GPF on calling free.

[Prime]

Hi all,

I am writing a multi CPU disassembler, so am trying to abstract out the bits that are common to all target CPUs and just have the CPU specific stuff implemented in decendent classes.

So I have an abstract disassembler class :

Code: Pascal  [Select][+][-]

1.     TCPU    = (tcNone,tc6502, tc65c02, tc65c02wd, tc6512, tc6809);
2.     TCPUSet = SET OF TCPU;
3.  
4.     TOpCode = Class(TObject)
5.       OpStr     : STRING;
6.       OpBytes   : INTEGER;
7.       CPU           : TCPUSet;
8.       Valid         : BOOLEAN;
9.       CONSTRUCTOR Create;
10.     END;
11.  
12.     TADisassembler = Class(TObject)
13.     PROTECTED
14.       FOpCodes  : ARRAY[$00..$FF]OF TOpCode;
15.       FVerbose  : BOOLEAN;
16.       FCPU      : TCPU;
17.  
18.       FUNCTION CalcRelative8(RelOffset     : BYTE) : WORD;
19.       FUNCTION CalcRelative16(RelOffset     : WORD) : WORD;
20.       PROCEDURE DecodeInstruction;   virtual; abstract;
21.       PROCEDURE InitOpcodes;         virtual; abstract;
22.       PROCEDURE SetVerbose(NewValue     : BOOLEAN);
23.     PUBLIC
24.       SymbolList                : TSymbolList;
25.       EntryPoints               : TSymbolList;
26.       Memory                    : TCPUmemory;
27.       MemoryList                : TMemoryList;
28.       PROPERTY Verbose  : BOOLEAN READ FVerbose WRITE SetVerbose;
29.       PROPERTY CPU      : TCPU READ FCPU WRITE FCPU;
30.  
31.       CONSTRUCTOR Create;
32.       DESTRUCTOR Destroy; override;
33.       PROCEDURE Go; virtual; abstract;
34.       PROCEDURE LoadFromFile(FileName   : STRING;
35.                                    PBaseAddr    : DWORD);
36.       PROCEDURE SetCPU(CPUType     : INTEGER);
37.     END;
38.  

Then my CPU specific stuff overrides / inherits. :

Code: Pascal  [Select][+][-]

1.    
2.     TBranch = (brNone,brRelative,brAbsolute,brRtsRti,brZPRelative);
3.  
4.  
5.     TOpCode6502 = Class(TOpCode)
6.       OpStr     : STRING;
7.       OpBytes   : INTEGER;
8.       CPU           : TCPUSet;
9.       Branch    : TBranch;
10.       Valid         : BOOLEAN;
11.     END;
12.  
13.     TDisassembler6502 = Class(TADisassembler)
14.     PROTECTED
15.       PROCEDURE DecodeInstruction;  override;
16.           PROCEDURE InitOpcodes;        override;
17.           PROCEDURE MakeOpCode(OpNo             : INTEGER;
18.                                InOpStr      : STRING;
19.                                        InOpBytes        : INTEGER;
20.                                        InCPU        : TCPUSet;
21.                                        InBranch     : TBranch = brNone);
22.     PUBLIC
23.       CONSTRUCTOR Create;
24.       DESTRUCTOR Destroy; override;
25.       PROCEDURE Go;  override;
26.     END;
27.  

These are in seperate unit files. I have also written code for the virtual methods in TDisassembler6502.
When run the units appear to work however when The free method of TDisassembler6502 is called the program causes a GPF.

In my main program the disassembler is defined as :

Code: Pascal  [Select][+][-]

1. VAR Disassember     : TDisassembler6502;    
2.  

It is createed in my initaliasation procedure with :

Code: Pascal  [Select][+][-]

1.   Disassember:=TDisassembler6502.Create;
2.  

I attempt to free it with :

Code: Pascal  [Select][+][-]

1.   Disassember.Free;
2.  

This is where I get the GPF.

Any idea what the problem might be? If I single step the debugger doesn't even make it to the Destroy methods of either of the classes.

I can post the entire code of the units if wanted just trying to not flood the forum

Cheers.

Phill.

[marcov]

• the disassembler variable is overwritten/corrupted
• the class has already been destroyed
• something in the destructor of the tadisassembler class causes an exception/li]
  

[howardpc]

If Marco's hints are not sufficient to help you trace the error you'll need to share compilable code (or at least a compilable cut-down version) that shows the problem. The devil is in the detail, not in the overall design.

[totya]

Hi, in Lazarus: Project/publish project, then zip this result dir, and attach this zip file to your post.

It is createed in my initaliasation procedure with :

Code: Pascal  [Select][+][-]

1.   Disassember:= TDisassembler6502.Create;

Code: Pascal  [Select][+][-]

1.   Disassember.Free;

Try change for it:

Code: Pascal  [Select][+][-]

1.   Disassember:= nil;
2.   Disassember:= TDisassembler6502.Create;

Code: Pascal  [Select][+][-]

1.   if Assigned(Disassember)
2.     then FreeAndNil(Disassember)
3.     else ShowMessage('variable is nil');

[Prime]

Bingo! I found the problem.

I was calling MemoryList.free in both TADissasembler and it's decendent class, needless to say the second call caused the problem

Thanks for the quick replies.

Cheers.

Phill.