DOCUMENT:Q39441 06-MAY-2001 [masm] TITLE :The ORG Directive and Actual Offsets PRODUCT :Microsoft Macro Assembler PROD/VER::5.1,5.1a,6.0,6.0a,6.0b OPER/SYS: KEYWORDS: ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Macro Assembler (MASM), versions 5.1, 5.1a, 6.0, 6.0a, 6.0b ------------------------------------------------------------------------------- SUMMARY ======= The ORG directive in MASM does not necessarily produce an actual offset that matches the offset specified by "ORG XXX". For example, if you use "ORG 100h" in your program, the following code will not always begin at the 100h offset relative to the start of the segment. When you are using a .COM source file and there is only one module, the "ORG 100h" will result in an actual offset of 100h for the code that follows the ORG statement. This behavior also occurs with segments with AT combine type (in which case segments are not combined by the linker, and no data or code is defined). However, if you have multiple modules and/or you are not dealing with a .COM source file, the "ORG 100h" produces an actual offset, which is somewhat greater than 100h. This behavior occurs because the linker, in these circumstances, will do some padding that you have no control over. MORE INFORMATION ================ In the following illustration (which deals with the source modules below), note that the ORG instruction increments the local offset by 100h, resulting in the offset of the PUSH instruction in example2 being 100h (that's what it would report in the listing file). However, when these modules are linked, all the portions of segment code are concatenated. Thus, EXAMPLE2.asm:code:100h is converted into code:113h. The order of concatenation is the order of linking. The following example illustrates the scenario: Actual Offset offset from start from of segment code code in module ------- --------------- +-----------------+ 0117 | ret | 0105 0116 | pop | 0103 test2.asm 0114 | mov | 0101 0113 | push | 0100 0013 | org | 0000 +-----------------+ 0012 | ret | 0004 0011 | pop | 0003 test1.asm 000F | mov | 0001 000E | push | 0000 +-----------------+ 000C | int | 000C 0009 | mov | 0009 testmain.asm 0006 | call | 0006 0003 | call | 0003 0000 | mov | 0000 +-----------------+ segment code |---------------testmain.asm: |---------------test1.asm: code segment public 'code' PUBLIC _test assume cs:code code segment public 'code' assume cs:code mov ax, 0a0ah _test proc extrn _test:proc push bp extrn _test2:proc mov bp, sp call _test pop bp call _test2 ret mov ax, 4c00h _test ENDP int 21h code ends code ends END END |---------------test2.asm: code segment public 'code' assume cs:code org 100h PUBLIC _test2 _test2 PROC push bp mov bp, sp pop bp ret _test2 ENDP code ends END Additional query words: kbinf 5.10 5.10a 6.00 6.00a 6.00b ====================================================================== Keywords : Technology : kbMASMsearch kbAudDeveloper kbMASM510 kbMASM600 kbMASM600a kbMASM510a kbMASM600b Version : :5.1,5.1a,6.0,6.0a,6.0b ============================================================================= 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.