libkern/kmod/c_start.c

   1 /*
   2  * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * Copyright (c) 1999-2003 Apple Computer, Inc.  All Rights Reserved.
   7  *
   8  * This file contains Original Code and/or Modifications of Original Code
   9  * as defined in and that are subject to the Apple Public Source License
  10  * Version 2.0 (the 'License'). You may not use this file except in
  11  * compliance with the License. Please obtain a copy of the License at
  12  * http://www.opensource.apple.com/apsl/ and read it before using this
  13  * file.
  14  *
  15  * The Original Code and all software distributed under the License are
  16  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  17  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  18  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  19  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  20  * Please see the License for the specific language governing rights and
  21  * limitations under the License.
  22  *
  23  * @APPLE_LICENSE_HEADER_END@
  24  */
  25 /*
  26     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.
  27
  28     If you do any maintenance on any of the following files make sure great care is taken to keep them in Sync.
  29     KernelModule.bproj/kmod.make
  30     KernelModule.bproj/CreateKModInfo.perl
  31     KernelModule.bproj/kmodc++/pure.c
  32     KernelModule.bproj/kmodc++/cplus_start.c
  33     KernelModule.bproj/kmodc++/cplus_start.c
  34     KernelModule.bproj/kmodc/c_start.c
  35     KernelModule.bproj/kmodc/c_stop.c
  36
  37     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.
  38
  39     The linkline must look like this.
  40         *.o -lkmodc++ kmod_info.o -lkmod
  41  */
  42 #include <mach/mach_types.h>
  43
  44 // These global symbols will be defined by CreateInfo script's info.c file.
  45 extern kmod_start_func_t *_realmain;
  46
  47 __private_extern__ kern_return_t _start(kmod_info_t *ki, void *data)
  48 {
  49     if (_realmain)
  50         return (*_realmain)(ki, data);
  51     else
  52         return KERN_SUCCESS;
  53 }