README.DOC File
Release Notes for the Microsoft(R) Macro Assembler
Professional Development System, Version 6.1
(C) Copyright 1992, Microsoft Corporation. All rights reserved.
This document contains release notes for version 6.1 of the
Microsoft Macro Assembler Professional Development System for
MS-DOS(R). The information in this document and in the Microsoft
Advisor (online help) is more up-to-date than that in the manuals.
Microsoft improves its languages documentation at the time of
reprinting, so some of the information in this file may already be
included in your manuals.
==============================< Contents >================================
This file has 4 parts:
Part Contents
---- --------
1 Documentation Errata
2 Information on Microsoft CodeView
3 Tips for Using MASM 6.1
4 Known Assembler Bugs
====================< Part 1: Documentation Errata >======================
Reference, Page 98: LEA is no longer optimized
-------------------------------------------------
The MASM 6.1 Reference indicates that the LEA instruction is
encoded as a MOV when the source operand is a direct memory address.
In response to programmer requests, MASM 6.1 no longer performs this
optimization automatically. The optimization can be performed by
using the OPATTR operator, as shown in the following macro:
MOVLEA MACRO Dest, Symbol
IF (OPATTR(Symbol)) AND 08h
MOV Dest, OFFSET Symbol
ELSE
LEA Dest, Symbol
ENDIF
ENDM
Programmer's Guide, Page 202: User-Defined Epilogues & Prologues
--------------------------------------------------------------------
The documentation for user-defined epilogue and prologue code reads
"Your macro function must return the parmbytes parameter." It
should read "...the localbytes parameter."
Help for Runtime Error R6921
---------------------------------------
The online help for runtime error R6921 reads "...Possibly the
CONFIG.SYS file contained a line such as DEVICE=C:\OS\MM386.EXE..."
The file name should read "C:\DOS\EMM386.EXE".
===============< Part 2: Information on Microsoft CodeView >==============
CV.TXT File
--------------------
Detailed information on configuring CodeView is in the CV.TXT file,
in the directory into which you installed MASM.
CodeView and 32-bit Registers
--------------------------------------------------
CodeView 4.01 does not support single-stepping through code which
uses 32-bit registers while a DPMI server is present. Windows 3.1
and 386-MAX are examples of DPMI servers. If you need to single-
step through 32-bit code, you can exit Windows and use a VCPI server
such as EMM386.EXE to run CodeView, or use an alternate debugger
such as WDEB386 (available in the Microsoft Windows Software
Development Kit).
CodeView and .COM Files
--------------------------------------------------
CodeView 4.01 does not show source code when debugging .COM files.
If you need to view source code, build your program as a small-model
.EXE for debugging purposes.
====================< Part 3: Tips for Using MASM 6.1 >===================
Working with MASM 5.1 Code
-------------------------------------
There are differences between MASM 5.1 and MASM 6.1. Some code
written for MASM 5.1 will not assemble correctly with MASM 6.1.
Appendix A of the MASM Programmer's Guide discusses how to work
with code written for MASM 5.1.
SAMPLES.TXT File
---------------------------------------------
The file SAMPLES.TXT is installed if you choose to install the
sample code during the setup process. SAMPLES.TXT contains
information about the purpose of the samples, and about additional
tools you may need to build some of the samples.
ERRMSG.TXT File
---------------------------------------------
The file ERRMSG.TXT is installed in the directory in which you
installed MASM. This file contains information about error
messages which are not documented in the Programmer's Guide or
the MASM help files.
NMAKE and NMAKER
--------------------
MASM 6.1 includes two versions of the NMAKE project management
utility. NMAKER.EXE is a real-mode version of the utility.
NMAKE.EXE is a driver program which first loads the MS-DOS extender
into memory, and then runs NMAKER.EXE. Using the NMAKE.EXE driver
will result in faster build times. Some development tools from
other manufacturers may be incompatible with NMAKE.EXE. If you
encounter incompatibilities, use NMAKER.EXE instead.
Working With Microsoft BASIC Far Strings
---------------------------------------------
The BASIC runtime function StringAssign does not correctly handle
strings of zero length. Instead of calling StringAssign to convert
a zero-length string, simply return a near pointer to a doubleword
with the value 0.
Using Control-C to Halt Operation of MASM
-----------------------------------------------
MS-DOS applications running under DPMI, such as ML.EXE, may not
respond immediately to pressing Control-C. If you press Control-C,
and ^C appears on the screen but you are not returned to MS-DOS,
press the Enter key.
Assembling Files Generated by Compilers
------------------------------------------
Many compilers support assembly-language output. If you experience
difficulty assembling the output of such compilers, you may need to
assemble using the /Zm option. In some cases (for instance, if the
compiler inserts nondelimited comments or page numbers) it may be
necessary to edit the assembly-language output by hand.
