reactos/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 .globl __chkstk
  11 .globl __alloca_probe
  12
  13 /*
  14  _chkstk() is called by all stack allocations of more than 4 KB. It grows the
  15  stack in areas of 4 KB each, trying to access each area. This ensures that the
  16  guard page for the stack is hit, and the stack growing triggered
  17  */
  18 __chkstk:
  19 __alloca_probe:
  20
  21 /* EAX = size to be allocated */
  22 /* save the ECX register */
  23  pushl %ecx
  24
  25 /* ECX = top of the previous stack frame */
  26  leal 8(%esp), %ecx
  27
  28 /* probe the desired memory, page by page */
  29  cmpl $0x1000, %eax
  30  jge .l_MoreThanAPage
  31  jmp .l_LessThanAPage
  32
  33 .l_MoreThanAPage:
  34
  35 /* raise the top of the stack by a page and probe */
  36  subl $0x1000, %ecx
  37  testl %eax, 0(%ecx)
  38
  39 /* loop if still more than a page must be probed */
  40  subl $0x1000, %eax
  41  cmpl $0x1000, %eax
  42  jge .l_MoreThanAPage
  43
  44 .l_LessThanAPage:
  45
  46 /* raise the top of the stack by EAX bytes (size % 4096) and probe */
  47  subl %eax, %ecx
  48  testl %eax, 0(%ecx)
  49
  50 /* EAX = top of the stack */
  51  movl %esp, %eax
  52
  53 /* allocate the memory */
  54  movl %ecx, %esp
  55
  56 /* restore ECX */
  57  movl 0(%eax), %ecx
  58
  59 /* restore the return address */
  60  movl 4(%eax), %eax
  61  pushl %eax
  62
  63 /* return */
  64  ret
  65
  66 /* EOF */