cannot get hint about class variable from within class method while
debugging
lazarus / 12-Debugger

----------------------------------------------------------------------
kalixo · 2014-06-25 08:10

Hello,

I have been able to reproduce this error on lazarus 1.2.2 and 1.2.4
with 
Free Pascal Compiler version 2.6.4 [2014/04/20] for i386
and
GNU gdb (Ubuntu 7.7-0ubuntu3.1) 7.7
Setting a breakpoint on ' yourage := 5;' I can hover over self.yourage
and get a correct value in the tooltip but not over 'yourage' solo,
when it says 'Type TMYOBJECT = class  has no component named yourage',
but I'm quite sure it has .
It seems like gdb can't infer the scope of the variable when the
'self' is missing. Why is that? I was trying to compile a bigger
legacy project and will not be able to debug it?!

Some hints appreciated... the log file is a start of lazarus with
debug enabled.

Code: [Select]unit Unit1;

{$mode Delphi}

interface

uses
  Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs,
StdCtrls;

type

  { TForm1 }

  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { private declarations }
  public
    { public declarations }
  end;

type
  tvector = array[0..1] of double;

type
  tmyobject = class(TObject)
    yourage: integer;
    thething: array[0..1] of tvector;
  public
    constructor Create();
    procedure doblu();
  end;


var
  Form1: TForm1;

implementation

{$R *.lfm}

{ TForm1 }

procedure TForm1.Button1Click(Sender: TObject);
var
  myobj: tmyobject;
begin
  myobj := tmyobject.Create();
  myobj.yourage := 2;
  myobj.doblu();

end;

procedure tmyobject.doblu();
begin
  self.yourage := 1; //hover over this and it is right
  yourage := 5; //impossible
  thething[1][1] := 3;
end;

constructor tmyobject.Create();
begin
  yourage := 4;
  thething[0][0] := 1;
  thething[0][1] := 2;
end;

end.

----------------------------------------------------------------------
Blaazen · 2014-06-25 09:26

I cannot reproduce, I tried with Linux, Laz. 2.7.1 + GDB 7.5.1 and
Wine, Laz. 1.2.4, FPC 2.6.4 + unknown GDB (its the version that comes
with Laz.).
Note that program break is before line, i.e.:
Code: [Select]    self.yourage := 1; //hover over this and it is right
(!) yourage := 5; //impossiblewill show both yourage or self.yourage =
1.
I've never saw Quote'Type TMYOBJECT = class  has no component named
yourage' with your demo.

----------------------------------------------------------------------
kalixo · 2014-06-25 10:40

I think I have a pretty standard setup. As is documented in the log
attached above,
gdb returns
Code: [Select] << TCmdLineDebugger.ReadLn "^error,msg="Type TMYOBJECT
= class  has no component named yourage.""upon 'ptype yourage'. The
flaw mus be here. Blaazen, as you have tried with an older gdb
version, do you think it is worth installing an old package like
yours?
I have tried on another machine, this tim 64bit, but the same...

