OFFSET Always Returns the END of a Segment Name (75276)

SUMMARY

With the release of the Microsoft Macro Assembler (MASM) version 6.0, the OFFSET operator applied to a segment name now returns the end of the segment relative to the start of the segment.

This is a change from MASM versions 5.x where "OFFSET segname" will return the beginning of the segment if it is declared class 'CODE'. If the segment is declared of some other class, "OFFSET segname" will return either the end of the segment relative to the beginning of a segment if full segment definitions are used, or the end of the segment relative to the start of the group the segment was contained in if simplified directives are used.

MORE INFORMATION

As part of defining the BNF for MASM 6.0, an attempt was made to remove any ambiguities in the language. This is one of those changes. In MASM 6.0, "OFFSET segname" will always return the end of the segment unless an explicit group or segment override is provided.

For example,

_DATA segment  para PUBLIC 'data'
      db    dup 100 ( )
_DATA ends

STACK segment  para STACK 'stack'
      db    dup 100 (?)
STACK ends

DGROUP group _DATA, STACK

TEXT  segment para 'CODE'
      ORG   100

      mov   sp, OFFSET STACK          ; mov's 100 into sp
      mov   sp, OFFSET DGROUP:STACK   ; mov's 200 into sp

      mov   ax, OFFSET TEXT           ; mov's size of TEXT into AX
      mov   ax, OFFSET TEXT:0         ; mov's start of TEXT into AX

For more information on the OFFSET operator, see the online Help.