page ,132 title chkstk - C stack checking routine ;*** ;chkstk.asm - C stack checking routine ; ; Copyright (c) 1985-1997, Microsoft Corporation. All rights reserved. ; ;Purpose: ; Provides support for automatic stack checking in C procedures ; when stack checking is enabled. ; ;******************************************************************************* .xlist include cruntime.inc .list ; size of a page of memory _PAGESIZE_ equ 1000h CODESEG page ;*** ;_chkstk - check stack upon procedure entry ; ;Purpose: ; Provide stack checking on procedure entry. Method is to simply probe ; each page of memory required for the stack in descending order. This ; causes the necessary pages of memory to be allocated via the guard ; page scheme, if possible. In the event of failure, the OS raises the ; _XCPT_UNABLE_TO_GROW_STACK exception. ; ; NOTE: Currently, the (EAX < _PAGESIZE_) code path falls through ; to the "lastpage" label of the (EAX >= _PAGESIZE_) code path. This ; is small; a minor speed optimization would be to special case ; this up top. This would avoid the painful save/restore of ; ecx and would shorten the code path by 4-6 instructions. ; ;Entry: ; EAX = size of local frame ; ;Exit: ; ESP = new stackframe, if successful ; ;Uses: ; EAX ; ;Exceptions: ; _XCPT_GUARD_PAGE_VIOLATION - May be raised on a page probe. NEVER TRAP ; THIS!!!! It is used by the OS to grow the ; stack on demand. ; _XCPT_UNABLE_TO_GROW_STACK - The stack cannot be grown. More precisely, ; the attempt by the OS memory manager to ; allocate another guard page in response ; to a _XCPT_GUARD_PAGE_VIOLATION has ; failed. ; ;******************************************************************************* labelP _alloca_probe, PUBLIC labelP _chkstk, PUBLIC push ecx ; save ecx cmp eax,_PAGESIZE_ ; more than one page requested? lea ecx,[esp] + 8 ; compute new stack pointer in ecx ; correct for return address and ; saved ecx jb short lastpage ; no ;------------ probepages: sub ecx,_PAGESIZE_ ; yes, move down a page sub eax,_PAGESIZE_ ; adjust request and... test dword ptr [ecx],eax ; ...probe it cmp eax,_PAGESIZE_ ; more than one page requested? jae short probepages ; no lastpage: sub ecx,eax ; move stack down by eax mov eax,esp ; save current tos and do a... test dword ptr [ecx],eax ; ...probe in case a page was crossed mov esp,ecx ; set the new stack pointer mov ecx,dword ptr [eax] ; recover ecx mov eax,dword ptr [eax + 4] ; recover return address push eax ; prepare return address ; ...probe in case a page was crossed ret end