lib/sdk/crt/except/i386/chkstk_asm.s

   1 /* $Id$
   2  *
   3  * COPYRIGHT:         See COPYING in the top level directory
   4  * PROJECT:           ReactOS kernel
   5  * PURPOSE:           Stack checker
   6  * FILE:              lib/ntdll/rtl/i386/chkstk.s
   7  * PROGRAMER:         KJK::Hyperion <noog@libero.it>
   8  */
   9
  10 #include <reactos/asm.h>
  11 #include <ndk/asm.h>
  12 #define PAGE_SIZE 4096
  13
  14 PUBLIC __chkstk
  15 PUBLIC __alloca_probe
  16 .code
  17
  18 /*
  19  _chkstk() is called by all stack allocations of more than 4 KB. It grows the
  20  stack in areas of 4 KB each, trying to access each area. This ensures that the
  21  guard page for the stack is hit, and the stack growing triggered
  22  */
  23 __chkstk:
  24 __alloca_probe:
  25
  26     /* EAX = size to be allocated */
  27     /* save the ECX register */
  28     push ecx
  29
  30     /* ECX = top of the previous stack frame */
  31     lea eax, [esp + 8]
  32
  33     /* probe the desired memory, page by page */
  34     cmp eax, PAGE_SIZE
  35     jge .l_MoreThanAPage
  36     jmp .l_LessThanAPage
  37
  38 .l_MoreThanAPage:
  39
  40     /* raise the top of the stack by a page and probe */
  41     sub ecx, PAGE_SIZE
  42     test [ecx], eax
  43
  44     /* loop if still more than a page must be probed */
  45     sub eax, PAGE_SIZE
  46     cmp eax, PAGE_SIZE
  47     jge .l_MoreThanAPage
  48
  49 .l_LessThanAPage:
  50
  51     /* raise the top of the stack by EAX bytes (size % 4096) and probe */
  52     sub ecx, eax
  53     test [ecx], eax
  54
  55     /* EAX = top of the stack */
  56     mov eax, esp
  57
  58     /* allocate the memory */
  59     mov esp, ecx
  60
  61     /* restore ECX */
  62     mov ecx, [eax]
  63
  64     /* restore the return address */
  65     mov eax, [eax + 4]
  66     push eax
  67
  68     /* return */
  69     ret
  70
  71 /* EOF */
  72 END