/** @file
 * IPRT - Runtime Loader Generation.
 */

/*
 * Copyright (C) 2008-2015 Oracle Corporation
 *
 * This file is part of VirtualBox Open Source Edition (OSE), as
 * available from http://www.virtualbox.org. This file is free software;
 * you can redistribute it and/or modify it under the terms of the GNU
 * General Public License (GPL) as published by the Free Software
 * Foundation, in version 2 as it comes in the "COPYING" file of the
 * VirtualBox OSE distribution. VirtualBox OSE is distributed in the
 * hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
 *
 * The contents of this file may alternatively be used under the terms
 * of the Common Development and Distribution License Version 1.0
 * (CDDL) only, as it comes in the "COPYING.CDDL" file of the
 * VirtualBox OSE distribution, in which case the provisions of the
 * CDDL are applicable instead of those of the GPL.
 *
 * You may elect to license modified versions of this file under the
 * terms and conditions of either the GPL or the CDDL or both.
 */

#include <iprt/types.h>
#ifdef RT_RUNTIME_LOADER_GENERATE_BODY_STUBS
# include <iprt/ldr.h>
# include <iprt/log.h>
# include <iprt/once.h>
#endif

/** @defgroup grp_rt_runtime_loader     Runtime Loader Generation
 * @ingroup grp_rt
 *
 * How to use this loader generator
 *
 * This loader generator can be used to generate stub code for loading a shared
 * library and its functions at runtime, or for generating a header file with
 * the declaration of the loader function and optionally declarations for the
 * functions loaded.  It should be included in a header file or a C source
 * file, after defining certain macros which it makes use of.
 *
 * To generate the C source code for function proxy stubs and the library
 * loader function, you should define the following macros in your source file
 * before including this header:
 *
 *  RT_RUNTIME_LOADER_LIB_NAME       - the file name of the library to load
 *  RT_RUNTIME_LOADER_FUNCTION       - the name of the loader function
 *  RT_RUNTIME_LOADER_INSERT_SYMBOLS - a macro containing the names of the
 *                                     functions to be loaded, defined in the
 *                                     following pattern:
 * @code
 * #define RT_RUNTIME_LOADER_INSERT_SYMBOLS \
 *  RT_PROXY_STUB(func_name, ret_type, (long_param_list), (short_param_list)) \
 *  RT_PROXY_STUB(func_name2, ret_type2, (long_param_list2), (short_param_list2)) \
 *  ...
 * @endcode
 *
 * where long_param_list is a parameter list for declaring the function of the
 * form (type1 arg1, type2 arg2, ...) and short_param_list for calling it, of
 * the form (arg1, arg2, ...).
 *
 * To generate the header file, you should define RT_RUNTIME_LOADER_FUNCTION
 * and if you wish to generate declarations for the functions you should
 * additionally define RT_RUNTIME_LOADER_INSERT_SYMBOLS as above and
 * RT_RUNTIME_LOADER_GENERATE_DECLS (without a value) before including this
 * file.
 *
 * @{
 */
/** @todo this is far too complicated.  A script for generating the files would
 * probably be preferable.
 *
 * bird> An alternative is to generate assembly jump wrappers, this only
 * requires the symbol names and prefix.  I've done this ages ago when we forked
 * the EMX/GCC toolchain on OS/2...  It's a wee bit more annoying in x86 PIC/PIE
 * mode, but nothing that cannot be dealt with.
 */
/** @todo r=bird: The use of RTR3DECL here is an unresolved issue. */
/** @todo r=bird: The lack of RT_C_DECLS_BEGIN/END is an unresolved issue.  Here
 *        we'll get into trouble if we use the same symbol names as the
 *        original! */
/** @todo r=bird: The prefix usage here is very confused: RT_RUNTIME_LOADER_XXX,
 *        RT_PROXY_STUB, etc. */

#ifdef RT_RUNTIME_LOADER_GENERATE_BODY_STUBS

/* The following are the symbols which we need from the library. */
# define RT_PROXY_STUB(function, rettype, signature, shortsig) \
    void (*function ## _fn)(void); \
    RTR3DECL(rettype) function signature \
    { return ( (rettype (*) signature) function ## _fn ) shortsig; }

RT_RUNTIME_LOADER_INSERT_SYMBOLS

# undef RT_PROXY_STUB

/* Now comes a table of functions to be loaded from the library. */
typedef struct
{
    const char *pszName;
    void (**ppfn)(void);
} RTLDRSHAREDFUNC;

# define RT_PROXY_STUB(s, dummy1, dummy2, dummy3 ) { #s , & s ## _fn } ,
static RTLDRSHAREDFUNC g_aSharedFuncs[] =
{
    RT_RUNTIME_LOADER_INSERT_SYMBOLS
    { NULL, NULL }
};
# undef RT_PROXY_STUB

/**
 * The function which does the actual work for RT_RUNTIME_LOADER_FUNCTION,
 * serialised for thread safety.
 */
static DECLCALLBACK(int) rtldrLoadOnce(void *)
{
    RTLDRMOD    hLib;
    int         rc;

    LogFlowFunc(("\n"));
    rc = RTLdrLoad(RT_RUNTIME_LOADER_LIB_NAME, &hLib);
    for (unsigned i = 0; RT_SUCCESS(rc) && g_aSharedFuncs[i].pszName != NULL; ++i)
        rc = RTLdrGetSymbol(hLib, g_aSharedFuncs[i].pszName, (void **)g_aSharedFuncs[i].ppfn);
    LogFlowFunc(("rc = %Rrc\n", rc));

    return rc;
}

/**
 * Load the shared library RT_RUNTIME_LOADER_LIB_NAME and resolve the symbols
 * pointed to by RT_RUNTIME_LOADER_INSERT_SYMBOLS.
 *
 * May safely be called from multiple threads and will not return until the
 * library is loaded or has failed to load.
 *
 * @returns IPRT status code.
 */
RTR3DECL(int) RT_RUNTIME_LOADER_FUNCTION(void)
{
    static RTONCE   s_Once = RTONCE_INITIALIZER;
    int             rc;

    LogFlowFunc(("\n"));
    rc = RTOnce(&s_Once, rtldrLoadOnce, NULL);
    LogFlowFunc(("rc = %Rrc\n", rc));

    return rc;
}

#elif defined(RT_RUNTIME_LOADER_GENERATE_HEADER)
# ifdef RT_RUNTIME_LOADER_GENERATE_DECLS
/* Declarations of the functions that we need from
 * RT_RUNTIME_LOADER_LIB_NAME */
#  define RT_PROXY_STUB(function, rettype, signature, shortsig) \
    RTR3DECL(rettype) ( function ) signature ;

RT_RUNTIME_LOADER_INSERT_SYMBOLS

#  undef RT_PROXY_STUB
# endif /* RT_RUNTIME_LOADER_GENERATE_DECLS */

/**
 * Try to dynamically load the library.  This function should be called before
 * attempting to use any of the library functions.  It is safe to call this
 * function multiple times.
 *
 * @returns iprt status code
 */
RTR3DECL(int) RT_RUNTIME_LOADER_FUNCTION(void);

#else
# error "One of RT_RUNTIME_LOADER_GENERATE_HEADER or RT_RUNTIME_LOADER_GENERATE_BODY_STUBS must be defined when including this file"
#endif

/** @} */

