Using Common Address Space

Listing 16.4 provides the code of a DLL and a program calling a procedure from this library. In this program, there isn't anything especially difficult. The main goal of this example is to demonstrate that the primary process and the DLL share the same address space. The process passes addresses of strings located in the data block of the primary process. The procedure, in turn , returns to the primary process the address of the string that resides in the DLLs block of data.

Listing 16.4: Passing parameters between the main module and the dynamic link library

 ; DLL2.ASM .586P ; Flat memory model IFDEF MASM  .MODEL FLAT, stdcall ELSE  .MODEL FLAT ENDIF PUBLIC DLLP1 ; Constants ; Messages that arrive when ; the DLL is opened DLL_PROCESS_DETACH   equ 0 DLL_PROCESS_ATTACH   equ 1 DLL_THREAD_ATTACH    equ 2 DLL_THREAD_DETACH    equ 3 IFDEF MASM ; MASM ; Prototypes of external procedures        EXTERN      MessageBoxA@16:NEAR ; INCLUDELIB directives for the linker        includelib c:\masm32\lib\user32.lib        includelib c:\masm32\lib\kernel32.lib ELSE ; TASM        EXTERN     MessageBoxA:NEAR        MessageBoxA@16 = MessageBoxA        includelib c:\tasm32\lib\import32.lib ENDIF ;---------------------------------------------- ; Data segment _DATA SEGMENT        TEXT DB "String in a DLL", 0 _DATA ENDS ; Code segment __TEXT SEGMENT ; [EBP+10H]   ; Reserved parameter ; [EBP+0CH]   ; Cause of the call ; [EBP+8]     ; DLL module identifier DLLENTRY:        MOV    FAX, DWORD PTR [EBP+0CH]        CMP    FAX, 0        JNE    DL ; Close the library        JMP    _EXIT D1:        CMP    FAX, 1        JNE    _EXIT ; Open the library _EXIT:        MOV    FAX, 1        RET    12 ;------------------ ; Parameter addesses ; [EBP+8] ; [EBP+0CH] DLLP1 PROC EXPORT        PUSH   EBP        MOV    EBP, ESP        PUSH   0        PUSH   DWORD PTR [EBP+0CH]        PUSH   DWORD PTR [EBP+8]        PUSH   0        CALL   MessageBoxA@16        POP    EBP        LEA    EAX, TEXT        RET    8 DLLP1 ENDP _TEXT ENDS END DLLENTRY ; Main module DLLEX2.ASM that calls ; a procedure from the DLL .586P ; Flat memory model .MODEL FLAT, stdcall ; Constants ; Prototypes of external procedures IFDEF MASM ; MASM        EXTERN      GetProcAddress@8:NEAR        EXTERN      LoadLibraryA@4:NEAR        EXTERN      FreeLibrary@4:NEAR        EXTERN      ExitProcess@4:NEAR        EXTERN      MessageBoxA@16:NEAR        includelib c:\masm32\lib\user32.lib        includelib c:\masm32\lib\kernel32.lib ELSE ; TASM        includelib c:\tasm32\lib\import32.lib        EXTERN      GetProcAddress:NEAR        EXTERN      LoadLibraryA:NEAR        EXTERN      FreeLibrary:NEAR        EXTERN      ExitProcess:NEAR        EXTERN      MessageBoxA:NEAR        GetProcAddress@8 = GetProcAddress        LoadLibraryA@4 = LoadLibraryA        FreeLibrary@4 = FreeLibrary        ExitProcess@4 = ExitProcess        MessageBoxA@16 = MessageBoxA        ENDIF ;-------------------------------------------- ; Data segment _DATA SEGMENT        TXT   DB 'DLL error', 0        MS    DB 'Message', 0        LIBR  DB 'DLL2.DLL', 0        HLIB  DD ?        MS1   DB 'Message from the library', 0        TEXT  DB 'The string is contained in the main module', 0 IFDEF MASM        NAMEPROC DB ' DLLP1@0', 0 ELSE        NAMEPROC DB 'DLLP1', 0 ENDIF _DATA ENDS ; Code segment _TEXT SEGMENT ; [EBP+10H]   ; Reserved parameter ; [EBP+0CH]   ; Cause of the call ; [EBP+8]     ; DLL module identifier START: ; Load the library        PUSH   OFFSET LIBR        CALL   LoadLibraryA@4        CMP    EAX, 0        JE     _ERR        MOV    HLIB, EAX ; Get the address        PUSH   OFFSET NAMEPROC        PUSH   HLIB        CALL   GetProcAddress@8        CMP    EAX, 0        JNE    YES_NAME ; Error message _ERR:         PUSH   0         PUSH   OFFSET MS         PUSH   OFFSET TXT         PUSH   0         CALL   MessageBoxA@16         JMP    _EXIT YES NAME:         PUSH   OFFSET MS1         PUSH   OFFSET TEXT         CALL   EAX         PUSH   0         PUSH   OFFSET MS         PUSH   EAX         PUSH   0         CALL   MessageBoxA@16 ; Close the library         PUSH   HLIB         CALL   FreeLibrary@4 ; The library is automatically closed ; when exiting the program ; Exit _EXIT:        PUSH    0        CALL    ExitProcess@4 _TEXT ENDS END START 

