	    Microsoft(R) Macro Assembler Package
		      Version 5.10
	   Copyright 1988, Microsoft Corporation

Text files on the Macro Assembler disks are tabbed to save disk space. If your printer does not automatically handle tabs during printing, you must use a print program that expands tabs. For example, use the DOS PRINT program to print this and other document or source files on the disk.

	The Microsoft Macro Assembler (MASM)

Mixed-Language Support for Variables and Procedures

All EXTRN, PUBLIC, and PROC items, as well as uses of the .MODEL directive, support a language type. The language type of EXTRN and PUBLIC variables determine whether or not an underscore is prefixed to the name (an underscore is prefixed only for variables with a C language type), and the language type of a procedure determines its calling and naming conventions. For an explanation of calling and naming conventions, see the Microsoft Mixed-Language Programming Guide.

The language type consists of the word "C" or "Pascal" and uses the following syntax (lowercase items are placeholders, and bracketed items are optional):

EXTRN [<langtype>] <varname>:<type> PUBLIC [<langtype>] <varname> procName PROC [NEAR|FAR] [<langtype>] [USES <regs>,] <args>

For example, the C and Pascal keywords are used correctly in the following example:

.MODEL	SMALL,C
EXTRN	Pascal DosOpen:FAR
PUBLIC	C myVar

myOpen PROC Pascal fName:PTR, mode:WORD . . . myOpen ENDP

EVEN and ALIGN Directives

Padding for EVEN and ALIGN is now optimized. Data segments are padded with zeros. Code segments are padded with special two-byte NOP instructions where possible. The two-byte NOP consists of the instruction XCHG BX,BX (87 DB hexadecimal) which is executed faster than two one-byte NOP instructions.

/B Option Ignored

The /B option is now ignored, because its effect is irrelevant, given the new file buffering mechanism. However, the option is still accepted for the purposes of compatibility.

The PTR Operator

The PTR operator can be used to specify the size of a register indirect operand for a CALL or JMP instruction. However, the size cannot be specified with NEAR or FAR. Use WORD or DWORD instead. (In 80386 32-bit segments, use DWORD or FWORD.) Examples are shown below:

  ; 8086, 80826, or 80386 16-bit mode

  jmp  WORD PTR	[bx]	    ; Legal near jump
  call NEAR PTR	[bx]	    ; Illegal near call
  call DWORD PTR [bx]	    ; Legal far	call
  jmp  FAR PTR [bx]	    ; Illegal far jump

  ; 80386 32-bit mode only

  jmp  DWORD PTR [bx]	    ; Legal near jump
  call NEAR PTR	[bx]	    ; Illegal near call
  call FWORD PTR [bx]	    ; Legal far	call
  jmp  FAR PTR [bx]	    ; Illegal far jump

This limitation only applies to register indirect operands. NEAR or FAR can be applied to operands associated with labels. Examples are shown below:

  jmp  NEAR PTR	pointer[bx] ; Legal
  call FAR PTR location	    ; Legal

Assembler Behavior Change

Some errors and questionable practices that were ignored by earlier versions are now flagged as errors. As a result, existing source code may produce errors or warnings. The following are examples:

  - Labels defined only during pass 1 cause errors if
    used in expressions.
  - A CS ASSUME that changes from pass 1 to pass 2 causes
    an error.
  - Constants are now checked for type overflow.
  - Reserved words used	as labels produce warnings.
  - The	OFFSET operator	used with a constant causes an error.

The STACK Combine Type

The description of the STACK combine type in Section 5.2.2.3 does not explain how multiple initialized stack segments are combined. The total size of the stack is the total size of all stack definitions. LINK puts initialized data for each defined stack segment at the end of the stack. Data initialized in the last segment linked override data initialized in previous segments. This behavior is usually not relevant, since most programs only define one stack of uninitialized data. Stack data cannot be initialized with simplified segment directives.

Clarification of Parsing Error

The following error can be difficult to interpret because of the way the assembler parses (analyzes) source code:

A2015: Symbol already different kind: <name>

Typically, the assembler generates this error message when a symbol is used in a way inconsistent with how it was declared: for example, a symbol is declared as an external absolute but then used as a local code label. However, the assembler also generates this error when a symbol in the second source-code field can be interpreted as either an operation or an operand. The following example illustrates this problem:

SYM1 MACRO structName, varName varName structName <> ENDM

SYM2 STRUCT field1 DB field2 DW SYM2 ENDS

SYM1 SYM2, <mylabel>

The last line of code causes error A2015 to be generated. The assembler first looks at the second field of the line, which contains the symbol SYM2. Since SYM2 is a structure, the assembler considers SYM2 to be an operation rather than an operand, and therefore it considers SYM1 to be a label (rather than an operation). The way to avoid this error is simply code the instruction as:

SYM1 <SYM2>, <mylabel>

HIGH and LOW Operators

The HIGH and LOW operators work reliably only with constants and with offsets to external symbols. HIGH and LOW operations are not supported for offsets to local symbols.

