwind Tutorial on Creating Really Teensy ELF Executables for Linux is an interesting article that goes through a step-by-step process to create an ELF executable as small as possible.

I don't want to spoil the ending, but the author gets it down to a lot smaller than 4K ;)

Take a look at this article in KSplice blog from a while back. It talks about linking without the standard libraries.

https://blogs.oracle.com/ksplice/entry/hello_from_a_libc_free