[fpc-devel] According to Valgrind, something is wrong in IndexByte

[Micha Nelissen]

Hi,

In TDbf I use MemScan, which is defined as such: (FPC_DISABLE for testing, normally FPC)

<code>
{$ifdef FPC_DISABLE}

function MemScan(const Buffer: Pointer; Chr: Byte; Length: Integer): Pointer;
var
  I: Integer;
begin
  I := System.IndexByte(Buffer, Length, Chr);
  if I = -1 then
    Result := nil
  else
    Result := Buffer+I;
end;

{$else}

function MemScan(const Buffer: Pointer; Chr: Byte; Length: Integer): Pointer;
asm     
        PUSH    EDI
        MOV     EDI,Buffer
        MOV     AL, Chr
        MOV     ECX,Length
        REPNE   SCASB
        MOV     EAX,0
        JNE     @@1
        MOV     EAX,EDI
        DEC     EAX
@@1:    POP     EDI
end;

{$endif}
</code>

So you see, it's IndexByte with a tweak. If I'm using the FPC version, implemented using IndexByte Valgrind reports a lot of errors like so:

==13664== 44439 errors in context 34 of 34:
==13664== Conditional jump or move depends on uninitialised value(s)
==13664==    at 0x80537C9: SYSTEM_INDEXBYTE$formal$LONGINT$BYTE$$LONGINT (i386.inc:312)
==13664==    by 0x81C3B28: DBF_COMMON_MEMSCAN$POINTER$BYTE$LONGINT$$POINTER (dbf_common.pas:433)
==13664==    by 0x81E51C2: DBF_MEMO_TMEMOFILE_$__READMEMO$LONGINT$TSTREAM (dbf_memo.pas:278)
==13664==    by 0x81C6763: DBF_DBFFILE_TDBFFILE_$__RESTRUCTURETABLE$TDBFFIELDDEFS$BOOLEAN (dbf_dbffile.pas:1303)
==13664==    by 0x81AD8B4: DBF_TDBF_$__PACKTABLE (dbf.pas:1521)

But if I use my own version (which I use for delphi and is i386 specific), it reports no errors in this location, for Dbf_Common/Dbf_Memo.

i386 IndexByte seems way more complex than my custom MemScan, but maybe that's necessary somehow.

Micha