Mixed-Mode Programming (386 Only)

When assembling code for .386 mode, the assembler now supports direct- addressing modes between segments with different USE sizes. (Segments can have the USE16 or USE32 attribute; these attributes refer to the default size of offsets.) Direct-addressing references to labels in other segments are correctly resolved. In the following example, the assembler correctly uses a 32-bit offset to access the data at label a32:

.386 SEG32 SEGMENT USE32 a32 DD ? SEG32 ENDS

SEG16 SEGMENT USE16 assume ds:seg32 mov eax,a32 SEG16 ENDS

You can also execute a CALL or a JMP to a label in a segment with a different USE size. However, the label must be declared FAR, and the CALL or JMP must not be a forward reference. The following example shows the correct method for executing such a CALL or JMP:

.386 COD16 SEGMENT USE16 'CODE' proc16 PROC FAR ret proc16 ENDP

lab16 LABEL FAR COD16 ENDS

COD32 SEGMENT USE32 'CODE' call proc16 jmp lab16 COD32 ENDS

Additional Error Messages

19 Wrong type of register

The register specified in the operand field was incompatible with the directive or instruction in the operation field. For example, the following instruction causes this error because you cannot increment the code segment:

inc cs

36 Extra NOP inserted

During pass 1 the assembler did not have enough information to correctly infer the length of the encoding for the instruction. During pass 2 the encoding was found to be shorter than the space allocated from pass 1, so one or more NOP instructions were inserted as padding. It may be possible to generate a smaller amount of code by eliminating a forward reference to a symbol.

   The Microsoft Cross-Reference Utility (CREF)

New Feature

Cross-reference listing files created with CREF now have an additional symbol. A line number followed by + indicates that a symbol is modified at the given line. For example:

  TST .	. . . .	. . . .	. . . .	.  134#	  237	 544+

The symbol TST is defined at line 134, used at line 237, and modified at line 544.

                      The Mouse Driver

If you use the Microsoft Mouse with the Microsoft CodeView(R) debugger you must have Version 6.0 or later of the Microsoft Mouse. If you do not, use the version of the MOUSE.COM driver provided in this package. Copy MOUSE.COM to the appropriate mouse directory. When you are ready to use the mouse, type

mouse

at the DOS command level. If you want to install the mouse driver automatically every time you reboot, insert the "mouse" command in your AUTOEXEC.BAT file.

Note that in earlier releases of Microsoft C, both the MOUSE.SYS and the MOUSE.COM driver were provided. If you have been using an earlier version of the MOUSE.SYS driver, delete the following line from your CONFIG.SYS file:

device=\<directory>\mouse.sys

where <directory> is the directory where the earlier mouse driver resides.

		      Microsoft CodeView Debugger

New Command-Line Option

If you have an IBM Personal System/2, then you can use the /50 command-line option to start the CodeView debugger in 50-line mode. Note that you must be in 25-line mode to effectively use either the /43 or /50 command-line option.

CONFIG.SYS Setting for CVP

To run the protected-mode CodeView debugger (CVP.EXE), you must have the following line in your CONFIG.SYS file:

IOPL=YES

Using the 7 Command in Protected Mode

If you are using OS/2 protected mode and have a math coprocessor, then you need to use a patch before you can use the CVP 7 command. To apply the patch, use the OS2PATCH.EXE and PTRACE87.PAT files that come on the same disk that CVP.EXE comes on. You also need to locate the PATCH.EXE file that comes with OS/2 and make sure that this file is in a directory listed in your PATH environment variable. Then follow these steps:

Change the current drive and directory to the root directory of the boot disk. (If the boot disk is a floppy, make sure it is inserted in the drive you used to boot from.)
Give the following command line at the DOS prompt:

OS2PATCH /A PTRACE87.PAT

Note that you may need to give the complete path names for the OS2PATCH.EXE and for the PTRACE87.PAT file. You do not n

Masm

Install / Use

README