------------------------------------------------------------------------------
                      [ENHANCED] VFP 9.0 FIX - CATCH THE MEMORY ACCESS VIOLATION EXCEPTION
                                   May 2022
                 ------------------------------------------------------------------------------
                                     CCB



1. BUG:

     If we enable catching the memory access violation exception in Visual FoxPro Advanced,
     when Visual FoxPro causes the memory access violation exception (exception code 0xC0000005),
     it will display the exception dialog box twice, 
     and then it will display a dialog box "Are you sure you want to exit Visual FoxPro?",
     if we select "Yes", it will exit Visual FoxPro,
     if we select "No", it will cause the error "There is not enough memory to complete this operation (Error 43)",
     and then it will return to Visual FoxPro, now we can do some important work, and then exit Visual FoxPro.
     It is the startup default for Visual FoxPro Advanced Interactive Development Environment (IDE).

     Please refer to the picture testcatchexception.png:

     If we disable catching the memory access violation exception in Visual FoxPro Advanced,
     when Visual FoxPro causes the memory access violation exception (exception code 0xC0000005),
     it will display the exception dialog box twice, and then exit Visual FoxPro.
     It is the startup default for Visual FoxPro Advanced Runtime and Visual FoxPro Advanced Multi-threaded Runtime.


2. CAUSE:

     There are some BUGs in the following code.


3. RESOLUTION:

     We can write some code to fix the BUG.

     Fun61ca6d :: ; proc near
             pushd 01Ch                                                      ;0x0061ca6d :        6a1c
             pushd offset Data92b680                                                  ;0x0061ca6f :        6880b69200
             call Fun42c14f                                                  ;0x0061ca74 :        e8d6f6e0ff
             mov  eax , dword ptr [ ebp + 8 ]                                ;0x0061ca79 :        8b4508
             xor edi , edi                                                   ;0x0061ca7c :        33ff
             mov  dword ptr [ ebp - 28 ] , edi                               ;0x0061ca7e :        897de4
             cmp  dword ptr [ ebp + 12 ] , 0C00000FDh                        ;0x0061ca81 :        817d0cfd0000c0
             jne Label61caa3                                                 ;0x0061ca88 :        7519
             mov  eax , dword ptr [ eax + 4 ]                                ;0x0061ca8a :        8b4004
             mov  dword ptr [ eax + 0B8h ] , offset Label61ca63                        ;0x0061ca8d :        c780b800000063ca6100
             call  _resetstkoflw                               ;0x0061ca97 :        ff15f4799100
             or  dword ptr [ ebp - 28 ] , 0FFFFFFFFh                         ;0x0061ca9d :        834de4ff
             jmp Label61cb1c                                                 ;0x0061caa1 :        eb79

     Label61caa3 ::
             cmp  dword ptr [ ebp + 16 ] , edi                               ;0x0061caa3 :        397d10
             je Label61cb1c                                                  ;0x0061caa6 :        7474
             push eax                                                        ;0x0061caa8 :        50
             push edi                                                        ;0x0061caa9 :        57
             pushd offset Data9259b4                                                  ;0x0061caaa :        68b4599200
             call Fun61ca47                                                  ;0x0061caaf :        e893ffffff
             mov  dword ptr [ ebp - 36 ] , eax                               ;0x0061cab4 :        8945dc
             cmp eax , 01h                                                   ;0x0061cab7 :        83f801
             je Label61cb0f                                                  ;0x0061caba :        7453
             mov  dword ptr [ ebp - 4 ] , edi                                ;0x0061cabc :        897dfc
             call Fun5531c3                                                  ;0x0061cabf :        e8ff66f3ff
             push  dword ptr [ ebp + 12 ]                                    ;0x0061cac4 :        ff750c
             call Fun846807                                                  ;0x0061cac7 :        e83b9d2200
             mov esi , eax                                                   ;0x0061cacc :        8bf0
             mov  dword ptr [ ebp - 40 ] , esi                               ;0x0061cace :        8975d8
             cmp esi , edi                                                   ;0x0061cad1 :        3bf7
             je Label61cb0b                                                  ;0x0061cad3 :        7436
             mov ecx , 0910h                                                 ;0x0061cad5 :        b910090000
             call Fun42c583                                                  ;0x0061cada :        e8a4fae0ff
             mov  dword ptr [ ebp - 32 ] , eax                               ;0x0061cadf :        8945e0
             pushd 01h                                                       ;0x0061cae2 :        6a01
             call Fun7bddae                                                  ;0x0061cae4 :        e8c5121a00
             mov  eax , dword ptr [esi]                                      ;0x0061cae9 :        8b06
             mov  dword ptr [ ebp - 44 ] , eax                               ;0x0061caeb :        8945d4
             pushd 010h                                                      ;0x0061caee :        6a10
             push  dword ptr [ ebp - 32 ]                                    ;0x0061caf0 :        ff75e0
             push eax                                                        ;0x0061caf3 :        50
             push edi                                                        ;0x0061caf4 :        57
             call  MessageBoxA                                 ;0x0061caf5 :        ff15d4729100
             mov ecx , esi                                                   ;0x0061cafb :        8bce
             call Fun42c1e2                                                  ;0x0061cafd :        e8e0f6e0ff


