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Archive for the ‘Conference Topics’ Category

The magic Delphi ReturnAddress intrinsic

Posted by jpluimers on 2020/02/05

I could not find any official place where ReturnAddress is documented even though it is used at quite a few places in the RTL, VCL, FMX and 3rd party libraries like DUnitX, Spring4D, JCL, ReportBuilder, TeeChart.

I tried searching it in the contexts of Delphi 2007, Delphi 2009, but there is only a [Archive.is] different System.ObjAuto.TParameters.ReturnAddress documented in XE2 and higher.

procedure Abort;
begin
  raise EAbort.CreateRes(@SOperationAborted) at ReturnAddress;
end;

There is a (usually broken*) ReturnAddr function used in various places of the RTL/VCL/FMX and (therefore wrongfully copied) in many other peoples code.

  function ReturnAddr: Pointer;
  // From classes.pas
  asm
    MOV     EAX,[EBP+4] // sysutils.pas says [EBP-4], but this works !
  end;

See the above link; I think this was fixed in Delphi XE, but the issue is still open.

Related to the above is the documented ExceptAddr.

I’ve used this in my ExceptionHelperUnit to build a GetStackTrace function in the example gist below.

I found these posts documenting the behaviour of the above intrinsic functions and more:

–jeroen

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Posted in Conference Topics, Conferences, Delphi, Development, Event, Software Development | Leave a Comment »

Dependencies

Posted by jpluimers on 2020/01/28

Last week in Delphi developer switching to C# – Stack Overflow « The Wiert Corner – irregular stream of stuff I wrote about having a broad toolset.

Having such a toolset however does not mean you should stuff your project with dependencies. Choosing a limited set of tools is a very important part of building solid projects.

It does not mean you should avoid dependencies, just that you need to be aware on them and how they add up.

To get a feel for that, the comics on the right and below.

Sources:

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Delphi, compiler intrinsics and generic type matching

Posted by jpluimers on 2020/01/21

For my link archive in case I ever need to do Delphi generic type matching on intrinsic types. This will be tricky as you can have typed types like [WayBack] type TDate = type TDateTime since the early Delphi ages.

[WayBack] Hi, by using compiler intrinsics, is it possible to check if a generic type parameter is an unsigned integer? – Malcon X Portela – Google+

It will probably come down to fast intrinsic type mapping and slower typed type mapping.

The above WayBack link contains the most important bits of the Google+ post:

Malcon X Portela, Delphi Developers, 2 Jan 2018
Hi, by using compiler intrinsics, is it possible to check if a generic type parameter is an unsigned integer? I have the following code:
function TChecker<T>.CheckIsUnsigned: Boolean;
begin
  if GetTypeKind(T) = tkInteger then
  begin
  if SizeOf(T) = 4 then
  begin
    // TODO: Check if it is an unsigned 32-bit integer
    Result := True;
  end else if SizeOf(T) = 2 then
  begin
    // TODO: Check if it is an unsigned 16-bit integer
    Result := True;
  end else
  begin
    // TODO: Check if it is an unsigned 8-bit integer
    Result := True;
  end;
  end else
  begin
    Result := False;
  end;
end;
The code should return True only if the ‘T’ generic type parameter is an unsigned integer. I remember that +Stefan Glienke posted here some code that can do this trick, however, I am not able to find that now.

Thanks!

Malcon X Portela+1
Hi +Jeroen Wiert Pluimers, my answer can be a bit disappointing, sorry :( Some time after writing this question here, I just realized which for the things I was originally trying to do, being signed or unsigned would not change anything on the final result hehehehe :D But from this amazing project https://github.com/d-mozulyov/Rapid.Generics (entire credits goes to Dmitry Mozulyov for the magic), it is possible to write the check to the generic type parameter in order to identify if it is a 32-bit/64-bit signed or unsigned number.
LTypeData := PTypeInfo(TypeInfo(T)).TypeData;

case GetTypeKind(T) of
  tkInteger:
  begin
    {case LTypeData.OrdType of
      otSLong: Writeln('32-bit signed');
      otULong: Writeln('32-bit unsigned');
    end;}
    // the above code does the same thing
    if LTypeData.MaxValue > LTypeData.MinValue then
    begin
      Writeln('32-bit signed');
    end else
    begin
      Writeln('32-bit unsigned');
    end;
  end;
  tkInt64:
  begin
    if LTypeData.MaxInt64Value > LTypeData.MinInt64Value then
    begin
      Writeln('64-bit signed');
    end else
    begin
      Writeln('64-bit unsigned');
    end;
  end;
end;

The [WayBack] Rapid.Generics project is indeed cool, but unmaintained and has no unit tests. The main code is in some [Wayback] 30k lines Rapid.Generics.pas unit with some cool ideas and implementations. Hopefully people will find time to integrate some of the ideas there into basically the only well maintained Delphi generics library Spring4D.

