72 lines
2.1 KiB
NASM
72 lines
2.1 KiB
NASM
page ,132
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title alloca16 - aligned C stack checking routine
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;***
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;chkstk.asm - aligned C stack checking routine
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;
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; Copyright (c) Microsoft Corporation. All rights reserved.
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;
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;Purpose:
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; Provides 16 and 8 bit aligned alloca routines.
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;
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;*******************************************************************************
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.xlist
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include cruntime.inc
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.list
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extern _chkstk:near
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; size of a page of memory
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CODESEG
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page
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;***
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; _alloca_probe_16, _alloca_probe_8 - align allocation to 16/8 byte boundary
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;
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;Purpose:
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; Adjust allocation size so the ESP returned from chkstk will be aligned
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; to 16/8 bit boundary. Call chkstk to do the real allocation.
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;
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;Entry:
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; EAX = size of local frame
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;
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;Exit:
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; Adjusted EAX.
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;
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;Uses:
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; EAX
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;
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;*******************************************************************************
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public _alloca_probe_8
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_alloca_probe_16 proc ; 16 byte aligned alloca
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push ecx
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lea ecx, [esp] + 8 ; TOS before entering this function
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sub ecx, eax ; New TOS
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and ecx, (16 - 1) ; Distance from 16 bit align (align down)
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add eax, ecx ; Increase allocation size
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sbb ecx, ecx ; ecx = 0xFFFFFFFF if size wrapped around
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or eax, ecx ; cap allocation size on wraparound
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pop ecx ; Restore ecx
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jmp _chkstk
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alloca_8: ; 8 byte aligned alloca
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_alloca_probe_8 = alloca_8
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push ecx
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lea ecx, [esp] + 8 ; TOS before entering this function
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sub ecx, eax ; New TOS
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and ecx, (8 - 1) ; Distance from 8 bit align (align down)
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add eax, ecx ; Increase allocation Size
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sbb ecx, ecx ; ecx = 0xFFFFFFFF if size wrapped around
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or eax, ecx ; cap allocation size on wraparound
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pop ecx ; Restore ecx
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jmp _chkstk
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_alloca_probe_16 endp
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end
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