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program Hello;
{$ifdef fpc}
{$mode delphi}
{$endif}
{$APPTYPE CONSOLE}
{$O-}
const
val_O0 = 35;
val_O1 = 74;
val_O2 = 123;
{$ifdef CPUI8086}
const
offset_size = 4;
type
Int = smallint;
UInt = word;
{$else}
const
offset_size = 2*sizeof(pointer);
type
Int = ptrint;
UInt = ptruint;
{$endif}
type
ptr = pointer;
{$ifdef fpc}
codeptr = codepointer;
{$else}
codeptr = pointer;
{$endif}
pPtr = ^ptr;
Bool = Boolean;
// Object woth VMT at offset 0.
TObj0 =
object
Constructor Init;
Function Value(p: UInt): UInt; Virtual;
enD;
// Object with VMT at offset 0, and size = 5.
TObj1 =
object (TObj0)
f1: Byte; // UInt;
Constructor Init;
Function Value(p: UInt): UInt; Virtual;
enD;
// Object with VMT at offset 0, but size = 8. (???)
TObj2 =
object
f1{, f2, f3, f4}: Byte; // UInt;
Constructor Init;
Function Value(p: UInt): UInt; Virtual;
enD;
{ Implmentation }
Constructor TObj0.Init;
begin
enD;
Function TObj0.Value(p: UInt): UInt;
begin
Result := val_O0;
enD;
Constructor TObj1.Init;
begin
enD;
Function TObj1.Value(p: UInt): UInt;
begin
Result := val_O1;
enD;
Constructor TObj2.Init;
begin
enD;
Function TObj2.Value(p: UInt): UInt;
begin
Result := val_O2;
enD;
{ Low Level VMT Routines }
type
pObjVMT = ^TObjVMT;
ppObjVMT = ^pObjVMT;
TObjVMT =
record
fInstanceSize: UInt;
fInstanceSize2: Int;
fParent: ppObjVMT;
enD;
Function GetInstanceSize(AVMT: pObjVMT): UInt;
begin
Result := AVMT.fInstanceSize;
enD;
Function GetVMTPtrOffset(AVMT: pObjVMT): UInt;
begin
writeln('AVMT is ',hexstr(seg(AVMT^),4),':',hexstr(ofs(AVMT^),offset_size));
writeln('AVMT^.fParent is ',hexstr(seg(AVMT^.fParent^),4),':',hexstr(ofs(AVMT^.fParent^),offset_size));
if (AVMT.fParent = nil) then
Result := GetInstanceSize(AVMT) - SizeOf(ptr) else
Result := GetVMTPtrOffset(AVMT.fParent^);
writeln('GetVMTPtrOffset=',hexstr(Result,2*sizeof(UInt)));
enD;
Function SetVMT(Obj: ptr; AVMT: ptr): Bool;
var
p : pptr;
begin
Result := (AVMT <> nil);
if (Result) then
begin
writeln('Obj is ',hexstr(seg(Obj^),4),':',hexstr(ofs(Obj^),offset_size));
p:=pPtr(ptr(Obj) + GetVMTPtrOffset(AVMT));
writeln('Setting p ',hexstr(seg(p^),4),':',hexstr(ofs(p^),offset_size),' to ',hexstr(seg(AVMT^),4),':',hexstr(ofs(AVMT^),offset_size));
p^ := AVMT;
end;
enD;
{ Main }
var
O0: TObj0;
O1: TObj1;
O2: TObj2;
s0, s1, s2: UInt;
v0, v1, v2: ptr;
cn0, cn1, cn2: codeptr;
st : string;
begin
// VMT Pointers
v0 := TypeOf(TObj0);
v1 := TypeOf(TObj1);
v2 := TypeOf(TObj2);
writeln('TObj0 VMT ',hexstr(seg(v0^),4),':',hexstr(ofs(v0^),offset_size));
writeln('TObj1 VMT ',hexstr(seg(v1^),4),':',hexstr(ofs(v1^),offset_size));
writeln('TObj2 VMT ',hexstr(seg(v2^),4),':',hexstr(ofs(v2^),offset_size));
// Object sizes
s0 := SizeOf(TObj0); // = 4
s1 := SizeOf(TObj1); // = 5
s2 := SizeOf(TObj2); // = 8 (???)
writeln(s0);
writeln(s1);
writeln(s2);
// Method pointers
cn0 := @TObj0.Value;
cn1 := @TObj1.Value;
cn2 := @TObj2.Value;
// VMT offsets (use in watches - need in program!)
// Int(@o0._vptr$) - Int(@o0) = 0
// Int(@o1._vptr$) - Int(@o1) = 0
// Int(@o2._vptr$) - Int(@o2) = 1 (???)
{
// Constructors - skipping
O0.Init;
O1.Init;
O2.Init;
}
writeln('@TObj0.Value ',hexstr(seg(cn0^),4),':',hexstr(ofs(cn0^),offset_size));
writeln('@TObj1.Value ',hexstr(seg(cn1^),4),':',hexstr(ofs(cn1^),offset_size));
writeln('@TObj2.Value ',hexstr(seg(cn2^),4),':',hexstr(ofs(cn2^),offset_size));
// Store VMT (emulate constructor)
SetVMT(@O0, TypeOf(TObj0));
SetVMT(@O1, TypeOf(TObj1));
SetVMT(@O2, TypeOf(TObj2));
// readln(st);
st:='c';
if st='c' then
begin
writeln('O0 value is ',O0.VAlue(0),' after O0');
writeln('O1 value is ',O1.VAlue(0),' after O1');
writeln('O2 value is ',O2.VAlue(0),' after O2');
// Call Virtual Functions
O2.f1 := O0.Value(0);
if O2.f1<>val_O0 then
halt(1);
O2.f1 := O1.Value(0);
if O2.f1<>val_O1 then
halt(2);
O2.f1 := O2.Value(0); {CRASHES !!!}
if O2.f1<>val_O2 then
halt(3);
{ SizeOf(TObj2) must be 5,
or ptr(Int(@o2._vptr$) - Int(@o2)) must be 4! }
// MessageBox will be displayed, if all was successfull
end;
writeln(O2.f1, 'Hello, FPC uWorld!', 'Hello', 0);
end.
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