A big limitation might be that the code is Delphi XE8 and up only, whereas Spring4D supports older Delphi versions.

–jeroen

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Delphi: A few notes on tracking down a use-after free related issue involving interfaces crashing inside System._IntfClear.

Posted by jpluimers on 2020/01/20

A few notes on tracking down a use-after free related issue involving interfaces.

The crash message is like this:

Project UseAfterFreeWithInterface.exe raised exception class $C0000005 with message 'access violation at 0x004106c0: read of address 0x80808088'.

Two things here:

the is the hexadecimal value of STATUS_ACCESS_VIOLATION, which is sort of mentioned in [WayBack] Delphi 2009: EExternalException Class, but not documented in any more recent Delphi versions. It is in the code for the units System, System.SysUtils and Winapi.Windows (see below).
The value is not well documented on the Microsoft documentation site either: you sort of have to connect the dots between site:docs.microsoft.com “0xC0000005” – Google Search and [WayBack] site:docs.microsoft.com “STATUS_ACCESS_VIOLATION” – Google Search to find for instance these two:
- [WayBack] Hardware Exceptions | Microsoft Docs
- [WayBack] GetExceptionCode macro – Windows applications | Microsoft Docs
The 0x80808088 comes from the [WayBack] FastMM4.pas DebugFillPattern value $80808080 which is used to overwrite freed memory. Not all versions of FastMM4.pas have that value near the DebugFillPattern in the code, so I raised an issue for that: [WayBack] Document default 32-bit values of `DebugFillPattern` and `DebugReservedAddress` · Issue #67 · pleriche/FastMM4 · GitHub

The relation between $80808088 and $80808080 (a difference of just $00000008) comes clear when you look at the System._IntClear method disassembly below.
If you use EurekaLog instead of FastMM4, then you addresses will be patterns based on $DEADBEEF, see these links on why:
- [WayBack] EurekaLog 7 Documentation: Root > Integral parts > Options > Features page > Memory problems page
- via [WayBack] Read of address DEADBEE7. – Source of this raise? – General Help – Delphi-PRAXiS [en]

An important note first

Basically any memory value in an exception starting with $8080 and sometimes even $80 should raise suspicion: it usually means a use-after-free case.

You see these errors with FastMM and not with the memory manager as [WayBack] delphi • View topic • Problem with FastMM and D7 explains:

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Posted in Conference Topics, Conferences, Delphi, Development, Event, Software Development | 8 Comments »

Python – list transformation; string formatting – Stack Overflow

Posted by jpluimers on 2020/01/08

Sometimes simple examples are the best: [WayBack] Python – list transformation – Stack Overflow.

Interactive example (note you can run and save at repl.it in either [WayBack] Repl.it – Python 3 or [WayBack] Repl.it – Python 2; you can run but not save it at [WayBack] Welcome to Python.org: interactive Python shell):

# Links the documentation are Python 2, though everything works in Python 3 as well.

x = [1,2,3,4,5,11]
print("x: ", repr(x))

y = ['01','02','03','04','05','11']
print("y: ", repr(y))

# List comprehension https://docs.python.org/2/tutorial/datastructures.html#list-comprehensions
# ... using `str.format()` (Python >= 2.6): https://docs.python.org/2/library/stdtypes.html#str.format and https://docs.python.org/2/library/string.html#formatstrings
y = ["{0:0>2}".format(v) for v in x]
print("y: ", repr(y))

# ... using the traditional `%` formatting operator (Python < 2.6): https://docs.python.org/2/library/stdtypes.html#string-formatting y = ["%02d" % v for v in x] print("y: ", repr(y)) # ... using the format()` function (Python >= 2.6): https://docs.python.org/2/library/functions.html#format and https://docs.python.org/2/library/string.html#formatstrings
# this omits the "{0:...}" ceremony from the positional #0 parameter
y = [format(v, "0>2") for v in x]
print("y: ", repr(y))

