Q82287: FIX: MASM 6.0 Does Not Align on Page Boundary
Article: Q82287
Product(s): Microsoft Macro Assembler
Version(s): 6.0,6.0a,6.0b
Operating System(s):
Keyword(s):
Last Modified: 06-MAY-2001
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The information in this article applies to:
- Microsoft Macro Assembler (MASM), versions 6.0, 6.0a, 6.0b
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SYMPTOMS
========
When using the Microsoft Macro Assembler (MASM), the ALIGN directive does not
work properly when attempting to place data or code on a page (256 byte)
boundary. If aligning inside of a code segment, the "ALIGN 256" directive has no
effect on the placement of subsequent instructions; it may insert 256 bytes
somewhere else later in that segment. When aligning inside of a data segment,
the data to be aligned is placed 1 byte past the page boundary.
RESOLUTION
==========
To work around this problem, follow the steps below:
1. Edit your source to use an "ALIGN 128" where you previously used "ALIGN 256".
For example,
. .
. .
XOR AL,AL XOR AL,AL
ALIGN 256 ---> ALIGN 128
MOV CX,5 MOV CX,5
. .
. .
2. Assemble your source with the options "/Fl /c". This will generate a listing
file with the same base name of your source file and a .LST extension.
3. Viewing the .LST file, locate the line of code you want to align. The value
to the left of your source code represents the offset of that item in the
relative segment. This value will be a multiple of 128 (80h). There is a
possibility that this value will fall on a page frame (100h). If this is the
case then the code is aligned on a 256-byte boundary and you are done.
Offset Machine Code Source Code
------ ------------ -----------
.
.
0000 32 C0 XOR AL,AL
ALIGN 128
0080 B9 0005 MOV CX,5 **Not Aligned on page**
.
.
.
.
0000 32 C0 XOR AL,AL
ALIGN 128
0100 B9 0005 MOV CX,5 **Aligned on page**
.
.
4. If the offset value is not a multiple of 256, go back to your source file and
add the line "DB 128 DUP(?)" beneath the "ALIGN 128" line. This will add the
bytes necessary to align your code to a page frame. Reassemble with "/Fl /c"
and view the .LST file to verify.
. .
. .
XOR AL,AL XOR AL,AL
ALIGN 128 ---> ALIGN 128
DB 128 DUP(?)
MOV CX,5 MOV CX,5
. .
. .
STATUS
======
Microsoft has confirmed this to be a problem in MASM versions 6.0, 6.0a, and
6.0b. This problem was corrected in MASM for MS-DOS version 6.1.
MORE INFORMATION
================
The following sample code can be used to demonstrate the problem.
Sample Code
-----------
; Assemble options needed: none
_TEST SEGMENT PAGE PUBLIC 'CODE'
start:
xor al, al
ALIGN 256
xor al, al
mov ax,4C00h
int 21h
_TEST ENDS
END start
Additional query words: 6.00 6.00a 6.00b buglist6.00 buglist6.00a buglist6.00b fixlist6.10
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Keywords :
Technology : kbMASMsearch kbAudDeveloper kbMASM600 kbMASM600a kbMASM600b
Version : :6.0,6.0a,6.0b
Solution Type : kbfix
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