Using Full Segment Directives with MASM 6.0 HELLO.ASM

• Microsoft Macro Assembler for OS/2, version 6.0, 6.0a, and 6.0b

SUMMARY

The "Microsoft Macro Assembler Programmer's Guide" for MASM version 6.0 has a HELLO.ASM example for OS/2 on page 458, section 17.3, and has the same example using INVOKE on page 459. Both examples use simplified dot directives. The code sample below shows how the examples may be assembled using full segment directives.

MORE INFORMATION

The code that the assembler generates with the INVOKE directive is placed in comment lines below each INVOKE.

With INVOKE, the assembler generates code depending on the prototypes for the DosWrite and DosExit functions declared in the include file BSEDOS.INC. Both the prototypes indicate the PASCAL calling convention. In BSEDOS.INC, DosWrite is prototyped as:

   DosWrite PROTO FAR PASCAL \
            hf:Hfile, bBuf:PVOID, cbBuf:WORD, pcbBytesWritten:PWORD

   DosExit PROTO FAR PASCAL fTerminate:BOOL, usExitCode:WORD

   PVOID TYPEDEF FAR PTR

   PWORD TYPEDEF FAR PTR WORD

   BOOL TYPEDEF WORD

1. Pushes the arguments for the function DosWrite on the stack (from right to left).

2. Pushes the arguments for the DosExit function on the stack (from right to left).

3. Exits.

Sample Code

; Assemble options needed: none

       .286

       INCLUDELIB os2.lib
       INCLUDE os2.inc

STACK  SEGMENT PARA STACK 'STACK'     ;stack segment declared
       WORD   256 dup(?)

_DATA      SEGMENT WORD PUBLIC 'DATA'     ;data segment declared
message    BYTE  "Hello World", 13,10

_DATA      ENDS

_TEXT  SEGMENT WORD PUBLIC 'CODE'     ;code segment declared
       ASSUME   CS:_TEXT, DS:_DATA, SS:STACK

       INVOKE DosWrite, 1, ADDR message, LENGTHOF message
                           ADDR bytecount

       ;Code generated by INVOKE
       ;------------------------
       ;   push   1                   ;output to Stdout
       ;   push   ds                  ;pass address of msg
       ;   push   OFFSET message
       ;   push   LENGTHOF message    ;pass length of msg
       ;   push   ds
       ;   push   OFFSET bytecount    ;pass address of count
       ;   call   DosWrite

       INVOKE   DosExit,+1h, +0h

       ;Code generated by INVOKE
       ;------------------------
       ;   push   +1h                 ;Ends all threads
       ;   push   +0h                 ;Pass 0 return code
       ;   call   DosExit

       END @Startup