Jail.c script for Majesty on Linux

#define _GNU_SOURCE
#include <dlfcn.h>
#include <SDL/SDL.h>

// pointer to the real function
Uint8* (*real_SDL_GetKeyState) (int *numkeys) = NULL;

void __attribute__ ((constructor)) jail_init(void)
{
    // match the library name loaded by our binary target
    dlopen("libSDL-1.2.so.0", RTLD_LAZY);
    real_SDL_GetKeyState = dlsym(RTLD_NEXT, "SDL_GetKeyState");
}

// the wrapper
Uint8* SDL_GetKeyState (int *numkeys)
{
    Uint8* keys;
    SDL_GrabMode mode;

    keys = (*real_SDL_GetKeyState)(numkeys);

    if ((keys[SDLK_LCTRL] && keys[SDLK_SPACE])|| keys[SDLK_RCTRL])
    {
        keys[SDLK_SPACE] = 0;
        mode = SDL_WM_GrabInput(SDL_GRAB_QUERY);
        SDL_WM_GrabInput(mode == SDL_GRAB_OFF ? SDL_GRAB_ON : SDL_GRAB_OFF);
    }

    return keys;
}