.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 FRAME declaration to the .ENDPROLOG 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.

For more information, see MASM for x64 (ml64.exe).

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
MASM BNF Grammar