     ;
     ;                 -------------------------------------------------------------------
     ;                      VFP 9.0 FIX - CATCH THE MEMORY ACCESS VIOLATION EXCEPTION
     ;                                   May 2022
     ;                 -------------------------------------------------------------------
     ;                                     CCB
     ;
     ; Catch the memory access violation exception (exception code 0xC0000005).
     ;
     ; 2022/5/13, by ccb
     ;

             cmp dword ptr vfpa_sys9100_data,00h
             je Label61cb02
             cmp  dword ptr [ ebp + 12 ] , 0C0000005h
             jne Label61cb02
             pushd 00h
             pushd 02h
             pushd 00h
             pushd 00h
             lea eax ,  byte ptr vfpa_sys9100_text
             push eax
             call Fun6da248
             cmp eax , 02h
             jne Label61cb02
             mov  eax , dword ptr [ ebp + 8 ]
             mov  eax , dword ptr [ eax + 4 ]
             mov  dword ptr [ eax + 0B8h ] , offset Label61cb01
             call  _resetstkoflw
             or  dword ptr [ ebp - 28 ] , 0FFFFFFFFh
             jmp Label61cb1c
     Label61cb01 ::
             mov ecx , 0B6h
             jmp Fun544742


     Label61cb02 ::
             jmp Label61cb0b                                                 ;0x0061cb02 :        eb07

     Label61cb0b ::
             or  dword ptr [ ebp - 4 ] , 0FFFFFFFFh                          ;0x0061cb0b :        834dfcff

     Label61cb0f ::
             cmp  dword ptr [ ebp - 36 ] , 02h                               ;0x0061cb0f :        837ddc02
             jne Label61cb1c                                                 ;0x0061cb13 :        7507
             mov  dword ptr [ ebp - 28 ] , 01h                               ;0x0061cb15 :        c745e401000000

     Label61cb1c ::
             mov  eax , dword ptr [ ebp - 28 ]                               ;0x0061cb1c :        8b45e4
             call Fun42c18a                                                  ;0x0061cb1f :        e866f6e0ff
             ret 0Ch                                                         ;0x0061cb24 :        c20c00


4. APPLIES TO:

     VFP 6.0.8167.0
     VFP 6.0.8961.0 (SP5)

     VFP 7.0.0.9262
     VFP 7.0.0.9465 (SP1)

     VFP 8.0.0.2521
     VFP 8.0.0.3117 (SP1)

     VFP 9.0.0.2412
     VFP 9.0.0.3504 (SP1)
     VFP 9.0.0.4611 (SP2)
     VFP 9.0.0.5015 (SP2)
     VFP 9.0.0.5411 (SP2)
     VFP 9.0.0.5721 (SP2)
     VFP 9.0.0.5815 (SP2)
     VFP 9.0.0.6303 (SP2)
     VFP 9.0.0.6602 (SP2)
     VFP 9.0.0.7423 (SP2)

     The bug has been fixed in VFP Advanced.


5. REFERENCE WEBSITES:

     1, baiyujia.com:
     http://www.baiyujia.com
     http://www.baiyujia.com/vfpdocuments/f_vfp9fix212.asp


6. OTHER:

     For reference only, there is no guarantees.

     Any questions or suggestions, please send me an email at ccb2000@163.com.