Code: [Select]<< Run OnIdle
OnIdle: Finished
Executing (Recurse-Count=0) queued= 0 CmdPrior=999 CmdMinRunLvl=-1 :
"TGDBMIDebuggerCommandEvaluate: Self.yourage" State=Pause
PauseWaitState=0
  >>Enter: TGDBType.ProcessExpression: Expr="Self.yourage",
Flags=[gtcfClassIsPointer, gtcfExprEvaluate, gtcfExprEvalStrFixed,
gtcfAutoCastClass], State=gtpsInitial
  <<Exit:  TGDBType.ProcessExpression: state = gtpsInitialSimple 
Result=False Kind=skSimple Attr= Typename="" InternTpName=""
TypeDeclaration=""
  >> TCmdLineDebugger.SendCmdLn "ptype Self.yourage"
  << TCmdLineDebugger.ReadLn "&"ptype Self.yourage\n""
  << TCmdLineDebugger.ReadLn "&"warning: can't find linker symbol for
virtual table for `<unnamed type>' value\n""
  << TCmdLineDebugger.ReadLn "~"type = LONGINT\n""
  << TCmdLineDebugger.ReadLn "^done"
  << TCmdLineDebugger.ReadLn "(gdb) "
  ParseTypeFromGdb: Flags= Kind=ptprkSimple Name="LONGINT"
  >>Enter: TGDBType.ProcessExpression: Expr="Self.yourage",
Flags=[gtcfClassIsPointer, gtcfExprEvaluate, gtcfExprEvalStrFixed,
gtcfAutoCastClass], State=gtpsInitialSimple
  <<Exit:  TGDBType.ProcessExpression: state = gtpsInitialSimple 
Result=False Kind=skSimple Attr= Typename="" InternTpName=""
TypeDeclaration=""
  >> TCmdLineDebugger.SendCmdLn "whatis Self.yourage"
  << TCmdLineDebugger.ReadLn "&"whatis Self.yourage\n""
  << TCmdLineDebugger.ReadLn "&"warning: can't find linker symbol for
virtual table for `<unnamed type>' value\n""
  << TCmdLineDebugger.ReadLn "~"type = LONGINT\n""
  << TCmdLineDebugger.ReadLn "^done"
  << TCmdLineDebugger.ReadLn "(gdb) "
  ParseTypeFromGdb: Flags= Kind=ptprkSimple Name="LONGINT"
  >>Enter: TGDBType.ProcessExpression: Expr="Self.yourage",
Flags=[gtcfClassIsPointer, gtcfExprEvaluate, gtcfExprEvalStrFixed,
gtcfAutoCastClass], State=gtpsInitialSimple
  <<Exit:  TGDBType.ProcessExpression: state = gtpsEvalExpr 
Result=False Kind=skSimple Attr= Typename="LONGINT"
InternTpName="LONGINT" TypeDeclaration=""
  >> TCmdLineDebugger.SendCmdLn "-data-evaluate-expression
Self.yourage"
  << TCmdLineDebugger.ReadLn "&"warning: can't find linker symbol for
virtual table for `<unnamed type>' value\n""
  << TCmdLineDebugger.ReadLn "^done,value="5""
  << TCmdLineDebugger.ReadLn "(gdb) "
  >>Enter: TGDBType.ProcessExpression: Expr="Self.yourage",
Flags=[gtcfClassIsPointer, gtcfExprEvaluate, gtcfExprEvalStrFixed,
gtcfAutoCastClass], State=gtpsEvalExpr
  <<Exit:  TGDBType.ProcessExpression: state = gtpsFinished 
Result=True Kind=skSimple Attr= Typename="LONGINT"
InternTpName="LONGINT" TypeDeclaration=""
Exec done
Leaving Queue with count: 0 Recurse-Count=0 State=Pause
>> Run OnIdle
  DebugDataMonitor: >>ENTER: TSnapshotManager.DoDebuggerIdle  New-
State=Pause
  DebugDataMonitor: <<EXIT: TSnapshotManager.DoDebuggerIdle
  OnIdle: UnLock
<< Run OnIdle
OnIdle: Finished
Executing (Recurse-Count=0) queued= 0 CmdPrior=999 CmdMinRunLvl=-1 :
"TGDBMIDebuggerCommandEvaluate: yourage" State=Pause PauseWaitState=0
  >>Enter: TGDBType.ProcessExpression: Expr="yourage",
Flags=[gtcfClassIsPointer, gtcfExprEvaluate, gtcfExprEvalStrFixed,
gtcfAutoCastClass], State=gtpsInitial
  <<Exit:  TGDBType.ProcessExpression: state = gtpsInitialSimple 
Result=False Kind=skSimple Attr= Typename="" InternTpName=""
TypeDeclaration=""
  >> TCmdLineDebugger.SendCmdLn "ptype yourage"
  << TCmdLineDebugger.ReadLn "&"ptype yourage\n""
  << TCmdLineDebugger.ReadLn "&"Type TMYOBJECT = class  has no
component named yourage.\n""
  << TCmdLineDebugger.ReadLn "^error,msg="Type TMYOBJECT = class  has
no component named yourage.""
  << TCmdLineDebugger.ReadLn "(gdb) "
  >>Enter: TGDBType.ProcessExpression: Expr="yourage",
Flags=[gtcfClassIsPointer, gtcfExprEvaluate, gtcfExprEvalStrFixed,
gtcfAutoCastClass], State=gtpsInitialSimple
  <<Exit:  TGDBType.ProcessExpression: state = gtpsInitialSimple 
Result=True Kind=skSimple Attr= Typename="" InternTpName=""
TypeDeclaration=""
  >> TCmdLineDebugger.SendCmdLn "-data-evaluate-expression parentfp"
  << TCmdLineDebugger.ReadLn "^error,msg="No symbol \"parentfp\" in
current context.""
  << TCmdLineDebugger.ReadLn "(gdb) "
Exec done

----------------------------------------------------------------------
Blaazen · 2014-06-25 10:51

QuoteThe flaw mus be here. Blaazen, as you have tried with an older
gdb version, do you think it is worth installing an old package like
yours?
Wait for Martin_fr, or send him private message. He is the most
involved with debugger here.

----------------------------------------------------------------------
kalixo · 2014-06-25 11:35

wow. So this seems to be some kind of regression in gdb?
I just built GNU gdb (GDB) 7.5.1  (and others) from source  and it
works fine.

so, my tests as well show:
gdb version
7.7.1 - broken
7.7 - broken
7.6.2 - fine
7.5.1 - fine

So should there be opened a bug? Please advise...

----------------------------------------------------------------------
Martin_fr · 2014-06-25 15:03

It is either gdb, your linker, or fpc dwarf generator.

  >> TCmdLineDebugger.SendCmdLn "ptype Self.yourage"
  << TCmdLineDebugger.ReadLn "&"ptype Self.yourage\n""
  << TCmdLineDebugger.ReadLn "&"warning: can't find linker symbol for
virtual table for `<unnamed type>' value\n""

There is a warning there too.

One thing: some gdb get irritated, if other units use stabs (while you
used dwarf / recommended).

So maybe recompile the LCL (and other ...) with either no debug, or
dwarf. (afaik it has stabs by default)

---
If you look at the "Locals" does it show

this
$this
self
$self

?

EDIT:
Actually found in the log "this"

which afaik is ok...

----------------------------------------------------------------------
kalixo · 2014-06-25 15:21

the warning also appears with the gdb 7.6.2 version, which works fine

Code: [Select]  >> TCmdLineDebugger.SendCmdLn "-data-evaluate-
expression yourage"
  << TCmdLineDebugger.ReadLn "&"warning: can't find linker symbol for
virtual table for `<unnamed type>' value\n""
  << TCmdLineDebugger.ReadLn "^done,value="5""
  << TCmdLineDebugger.ReadLn "(gdb) "
  >>Enter: TGDBType.ProcessExpression: Expr="yourage",
Flags=[gtcfClassIsPointer, gtcfExprEvaluate, gtcfExprEvalStrFixed,
gtcfAutoCastClass], State=gtpsEvalExpr
I recompiled the ide in profile 'normal', nothing. As for production
use, I might stick to 7.6.2, but if I can do something to help nail
down the bug, feel free to ask.