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// TITLE("C-Runtime Stack Checking")
//++
//
// Copyright (c) 1993,1994 IBM Corporation
//
// Module Name:
//
// chkstk.s
//
// Abstract:
//
// This module implements runtime stack checking.
//
// Author:
//
// Mark D. Johnson
//
// Environment:
//
// User/Kernel mode.
//
// Revision History:
//
//--
#include <ksppc.h>
SBTTL("Check Stack")
//++
//
// VOID _RtlCheckStack(in ULONG n_alloc)
//
// Routine Description:
//
// This function provides runtime stack checking for local allocations
// that are more than a page and for storage dynamically allocated with
// the alloca function. Stack checking consists of probing downward in
// the stack a page at a time. If the current stack commitment is exceeded,
// then the system will automatically attempt to expand the stack. If the
// attempt succeeds, then another page is committed. Otherwise, a stack
// overflow exception is raised. It is the responsiblity of the caller to
// handle this exception.
//
// Two entry points are supported. The first/standard entry point
// calls for n_alloc to be passed as single argument (in r.3). In
// the second case, the single argument is the negative of the amount
// requested (the amount by which to decrement the stack pointer), and
// is passed in r.12.
//
// Registers r.0 and r.11 are modified.
//
// Arguments:
//
// n_alloc(r.3/r.12) - Supplies the size of the allocation on the stack.
// With standard entry, passed in r.3. In alternate
// entry, passed in r.12. In the latter case (r.12)
// the value supplied is the quanitity by which to
// decrement r.sp (a negative value).
//
// Return Value:
//
// None.
//
// Assumptions:
//
// The value of Teb_Ptr is provided in r.13.
//
// The bottom of stack "bot" (r.11) is multiple of PAGE_SIZE.
//
//
// low
// :
// | :
// | |
// | |
// |.......|<--- r.sp + r.12 - (PAGE_SIZE-1)
// | ^ |
// | |< -|- - - - - - always < PAGE_SIZE
// | v |
// +-------+<--- bot - m*PAGE_SIZE
// | |
// | : |
// | |
// +-------+<--- r.sp + r.12
// | |
// | |
// | |
// | : |
// | : |
// | : |
// | : |
// | |
// | |
// | |
// | |
// +=======+<--- bottom of stack "bot" (r.11)
// | |
// | |
// | |
// | : |
// | : |
// | : |
// | |
// | |
// +-------+<--- r.sp
// | |
// | |
// | : |
// | :
// | : high
// : m is count for add'l pages to commit
//
//
// m:=max(0,{bot-[(r.sp+r.12)-(PAGE_SIZE-1)]}/PAGE_SIZE)
// =max(0,bot-[r.12-(PAGE_SIZE-1)+r.sp])/PAGE_SIZE
//
// Operands in expression [r.12-(PAGE_SIZE-1)+r.sp) are known upon entry
// to routine. This intermediate quantity is calculated early in r.0.
.text
.align 5
// want entry for _RtlCheckStack aligned on a 2**5-1 byte boundary so that
// more commonly used (internal) entry _RtlCheckStack.12 is aligned on
// 2**5 byte (cache-line) boundary ... and most often used code fits in
// single cache-line
or r.11, r.11, r.11; or r.11, r.11, r.11
or r.11, r.11, r.11; or r.11, r.11, r.11
or r.11, r.11, r.11; or r.11, r.11, r.11
or r.11, r.11, r.11; or r.11, r.11, r.11
or r.11, r.11, r.11; or r.11, r.11, r.11
or r.11, r.11, r.11; or r.11, r.11, r.11
or r.11, r.11, r.11; or r.11, r.11, r.11
or r.11, r.11, r.11
LEAF_ENTRY(_RtlCheckStack)
neg r.12,r.3
ALTERNATE_ENTRY(_RtlCheckStack.12)
// r.13 contains the TEB pointer
lwz r.11,TeStackLimit(r.13) // Get low stack address
// r.11 contains "bot" of stack
subi r.0,r.12,(PAGE_SIZE-1)
add r.0,r.0,r.sp
// r.0 is desired "bot"
sub r.0,r.11,r.0
srawi. r.0,r.0,PAGE_SHIFT // Number pages to add/commit
blelr // if <=0, return
mtctr r.0
PageLoop:
// Attempt to commit pages beyond the limit
lwzu r.0,-PAGE_SIZE(r.11)
bdnz PageLoop
LEAF_EXIT(_RtlCheckStack)
.debug$S
.ualong 1
.uashort 52
.uashort 0x205 // S_GPROC32
.ualong 0
.ualong 0
.ualong 0
.ualong _RtlCheckStack.end-.._RtlCheckStack
.ualong 0
.ualong _RtlCheckStack.end-.._RtlCheckStack
.ualong [secoff].._RtlCheckStack
.uashort [secnum].._RtlCheckStack
.uashort 0x1000
.byte 0x00
.byte 16, ".._RtlCheckStack"
.uashort 29
.uashort 0x209 // S_LABEL32
.ualong [secoff].._RtlCheckStack.12
.uashort [secnum].._RtlCheckStack.12
.byte 0
.byte 19, ".._RtlCheckStack.12"
.uashort 2, 0x6 // S_END
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