---
title: ".ALLOCSTACK"
ms.custom: ""
ms.date: "10/28/2016"
ms.prod: "visual-studio-dev14"
ms.reviewer: ""
ms.suite: ""
ms.technology: 
  - "devlang-cpp"
ms.tgt_pltfrm: ""
ms.topic: "article"
f1_keywords: 
  - ".ALLOCSTACK"
dev_langs: 
  - "C++"
helpviewer_keywords: 
  - ".ALLOCSTACK directive"
ms.assetid: 9801594b-7ac2-4df2-a49d-07d9dd9af99e
caps.latest.revision: 9
author: "corob-msft"
ms.author: "corob"
manager: "ghogen"
translation.priority.ht: 
  - "cs-cz"
  - "de-de"
  - "es-es"
  - "fr-fr"
  - "it-it"
  - "ja-jp"
  - "ko-kr"
  - "pl-pl"
  - "pt-br"
  - "ru-ru"
  - "tr-tr"
  - "zh-cn"
  - "zh-tw"
---
# .ALLOCSTACK
Generates a **UWOP_ALLOC_SMALL** or a **UWOP_ALLOC_LARGE** with the specified size for the current offset in the prologue.  
  
## Syntax  
  
```  
.ALLOCSTACK size  
```  
  
## Remarks  
 MASM will choose the most efficient encoding for a given size.  
  
 .ALLOCSTACK allows ml64.exe users to specify how a frame function unwinds and is only allowed within the prologue, which extends from the [PROC](../../assembler/masm/proc.md) FRAME declaration to the [.ENDPROLOG](../../assembler/masm/dot-endprolog.md) directive. These directives do not generate code; they only generate `.xdata` and `.pdata`. .ALLOCSTACK should be preceded by instructions that actually implement the actions to be unwound. It is a good practice to wrap both the unwind directives and the code they are meant to unwind in a macro to ensure agreement.  
  
 The `size` operand must be a multiple of 8.  
  
 Fore more information, see [MASM for x64 (ml64.exe)](../../assembler/masm/masm-for-x64-ml64-exe.md).  
  
## Sample  
 The following sample shows how to specify an unwind/exception handler:  
  
```  
; ml64 ex3.asm /link /entry:Example1  /SUBSYSTEM:Console  
text SEGMENT  
PUBLIC Example3  
PUBLIC Example3_UW  
Example3_UW PROC NEAR  
   ; exception/unwind handler body  
  
   ret 0  
  
Example3_UW ENDP  
  
Example3 PROC FRAME : Example3_UW  
  
   sub rsp, 16  
.allocstack 16  
  
.endprolog  
  
   ; function body  
    add rsp, 16  
   ret 0  
  
Example3 ENDP  
text ENDS  
END  
```  
  
## See Also  
 [Directives Reference](../../assembler/masm/directives-reference.md)