.MODEL Directive Forces DOSSEG Segment Ordering in MASM

• Microsoft Macro Assembler for MS-DOS, version 5.0, 5.1, 5.1a, 6.0, 6.0a, 6.0b, and 6.11
• Microsoft Macro Assembler for OS/2, versions 5.1, 5.1a, 6.0, 6.0a, and 6.0b

SUMMARY

The .MODEL assembler directive forces the segments in the resulting executable program to be ordered as if the DOSSEG directive had been used. This will override any other directives used to organize segments in an executable program. The code below demonstrates this behavior.

Because of this, the options below will be ignored:

   /A and /S command line switches
   .ALPHA and .SEQ assembler directives

This behavior is also true with QuickAssembler versions 2.01 and 2.51. The .MODEL assembler directive was designed for use in mixed-language programming. Because of this, it will automatically order the segments in a way compatible with the way higher-level language compilers order them. This will happen even if the <,language> option on the .MODEL directive is not used.

MORE INFORMATION

The map file created from the linker is included below.

Map file:

Start  Stop   Length Name                        Class
00000H 00000H 00000H _TEXT                       CODE
00000H 00002H 00003H B                           CODE
00004H 00004H 00000H _DATA                       DATA
00004H 00005H 00002H A                           DATA
00010H 0010FH 00100H STACK                       STACK

Origin   Group
0000:0   DGROUP

Start  Stop   Length Name                        Class
00000H 00001H 00002H A                           DATA
00002H 00004H 00003H B                           CODE

Sample Code

; Assemble options needed: none

.MODEL medium .286 .SEQ .STACK 100h

A SEGMENT WORD PUBLIC 'DATA' test_data DW 10 A ENDS

B SEGMENT WORD PUBLIC 'CODE'

    mov ax, 1

END