Using MASM 6.x Structures
--------------------------------------------
MASM 6.0 and 6.1 support a more powerful syntax for structure
definition and usage than previous versions of MASM. This more
powerful syntax is enabled by default. To use the older syntax,
issue the OPTION OLDSTRUCTS directive (see Appendix A of the MASM
Programmer's Guide for more information).
Note: use of nested structures requires the new MASM 6.x syntax.
If you use nested structures, the OPTION OLDSTRUCTS directive will
be ignored for the structure which is nested.
Differences Between MASM 6.0 and MASM 6.1
--------------------------------------------
MASM 6.1 uses a different encoding for the CMP <reg8>,<reg8>
instruction than MASM 6.0 did. There is no difference in length or
processor timing.
======================< Part 4: Known Assembler Bugs >====================
Exiting from MS-DOS Critical Errors
--------------------------------------------------
MS-DOS critical errors, such as attempting to assemble a file on
a drive which does not exist or is empty, produce the "Abort, Retry
or Fail?" error message. Selecting "Abort" when running MASM in
MS-DOS may cause memory to be corrupted. This problem does not
occur when running MASM in Windows. To avoid this problem, select
"Retry" or "Fail", as appropriate.
Expression Order in High-Level Conditionals
--------------------------------------------------
Comparisons in high-level conditionals cannot begin with a literal.
For instance, this comparison causes an error:
.IF 1 == AX
but this works properly:
.IF AX == 1
Initializing Nested Structures
--------------------------------------------------
If one structure is nested within another, the inner structure's
initializer list must either be empty or include a comma between
every field. For example, the structure INFO declared on page 123
of the Programmer's Guide contains a structure of type DISKDRIVES,
which in turn contains three BYTE fields. An object of type INFO
could be initialized as:
Info1 INFO { , , , , { }} ; Inner initializer list is blank
or as:
Info1 INFO { , , , , {1, 2, }} ; Commas for all three fields
but not as:
Info1 INFO { , , , , {1, 2 }} ; Error: missing last comma
Span-Dependent Expressions used in Macros
--------------------------------------------------
MASM 6.1 evaluates macro expressions only on the first pass of
assembly, but code and data are reevaluated on subsequent passes.
Because of this, macro expressions which depend on the span between
two addresses may not evaluate correctly. For instance, the
following code will not evaluate correctly:
Label1:
JMP Label2
Label2:
REPEAT Label2 - Label1 ; Evaluates incorrectly
INC AX
ENDM
View the listing file to determine if a questionable macro expression
was evaluated as desired.
Span-Dependent Equates in Macros and EXTERNDEF ABS
---------------------------------------------------
The ABS operator causes an identifier to be exported as a relocatable
unsized constant (see Programmer's Guide page 220). If ABS is used
with EXTERNDEF within a macro, and the constant being exported
depends on the difference between two addresses, the constant may not
be exported correctly. In some cases, the listing file will show the
correct value, but the value in the resulting .obj will be incorrect.
For instance, the following code will not evaluate correctly:
EXTERNDEF TableSize:ABS ; Will not be exported correctly
MAKETABLE MACRO
Table1 LABEL BYTE
DB 0, 1, 2
TableSize EQU $-Table1
ENDM
SEG1 SEGMENT
MAKETABLE
SEG1 ENDS
To avoid this problem, either use the 'PUBLIC' directive in place of
'EXTERNDEF', or put a label before the equate, within the macro.
Span-Dependent Text Equates
--------------------------------------------------
The TEXTEQU operator is evaluated on the first assembly pass. If
TEXTEQU is used with an expression that depends on the difference
between two addresses, the resulting constant may be incorrect.
For instance, the following code will not evaluate correctly:
Label1:
JMP Label2
Label2:
WrongNum TEXTEQU %Label2-Label1 ; WrongNum will be incorrect
Using The /link /nologo Command Line Options
---------------------------------------------------------
The /link command line option for ML causes all following parameters
to be passed to the linker. If the /nologo command line option for
is passed to the linker, the linker may parse other parameters
incorrectly. To avoid this problem, use the /nologo command line
switch for ML rather than passing it to the linker. For instance,
replace:
ML hello.asm /link /nologo MYLIB.LIB
with:
ML /nologo hello.asm /link MYLIB.LIB
Alternately, you may use the NMAKE utility to automate building
your project.
RET n Does Not Generate Epilogue
---------------------------------------------------------
In MASM 5.1, using RET followed by a constant would cause epilogue
code to be generated. MASM 6.1 does not generate epilogue code in
this case.
