libkern/kmod/c_start.c

   1 /*
   2  * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * The contents of this file constitute Original Code as defined in and
   7  * are subject to the Apple Public Source License Version 1.1 (the
   8  * "License").  You may not use this file except in compliance with the
   9  * License.  Please obtain a copy of the License at
  10  * http://www.apple.com/publicsource and read it before using this file.
  11  *
  12  * This Original Code and all software distributed under the License are
  13  * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  14  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  15  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  16  * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
  17  * License for the specific language governing rights and limitations
  18  * under the License.
  19  *
  20  * @APPLE_LICENSE_HEADER_END@
  21  */
  22 /*
  23     Subtle combination of files and libraries make up the C++ runtime system for kernel modules.  We are dependant on the KernelModule kmod.make and CreateKModInfo.perl scripts to be exactly instep with both this library module and the libkmod module as well.
  24
  25     If you do any maintenance on any of the following files make sure great care is taken to keep them in Sync.
  26     KernelModule.bproj/kmod.make
  27     KernelModule.bproj/CreateKModInfo.perl
  28     KernelModule.bproj/kmodc++/pure.c
  29     KernelModule.bproj/kmodc++/cplus_start.c
  30     KernelModule.bproj/kmodc++/cplus_start.c
  31     KernelModule.bproj/kmodc/c_start.c
  32     KernelModule.bproj/kmodc/c_stop.c
  33
  34     The trick is that the linkline links all of the developers modules.  If any static constructors are used .constructors_used will be left as an undefined symbol.  This symbol is exported by the cplus_start.c routine which automatically brings in the appropriate C++ _start routine.  However the actual _start symbol is only required by the kmod_info structure that is created and initialized by the CreateKModInfo.perl script.  If no C++ was used the _start will be an undefined symbol that is finally satisfied by the c_start module in the kmod library.
  35
  36     The linkline must look like this.
  37         *.o -lkmodc++ kmod_info.o -lkmod
  38  */
  39 #include <mach/mach_types.h>
  40
  41 // These global symbols will be defined by CreateInfo script's info.c file.
  42 extern kmod_start_func_t *_realmain;
  43
  44 __private_extern__ kern_return_t _start(kmod_info_t *ki, void *data)
  45 {
  46     if (_realmain)
  47         return (*_realmain)(ki, data);
  48     else
  49         return KERN_SUCCESS;
  50 }