/*
 * Helper header for LD_PRELOAD related headers macros. Must be loaded _first_
 * (for RTLD_NEXT)!
 *
 * Copyright (C) 2012-2013  Simon Ruderich
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#ifndef LDPRELOAD_H
#define LDPRELOAD_H 1

/* Necessary for RTLD_NEXT. */
#define _GNU_SOURCE

/* abort() */
#include <stdlib.h>
/* dlsym() */
#include <dlfcn.h>
#include <errno.h>

static void *dlsym_function(char const *name) noinline;
/* Load the function name using dlsym() and return it. Terminate program on
 * failure. Split in function and macro to reduce code inserted into the
 * function using the macro. */
static void *dlsym_function(char const *name) {
    void *result;

    int saved_errno = errno; /* just in case */

    /* Clear possibly existing error. */
    dlerror();
    result = dlsym(RTLD_NEXT, name);
    /* Not much we can do. Most likely the other output functions failed to
     * load too. */
    if (dlerror() != NULL) {
        abort();
    }

    errno = saved_errno;
    return result;
}

#define DLSYM_FUNCTION(pointer, name) \
    if (unlikely(!(pointer))) { \
        *(void **) (&(pointer)) = dlsym_function(name); \
    }

#endif