On Aug 12, 2005, at 05:04, Micha Nelissen wrote:
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
Have you investigated more into the Valgrind behavior?
The jump (JNE @@1) is reacting to "REPNE SCASB" and all values seem
to be defined.
Valgrind may be expecting some numerical operation to set the flags.
"Flags Affected: None; however, the CMPS and SCAS instructions do set
the status flags in the EFLAGS register."
Intel: "IA-32 Intel Architecture Software Developer’s Manual"
IA-32-2b.pdf
Jan
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