libsa/lastkerneldataconst.c

   1 /*
   2  * Copyright (c) 2014 Apple Inc. All rights reserved.
   3  *
   4  * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. The rights granted to you under the License
  10  * may not be used to create, or enable the creation or redistribution of,
  11  * unlawful or unlicensed copies of an Apple operating system, or to
  12  * circumvent, violate, or enable the circumvention or violation of, any
  13  * terms of an Apple operating system software license agreement.
  14  *
  15  * Please obtain a copy of the License at
  16  * http://www.opensource.apple.com/apsl/ and read it before using this file.
  17  *
  18  * The Original Code and all software distributed under the License are
  19  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  20  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  21  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  22  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  23  * Please see the License for the specific language governing rights and
  24  * limitations under the License.
  25  *
  26  * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
  27  */
  28
  29 #include <mach/vm_param.h>
  30
  31 /*
  32  * This file is compiled and linked to be the last .o of the __const section
  33  * of the __DATA segment (see MakeInc.kernel, lastkernelconstructor is placed
  34  * in the __LAST segment.)
  35  *
  36  * This blank page allows us to safely map the const section RO while the rest
  37  * of __DATA is RW. This is needed since ld has no way of specifying section size
  38  * alignment and no straight forward way to specify section ordering.
  39  */
  40
  41 #if defined(__arm64__)
  42 /* PAGE_SIZE on ARM64 is an expression derived from a non-const global variable */
  43 #define PAD_SIZE        PAGE_MAX_SIZE
  44 #else
  45 #define PAD_SIZE        PAGE_SIZE
  46 #endif
  47
  48 static const uint8_t __attribute__((section("__DATA,__const"))) data_const_padding[PAD_SIZE] = {[0 ... PAD_SIZE - 1] = 0xFF};
  49 const vm_offset_t    __attribute__((section("__DATA,__data")))  _lastkerneldataconst         = (vm_offset_t)&data_const_padding[0];
  50 const vm_size_t      __attribute__((section("__DATA,__data")))  _lastkerneldataconst_padsize = sizeof(data_const_padding);