Is it a compiler bug??

You're casting an unititialised integer to a pointer then dereferencing it. The compiler is under no obligation to produce code that does anything useful or sensible in that type of situation.

Stefan

Which C51-Compiler version do you use ?
I think, the code is not correct, but I am not sure !

Mike

C51 V7.01
Here are my source codes (Compile O.K.)...

void CopyRomData (U8 xdata *Des,U8 Index)
{
    U8 code *pbSrc;
    unsigned int Begin;
    SysSetRomPage(ROM_PAGE1);
    Begin=(unsigned int)&((BankH1 CODE *)0)->OffsetData[Index];
    Begin=*(U16 CODE *)Begin;
    pbSrc=(U8 CODE *)Begin;
    do {
        *Des=*pbSrc;
        ++pbSrc;
        ++Des;
    } while(*pbSrc);
    *Des=0;
    SysSetRomPage(ROM_PAGE0);
    //Index=(U8)Begin;//Unmask this line will solve the error.
}

             ; FUNCTION _CopyRomData (BEGIN)
                                           ; SOURCE LINE # 152
0000 8E00        R     MOV     Des,R6
0002 8F00        R     MOV     Des+01H,R7
0004 8D00        R     MOV     Index,R5
                                           ; SOURCE LINE # 153
                                           ; SOURCE LINE # 156
0006 7F10              MOV     R7,#010H
0008 120000      E     LCALL   _SysSetRomPage
                                           ; SOURCE LINE # 157
000B E500        R     MOV     A,Index
000D 75F002            MOV     B,#02H
0010 A4                MUL     AB
0011 2438              ADD     A,#038H
0013 FF                MOV     R7,A
0014 E4                CLR     A
0015 35F0              ADDC    A,B
;---- Variable 'Begin' assigned to Register 'DPTR' ----
0017 8F82              MOV     DPL,R7
0019 F583              MOV     DPH,A
                                           ; SOURCE LINE # 159
001B E4                CLR     A
001C 93                MOVC    A,@A+DPTR
001D F583              MOV     DPH,A  'pbSrc' assigned to Register 'R6/R7' ----
0027         ?C0035:
                                           ; SOURCE LINE # 163
                                           ; SOURCE LINE # 164
0027 8F82              MOV     DPL,R7
0029 8E83              MOV     DPH,R6
002B E4                CLR     A
002C 93                MOVC    A,@A+DPTR
002D 850082      R     MOV     DPL,Des+01H
0030 850083      R     MOV     DPH,Des
0033 F0                MOVX    @DPTR,A
                                           ; SOURCE LINE # 165
0034 0F                INC     R7
0035 BF0001            CJNE    R7,#00H,?C0053
0038 0E                INC     R6
0039         ?C0053:
                                           ; SOURCE LINE # 166
0039 0500        R     INC     Des+01H
003B E500        R     MOV     A,Des+01H
003D 7002              JNZ     ?C0054
003F 0500        R     INC     Des
0041         ?C0054:
                                           ; SOURCE LINE # 167
0041 8F82              MOV     DPL,R7
0043 8E83              MOV     DPH,R6
0045 E4                CLR     A
0046 93                MOVC    A,@A+DPTR
0047 70DE              JNZ     ?C0035
                                           ; SOURCE LINE # 168
0049 850082      R     MOV     DPL,Des+01H
004C 850083      R     MOV     DPH,Des
004F F0                MOVX    @DPTR,A
                                           ; SOURCE LINE # 169
0050 FF                MOV     R7,A
0051 020000      E     LJMP    _SysSetRomPage
             ; FUNCTION _CopyRomData (END)

Looks like a code generator bug to me. "Begin" lives in the DPTR; it takes two MOVCs to fetch a new value; and the first MOVC goes (almost) straight into the DPTR, altering it before the MOVC of the second byte. The address used for the second MOVC is not the same as the address used for the first MOVC.

It may be that the optimizer thinks it's okay to trash the value of Begin because it will no longer be used. That would explain why uncommented the later statement fixes the problem. The compiler would preserve the value of Begin for the later use.

You don't need to assign Begin back to itself anyway; it's just a temporary. How about just:

pbSrc = (U8 CODE *)
    *(U16 CODE *)(&((BankH1 CODE *)0)->OffsetData[Index]);

perhaps it would help if you could just state in words what you're actually trying to do?

What are the U8 and U16 types?

Also, why not try this with the latest C51 release? There have been 9 releases since 7.01.

Jon

Thanks a lot for all your kindly reply!

I know my code looks weird, such as

Begin=*(U16 CODE *)Begin;//U16 means unsigned short

void CopyRomData (U8 XDATA *Des,U8 Index)
{
    U8 CODE *pbSrc;
    unsigned int Begin;//Keil 2B, Win32 4B.
    SysSetRomPage(ROM_PAGE1);//Change Bank, it means the following "MOVC" will retrieve data from specify bank.
    Begin=(unsigned int)&((BankH1 CODE *)0)->OffsetData[Index];//Data offsets are located on begginning of each bank.
    WinWork(winGetRomAddr(&Begin));//For simulator.
    Begin=*(U16 CODE *)Begin;
    WinWork(Begin=U16X(Begin));//Hi-Lo exchange, little-Endian for PC.
    WinWork(winGetRomAddr(&Begin));//For simulator.
    pbSrc=(U8 CODE *)Begin;//Both Target and PC could get the right address.
    strcpy(Des,pbSrc);//I just want to copy string, but keil's library seems refer to 'MOVC' internal(It will access to wrong bank), That's why I wrote a loop myself(see pre post).
    SysSetRomPage(ROM_PAGE0);
}

My CA51-v7.0 product is out of date (1 year/Bought on Sep2002). Can I still download the most update version?

You should be able to download 7.07 or 7.07a.

Jon

Jon,
Thank you!
Kenny