# Note that for new style format strings, the positional argument (to specify argument #0) is optional (Python >= 2.7) https://docs.python.org/2/library/string.html#formatstrings
y = ["{:0>2}".format(v) for v in x]
print("y: ", repr(y))

# Using `lambda`
# ... Python < 3 return a list y = map(lambda v: "%02d" %v, x) print("y: ", repr(y)) # ... Python >= 3 return a map object to iterate over https://stackoverflow.com/questions/1303347/getting-a-map-to-return-a-list-in-python-3-x/1303354#1303354
y = list(map(lambda v: "%02d" %v, x))
print("y: ", repr(y))

Output:

Python 3	Python 2
Python 3.6.1 (default, Dec 2015, 13:05:11) [GCC 4.8.2] on linux x: [1, 2, 3, 4, 5, 11] y: ['01', '02', '03', '04', '05', '11'] y: ['01', '02', '03', '04', '05', '11'] y: ['01', '02', '03', '04', '05', '11'] y: ['01', '02', '03', '04', '05', '11'] y: ['01', '02', '03', '04', '05', '11'] y: <map object at 0x7fe1218200b8> y: ['01', '02', '03', '04', '05', '11']	Python 2.7.10 (default, Jul 14 2015, 19:46:27) [GCC 4.8.2] on linux ('x: ', '[1, 2, 3, 4, 5, 11]') ('y: ', "['01', '02', '03', '04', '05', '11']") ('y: ', "['01', '02', '03', '04', '05', '11']") ('y: ', "['01', '02', '03', '04', '05', '11']") ('y: ', "['01', '02', '03', '04', '05', '11']") ('y: ', "['01', '02', '03', '04', '05', '11']") ('y: ', "['01', '02', '03', '04', '05', '11']") ('y: ', "['01', '02', '03', '04', '05', '11']")

Python 3

Python 2

Python 3.6.1 (default, Dec 2015, 13:05:11)
[GCC 4.8.2] on linux
   
x:  [1, 2, 3, 4, 5, 11]
y:  ['01', '02', '03', '04', '05', '11']
y:  ['01', '02', '03', '04', '05', '11']
y:  ['01', '02', '03', '04', '05', '11']
y:  ['01', '02', '03', '04', '05', '11']
y:  ['01', '02', '03', '04', '05', '11']
y:  <map object at 0x7fe1218200b8>
y:  ['01', '02', '03', '04', '05', '11']

Python 2.7.10 (default, Jul 14 2015, 19:46:27)
[GCC 4.8.2] on linux
   
('x: ', '[1, 2, 3, 4, 5, 11]')
('y: ', "['01', '02', '03', '04', '05', '11']")
('y: ', "['01', '02', '03', '04', '05', '11']")
('y: ', "['01', '02', '03', '04', '05', '11']")
('y: ', "['01', '02', '03', '04', '05', '11']")
('y: ', "['01', '02', '03', '04', '05', '11']")
('y: ', "['01', '02', '03', '04', '05', '11']")
('y: ', "['01', '02', '03', '04', '05', '11']")

–jeroen

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TFreedObject in FastMM4/FastMM4.pas at master · pleriche/FastMM4 · GitHub

Posted by jpluimers on 2020/01/08

Reminder to Self:

  {The class used to catch attempts to execute a virtual method of a freed
   object}
  TFreedObject = class
  public
    procedure GetVirtualMethodIndex;
    procedure VirtualMethodError;
{$ifdef CatchUseOfFreedInterfaces}
    procedure InterfaceError;
{$endif}
  end;

If you encounter the class TFreedObject when doing a cast, then you’re working on a freed object and have FastMM4 enabled to detect that.

Source: [WayBack] FastMM4/FastMM4.pas at master · pleriche/FastMM4 · GitHub; FastMM4 – A memory manager for Delphi and C++ Builder with powerful debugging facilities

Note that if you want to see the underlying FastMM data for any TObject allocation, use this watch (where Self is the current instance):

PFullDebugBlockHeader(PByte(Self) - SizeOf(TFullDebugBlockHeader))^

You can also put a ,r behind it to see the fields of this structure:

(Reserved1:nil; Reserved2:nil; AllocatedByRoutine:$41BF74; AllocationGroup:0; 
AllocationNumber:592682; 
AllocationStackTrace:(4224198, 4233131, 4235210, 11103806, 6552132, 131126, 6597961, 11106984, 4235210, 11107153, 11104090); 
AllocatedByThread:90428; FreedByThread:90428; 
FreeStackTrace:(4241541, 131126, 4235210, 11103806, 6552132, 131126, 6597961, 11106984, 4235210, 11107153, 11104090); 
UserSize:36; PreviouslyUsedByClass:132272; HeaderCheckSum:2673350594)

