Creating 32-Bit Flat Memory Model MASM Code for OS/2 2.0

The information in this article applies to:

• Microsoft Macro Assembler for MS-DOS and OS/2, versions 6.0, 6.0a, 6.0b

SUMMARY

Versions 6.0, 6.0a, and 6.0b of the Microsoft Macro Assembler (MASM) provide the .MODEL flat directive to support generating 32-bit flat memory model applications. When combined with the LINK386 utility and DOSCALLS.LIB library provided with OS/2 version 2.0, you can generate a 32-bit flat memory model application for the OS/2 version 2.0 environment.

To build a 32-bit flat memory model application for OS/2 2.0, perform the following four steps:

1. Place the INCLUDELIB DOSCALLS.LIB directive in each source module that contains a call into the OS/2 2.0 application programming interface (API). DOSCALLS.LIB is the OS/2 2.0 import library that supports application calls to the operating system.

2. Place the .386 or .486 directive before the .MODEL flat, syscall directive to ensure that your code and data segments are set up correctly for a 32-bit flat memory model application. The order in which these two directives appear in the source code is important.

3. Specify the /c assembler option flag on the assembler command line to prevent MASM from invoking its 16-bit linker.

4. Link the object files using LINK386 distributed with OS/2 2.0. If LINK386 cannot find the DOSCALLS.LIB file, specify the path to the library.

MORE INFORMATION

The LINK386 utility and DOSCALLS.LIB library are provided by IBM with OS/2 version 2.0. MASM versions 6.0, 6.0a, and 6.0b does not include either the required library support for OS/2 operating system calls or a linker capable of producing flat memory model applications. For more information on LINK386, DOSCALLS.LIB, or the functions of the OS/2 2.0 API, please contact IBM.

LINK386 may generate two warnings that can be safely ignored:

   LINK386: warning L4071: application type not specified:
      assuming WINDOWCOMPAT
   LINK386: warning L4071: no automatic data segment

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Sample Code

; Assemble options needed: /c

INCLUDELIB DOSCALLS.LIB

.386 .MODEL flat, syscall

Dos32Write PROTO NEAR32 syscall,

    hf:WORD, pvBuf:NEAR32, cbBuf:WORD, pcbBytesWritten:NEAR32

    fTerminate:WORD, ulExitCode:WORD

.DATA

msg DB "Hello, world.", 13, 10 written DW 0

.CODE _start:

    INVOKE  Dos32Write,        ; OS/2 system call
        1,                     ; File handle for screen
        NEAR32 PTR msg,        ; Address of string
        LENGTHOF msg,          ; Length of string
        NEAR32 PTR written     ; Bytes written

    INVOKE  Dos32Exit,         ; OS/2 system call
        0,                     ; Terminate all threads
        0                      ; Result code for parent process