 

To translate this program, issue the following commands for MASM32:

 ml /c /coff /DMASM dllex2.asm     link /subsystem:windows dllex2.obj 

Issue the following commands for TASM32:

 tasm32 /ml dllex2.asm     tlink32 -aa -Tpd dllex2.obj 

Next, consider an interesting example (Listing 16.5). The primary process uses the resources of the DLL that it has loaded. I have already mentioned that font files are DLLs. It's convenient , isn't it? The resources can be placed into a DLL, separate from the code, and then can be loaded as needed. The program in Listing 16.5 first loads an icon from the DLL resources and sets it as the window icon. If you right-click the mouse somewhere in the window area, a procedure from the DLL will be called. This procedure will alternately set different icons to the window.

Listing 16.5: Loading resources from the dynamic link library

 // The DLL3.RC file // Identifiers #define IDI_ICON1 3 #define IDI ICON2 10 // Define icons IDI_ICON1 ICON "icol.ico" IDI_ICON2 ICON "ico2.ico" ; The DLL3.ASM file .586P PUBLIC SETIC ; Flat memory model IFDEF MASM  .MODEL FLAT, stdcall ELSE  .MODEL FLAT ENDIF ; Constants WM_SETICON    equ 80h IFDEF MASM ; MASM ; Prototypes of external procedures        EXTERN       LoadIconA@8:NEAR        EXTERN       PostMessageA@16:NEAR ; INCLUDELIB directives for the linker        includelib c:\masm32\lib\user32.lib        includelib c: \masm32\lib\kernel32.lib ELSE ; TASM ; Prototypes of external procedures        EXTERN      LoadIconA:NEAR        EXTERN      PostMessageA:NEAR ; INCLUDELIB directives for the linker        includelib c:\tasm32\lib\import32.lib        LoadIconA@8 = LoadIconA        PostMessageA@16 = PostMessageA ENDIF ;--------------------------------------------- ; Data segment _DATA SEGMENT         PRIZ DB 0 _DATA ENDS ; Code segment _TEXT SEGMENT DLLENTRY:        MOV    EAX, 1        RET    12 ; [EBP+8] ; [EBP+0CH] SETIC PROC EXPORT        PUSH   EBP        MOV    EBP, ESP ; Choose the icon to set        CMP    PRIZ, 0        JZ     IC_1        MOV    PRIZ, 0        PUSH   3        JMP    CONT IC_1 :        MOV    PRIZ, 1        PUSH   10 CONT: ; Load the icon from the DLL resources        PUSH   DWORD PTR [EBP+0CH] ; Identifier                                   ; of the DLL        CALL   LoadIconA@8 ; Set the window icon        PUSH   EAX        PUSH   0        PUSH   WM_SETICON        PUSH   DWORD PTR [EBP+08H] ; Window descriptor        CALL   PostMessageA@16        POP    EBP        RET    8 SETIC ENDP _TEXT ENDS END DLLENTRY // The DLLEX3.RC file // Constant definitions #define WS_SYSMENU       0x00080000L #define WS_MINIMIZEBOX   0x00020000L #define WS_MAXIMIZEBOX   0x00010000L #define DS_3DLOOK        0x0004L // Dialog box definition DIAL1 DIALOG 0, 0, 340, 120 STYLE WS_SYSMENU  WS_MINIMIZEBOX  WS_MAXIMIZEBOX  DS_3DLOOK CAPTION "Dialog with an icon from DLL resources" FONT 8, "Arial" { } ; Main module DLLEX3.ASM, calling ; the procedure from the DLL . 586P ; Flat memory model IFDEF MASM  .MODEL FLAT, stdcall ELSE  .MODEL FLAT ENDIF ; Constants ; This message arrives when the window is closed WM_CLOSE        equ 10h WM_INITDIALOG   equ 110h WM_SETICON      equ 80h WM_LBUTTONDOWN  equ 201h ; Prototypes of external procedures IFDEF MASM ; MASM        EXTERN      PostMessageA@16:NEAR        EXTERN      GetProcAddress@8:NEAR        EXTERN      LoadLibraryA@4:NEAR        EXTERN      FreeLibrary@4:NEAR        EXTERN      ExitProcess@4:NEAR        EXTERN      GetModuleHandleA@4:NEAR        EXTERN      DialogBoxParamA@20:NEAR        EXTERN      EndDialog@8:NEAR        EXTERN      LoadIconA@8:NEAR ; INCLUDELIB directives for the linker        includelib c:\masm32\lib\user32.lib        includelib c:\masm32\lib\kernel32.lib ELSE ; INCLUDELIB directives