DOCUMENT:Q49246 06-MAY-2001 [masm] TITLE :Using OFFSET with a Group of Data Segments PRODUCT :Microsoft Macro Assembler PROD/VER::5.0,5.1,5.1a OPER/SYS: KEYWORDS: ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Macro Assembler (MASM), versions 5.1, 5.1a - Microsoft Macro Assembler (MASM), version 5.0 ------------------------------------------------------------------------------- SUMMARY ======= When using the OFFSET directive to refer to a variable defined in a SEGMENT that is part of a GROUP, the offset generated is from the beginning of the SEGMENT if full segment declarations are used. Normally when using the OFFSET directive, the offset generated is from the beginning of the GROUP when simplified segment declarations are used. This behavior occurs in Microsoft Macro Assembler (MASM) versions 5.0, 5.1, and 5.1a and in QuickAssembler versions 2.01 and 2.51. Starting with MASM 6.0 you can use the OPTION OFFSET directive to control whether the offset generated is from the beginning of the SEGMENT or from the beginning of the GROUP. MORE INFORMATION ================ The code below will demonstrate this behavior. The OFFSET directive generates an offset relative to the beginning of the SEGMENT instead of the beginning of the GROUP. When a segment override is used to specify the segment to take the address relative to, the expected offset is generated. Also, the LEA instruction generates the offset relative to the segment the DS register is assumed to. Sample Code ----------- ; Assemble options needed: none dgroup GROUP data1,data2 data1 SEGMENT PARA PUBLIC 'DATA' var1 DW 12 DUP (1) data1 ENDS data2 SEGMENT PARA PUBLIC 'DATA' var2 DW 0 data2 ENDS code SEGMENT PARA PUBLIC 'CODE' ASSUME cs:code,ds:dgroup start: mov bx, OFFSET var2 ; <--offset relative to segment mov bx, OFFSET dgroup:var2 ; <--offset relative to dgroup lea bx, var2 ; <--offset relative to ds mov ax, 4C00h int 21h code ENDS END start Additional query words: kbinf 5.00 5.10 5.10a ====================================================================== Keywords : Technology : kbMASMsearch kbAudDeveloper kbMASM510 kbMASM500 kbMASM510a Version : :5.0,5.1,5.1a ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 2001.