Source code of Windows XP (NT5)
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/*++
Copyright (c) 2001 Microsoft Corporation
Module Name:
alloca.h
Abstract:
This module implements a safe stack-based allocator with fallback to the heap.
Author:
Jonathan Schwartz (JSchwart) 16-Mar-2001
Revision History:
--*/
#ifndef _SAFEALLOCA_H_
#define _SAFEALLOCA_H_
#ifdef __cplusplus
extern "C"
{
#endif // __cplusplus
#include <align.h> // ALIGN_WORST
//
// Type definitions
//
typedef ULONG SAFEALLOCA_HEADER;
typedef PVOID (APIENTRY *SAFEALLOC_ALLOC_PROC)(
SIZE_T Size
);
typedef VOID (APIENTRY *SAFEALLOC_FREE_PROC)(
PVOID BaseAddress
);
//
// Constant definitions
//
#define SAFEALLOCA_STACK_HEADER ((SAFEALLOCA_HEADER) 0x6b637453) /* "Stck" */
#define SAFEALLOCA_HEAP_HEADER ((SAFEALLOCA_HEADER) 0x70616548) /* "Heap" */
#define SAFEALLOCA_USE_DEFAULT 0xdeadbeef
//
// We'll be adding ALIGN_WORST bytes to the allocation size to add room for
// the SAFEALLOCA_HEADER -- make sure we'll always have enough space.
//
C_ASSERT(sizeof(SAFEALLOCA_HEADER) <= ALIGN_WORST);
//
// Per-DLL SafeAlloca globals
//
extern SIZE_T g_ulMaxStackAllocSize;
extern SIZE_T g_ulAdditionalProbeSize;
extern SAFEALLOC_ALLOC_PROC g_pfnAllocate;
extern SAFEALLOC_FREE_PROC g_pfnFree;
//
// Functions defined in alloca.lib
//
VOID
SafeAllocaInitialize(
IN OPTIONAL SIZE_T ulMaxStackAllocSize,
IN OPTIONAL SIZE_T ulAdditionalProbeSize,
IN OPTIONAL SAFEALLOC_ALLOC_PROC pfnAllocate,
IN OPTIONAL SAFEALLOC_FREE_PROC pfnFree
);
BOOL
VerifyStackAvailable(
SIZE_T Size
);
//
// Usage:
//
// VOID
// SafeAllocaAllocate(
// PVOID PtrVar,
// SIZE_T BlockSize
// );
//
// (PtrVar == NULL) on failure
//
#define SafeAllocaAllocate(PtrVar, BlockSize) \
\
{ \
PVOID *ppvAvoidCast = (PVOID *) &(PtrVar); \
\
(PtrVar) = NULL; \
\
/* Make sure block is below the threshhold and that the probe won't overflow */ \
\
if ((BlockSize) <= g_ulMaxStackAllocSize \
&& \
((BlockSize) + g_ulAdditionalProbeSize >= (BlockSize))) \
{ \
if (VerifyStackAvailable((BlockSize) \
+ g_ulAdditionalProbeSize \
+ ALIGN_WORST)) \
{ \
/* \
* Don't need to wrap with try-except since we just probed \
*/ \
\
*ppvAvoidCast = _alloca((BlockSize) + ALIGN_WORST); \
} \
\
if ((PtrVar) != NULL) \
{ \
*((SAFEALLOCA_HEADER *) (PtrVar)) = SAFEALLOCA_STACK_HEADER; \
*ppvAvoidCast = ((LPBYTE) (PtrVar) + ALIGN_WORST); \
} \
} \
\
/* \
* Stack allocation failed -- try the heap \
*/ \
\
if ((PtrVar) == NULL) \
{ \
*ppvAvoidCast = g_pfnAllocate((BlockSize) + ALIGN_WORST); \
\
if ((PtrVar) != NULL) \
{ \
*((SAFEALLOCA_HEADER *) (PtrVar)) = SAFEALLOCA_HEAP_HEADER; \
*ppvAvoidCast = ((LPBYTE) (PtrVar) + ALIGN_WORST); \
} \
} \
}
//
// Usage:
//
// VOID
// SafeAllocaFree(
// PVOID PtrVar,
// );
//
#define SafeAllocaFree(PtrVar) \
\
if (PtrVar != NULL) \
{ \
SAFEALLOCA_HEADER *Tag = (SAFEALLOCA_HEADER *) ((LPBYTE) (PtrVar) \
- ALIGN_WORST); \
\
if (*(SAFEALLOCA_HEADER *) (Tag) == SAFEALLOCA_HEAP_HEADER) \
{ \
g_pfnFree(Tag); \
} \
else \
{ \
ASSERT(*(SAFEALLOCA_HEADER *) (Tag) == SAFEALLOCA_STACK_HEADER); \
} \
}
#ifdef __cplusplus
}
#endif // __cplusplus
#endif // _SAFEALLOCA_H_