for the linker        includelib c:\tasm32\lib\import32.lib        EXTERN      PostMessageA:NEAR        EXTERN      GetProcAddress:NEAR        EXTERN      LoadLibraryA:NEAR        EXTERN      FreeLibrary:NEAR        EXTERN      ExitProcess:NEAR        EXTERN      GetModuleHandleA:NEAR        EXTERN      DialogBoxParamA:NEAR        EXTERN      EndDialog:NEAR        EXTERN      LoadIconA:NEAR        PostMessageA@16 = PostMessageA        LoadIconA@8 = LoadIconA        EndDialog@8 = EndDialog        GetModuleHandleA@4 = GetModuleHandleA        DialogBoxParamA@20 = DialogBoxParamA        GetProcAddress@8 = GetProcAddress        LoadLibraryA@4 = LoadLibraryA        FreeLibrary@4 = FreeLibrary        ExitProcess@4 = ExitProcess ENDIF ;--------------------------------------------- ; Data segment _DATA SEGMENT        LIBR    DB 'DLL3.DLL', 0        HLIB    DD ?        HINST   DD ?        PA         DB "DIAL1", 0 IFDEF MASM        NAMEPROC   DB "_SETIC@0", 0 ELSE        NAMEPROC   DB "SETIC", 0 ENDIF _DATA ENDS ; Code segment _TEXT SEGMENT START: ; Get the application descriptor        PUSH   0        CALL   GetModuleHandleA@4 ; Create a dialog        MOV    [HINST], EAX        PUSH   0        PUSH   OFFSET WNDPROC        PUSH   0        PUSH   OFFSET PA        PUSH   [HINST]        CALL   DialogBoxParamA@20 ; Exit _EXIT:        PUSH   0        CALL   ExitProcess@4 ; Window procedure ; Position of parameters in the stack ; [BP+014H]  ; LPARAM ; [BP+10H]   ; WAPARAM ; [BP+0CH]   ; MES ; [BP+8]     ; HWND WNDPROC PROC        PUSH  EBP        MOV   EBP, ESP        PUSH  EBX        PUSH  ESI        PUSH  EDI ;--------------        CMP   DWORD PTR [EBP+0CH], WM_CLOSE        JNE   L1 ; Close the library ; The library is closed automatically ; when exiting the program        PUSH  HLIB        CALL  FreeLibrary@4        PUSH  0        PUSH  DWORD PTR [EBP+08H]        CALL  EndDialog@8        JMP   FINISH L1:        CMP   DWORD PTR [EBP+0CH], WM_INITDIALOG        JNE   L2 ; Load the library        PUSH  OFFSET LIBR        CALL  LoadLibraryA@4        MOV   HLIB, EAX ; Load the icon        PUSH  3 ; Program identifier        PUSH  [HLIB] ; Process identifier        CALL  LoadIconA@8 ; Set the icon        PUSH  EAX        PUSH  0 ; Icon type (small)        PUSH  WM_SETICON        PUSH  DWORD PTR [EBP+08H]        CALL  PostMessageA@16        JMP  FINISH L2:        CMP  DWORD PTR [EBP+0CH], WM_LBUTTONDOWN        JNE  FINISH ; Get the address of the DLL procedure        PUSH OFFSET NAMEPROC        PUSH HLIB        CALL GetProcAddress@8 ; Call the procedure with two parameters        PUSH  [HLIB]        PUSH  DWORD PTR [EBP+08H]        CALL  EAX FINISH:        POP   EDI        POP   ESI        POP   EBX        POP   EBP        MOV   EAX, 0        RET   16 WNDPROC   ENDP _TEXT ENDS END START 

 

To translate the program from Listing 16.5, issue the following commands for MASM32:

 ml /c /coff /DMASM dllex3.asm      rc dllex3.rc      link /subsystem:windows dllex3.obj dllex3.res      ml /c /coff /DMASM dll3.asm      rc dll3.rc      link /subsystem:windows /DLL /ENTRY:DLLENTRY dll3.obj dll3.res 

Issue the following commands for TASM32:

 tasm32 /ml dllex3.asm      brcc32 dllex3.rc      tlink32 -aa -Tpd dllex3.obj,,,,,dllex3.res      tasm32 /ml dll3.asm      brcc32 dll3.rc      tlink32 -aa -Tpd dll3.obj,,,,dll3.def,dll3.res 

The contents of the DLL3.DEF file are as follows :

 EXPORTS SETIC 

As you have already noticed, the DLL becomes a part of your program and, with the primary process, can use all its capabilities. Thus, for example, using the GetMessage and PeekMessage functions, it can receive the messages intended for the process. If you need to create a window in the DLL, use the identifier of the program that has called it.