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Q30500: Segment Relative Versus Group Relative

Article: Q30500
Product(s): Microsoft Macro Assembler
Version(s): 5.1
Operating System(s): 
Keyword(s): 
Last Modified: 04-MAY-2001

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The information in this article applies to:

- Microsoft Macro Assembler (MASM), version 5.1 
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SUMMARY
=======

The following sample code will be used to explain segment relative and group
relative:

     dgroup  GROUP   aseg,cseg
     ASSUME  cs:dgroup,ds:dgroup
     aseg    SEGMENT public  byte    'CODE'
             org 100h
             start:
             data_pointer    dw  the_data
     aseg    ends
     cseg    SEGMENT public  byte    'CODE'
             the_data    label   byte
     cseg    ends
             end start

When defining data, fixups are relative to the start of the segment. The variable
data_pointer will have an address relative to the start of the aseg segment. If
you want the variable to have an address relative to the start of the group, you
can explicitly state the offset relative to dgroup as follows.

     data_pointer    dw  offset  dgroup:the_data

The exception is when you are using simplified segment directives. In that case,
group relative fixups always are used rather than segment relative.

In code segments, fixups are relative to either segment or group depending on the
ASSUME statements. In other words, the ASSUME STATEMENT is checked before the
fixup is generated. The exception here is the same as above. When using
simplified segment directives, group relative fixups are the default.

The OFFSET operator is segment relative and is discussed further in the following
article in the Microsoft Knowledge Base:

  Q30517 OFFSET Operator Is Segment Relative

Additional query words: 5.10

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Keywords          :  
Technology        : kbMASMsearch kbAudDeveloper kbMASM510
Version           : :5.1

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