DOCUMENT:Q66054 06-MAY-2001 [masm] TITLE :HOWTO: Create Static Overlays with Macro Assembler PRODUCT :Microsoft Macro Assembler PROD/VER::5.1,5.1a OPER/SYS: KEYWORDS:kb16bitonly ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Macro Assembler (MASM), versions 5.1, 5.1a ------------------------------------------------------------------------------- SUMMARY ======= The Overlay Manager is a part of the run-time library of any Microsoft high-level language (C for example). One such library must be used in order to create a statically overlaid executable. Page 285 of the "Microsoft Macro Assembler 5.1 CodeView and Utilities Guide" explains the use of overlays with assembly-language modules. Only modules with a 32-bit (long) call/ret instruction can be overlaid. Routines called should be declared as FAR. The linker is unable to produce overlay modules that can be called indirectly with function pointers. The root module is the resident (nonoverlaid) portion of the program, and the overlaid module is the transient portion. If you need to modify the behavior of the Overlay Manager, the source code is available as part of the Microsoft C Run-time source code, which can be ordered through Microsoft Sales and Customer Service by calling (800) 426-9400. Note that C/C++ 7.0 and Visual C++ for Windows includes support for both static overlays and dynamic (MOVE) overlays. MORE INFORMATION ================ The following code illustrates the creation of an overlay with an assembly module. The first procedure _main in the root module calls the procedure rt2 in the overlaid module. The link line should look something like this link root (overlay); Sample Code: ------------ ; Assemble options needed: none ; main module assume cs:cseg, ds:dseg, ss:sseg DSEG SEGMENT word public line02 DB 'In the Root module' DB (13) ;CR DB (10) ;LF DB (36) ;$ String Terminator DSEG ENDS EXTRN rt2:far cseg SEGMENT byte public PUBLIC _main ; bring in C startup _main PROC FAR MOV ax, DSEG MOV ds, ax MOV ah, 09 ;String output Function 09H MOV dx, seg line02 MOV ds, dx MOV dx, offset line02 INT 21h ;Invoking DOS Interrupt 21H CALL rt2 ;Call to the Overlay Procedure MOV ah, 4Ch ;Function 4CH return to DOS INT 21h _main ENDP cseg ENDS sseg SEGMENT stack DB 20 dup (0) sseg ENDS END ------------------------------------ ; overlaid module D1SEG SEGMENT word public line03 DB 'In the Overlaid module' DB (13) DB (10) DB (36) D1SEG ENDS PUBLIC rt2 c1seg SEGMENT byte public rt2 PROC FAR MOV ax, D1SEG MOV ds,ax MOV ah,09 MOV dx,seg line03 MOV ds,dx MOV dx,offset line03 INT 21h RET rt2 ENDP c1seg ENDS END Additional query words: ====================================================================== Keywords : kb16bitonly Technology : kbMASMsearch kbAudDeveloper kbMASM510 kbMASM510a Version : :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.