–jeroen

Posted in Conference Topics, Conferences, Delphi, Development, Event, Software Development | Leave a Comment »

Using a main check main to call a main function in Python

Posted by jpluimers on 2020/01/01

[WayBack] __main__ — Top-level script environment — Python 3 documentation recommends code like this:

if __name__ == "__main__":
    # execute only if run as a script
    main()

This has many cool possibilities, including these that I like most as a beginning Python developer:

having your def main(): function in a separate source file
allowing to return prematurely from your main function (you cannot do this from the main block)
allowing a file to distinguish if it is being loaded as a module, or as a main program

–jeroen

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Delphi multi-threading: confused by TThread.Synchronize / TThread.Queue? You’re not alone. And you need to be aware of exceptions there too.

Posted by jpluimers on 2020/01/01

Below an elaboration on my answer to the question [WayBack] I don’t understand the following part of the second Delphi example:TThread.Synchronize… – Alberto Paganini – Google+:

I was looking at the Task example at the EMB wiki link below

http://docwiki.embarcadero.com/RADStudio/Tokyo/en/Tutorial:_Using_Tasks_from_the_Parallel_Programming_Library

and I don’t understand the following part of the second Delphi example:
TThread.Synchronize(nil,
  procedure
  begin
    Label1.Text := lValue.ToString;
  end);
why is there the need to pass Label1.Text := lValue.ToString; as procedure in TThread.Synchronize ?

Why not a simple Label1.Text := lValue.ToString; ?

Basically that question can be either of these:

Why is there no easier language construct than wrapping the callback in a procedure (anonymous method).
Why a call to TThread.Synchronize at all?

The tutorial that Alberto refers to is [WayBack ] Tutorial: Using Tasks from the Parallel Programming Library – RAD Studio. That example uses the TTask feature in Delphi, but the portion he has a question about is general to any multi-treading in Delphi that touches the updating of a VCL or FMX UI from another thread.

This is the more complete code in the meant example:

procedure TForm1.ButtonTask1Click(Sender: TObject);
var
  lValue: Integer;
begin
    Label1.Text := '--';
    TTask.Run(procedure
      begin
          {Some calculation that takes time}
          Sleep(3000);
          lValue := Random(10);
          TThread.Synchronize(nil,
            procedure
            begin
                  Label1.Text := lValue.ToString;
            end);
      end);
end;

What happens here is that the TTask is used to run some code (starting with {Some calculation that takes time}) in a different thread (that is being determined by the framework behind TTask).

I recommend against using TTask (or any other part of the Delphi Parallel Programming Library) as I agree with Stefan Glienke in [WayBack] Hello, Do you know why the “default” keyword of a class property is sometime defined also as an attribute ? – Paul TOTH – Google+:

If that works as well as the PPL does I would not touch it with a 10 foot pole ;)

With “that”, he refers to the APL (Asynchronous Programming Library [Archive.is]) which got introduced in Delphi XE8 and adds asynchronous support for UI controls, but unlike .NET (which implements it on the .NET TControl equivalent) shifted it down to TComponent probably because that’s the common ancestor for both VCL and FMX. But that’s a topic for another day.

The Delphi Parallel Programming Library (DPL) is a complex and intricate framework originally started as Delphi Parallel Library (DPL) and modelled after [WayBack] Intel’s Threading Building Blocks (TBB) and Microsoft’s Task Parallel Library (TPL) (not in WayBack, but moved to the CHM file [WayBack], see also[WayBack] Task Parallel Library changes since the MSDN Magazine article | Parallel Programming with .NET)

Most parts of the DPL were written over at least 7 years time by former Chief Scientist Allen Bauer and introduced in Delphi XE7 as the Delphi Parallel Programming Library (PPL), see [WayBack] Delphi Parallel Programming Library & Memory Managers – Steve Maughan and [WayBack] The Oracle at Delphi: Lock my Object… Please!.

Since Delphi XE7, the PPL hardly got maintenance and now most if not all of the people having knowledge about it have left Embarcadero: early 2016, [Archive.is] Delphi Chief Scientist Allen Bauer Has Left Embarcadero/Idera | Hacker News leaving a big gap as “There are no plans that I’m aware of to move someone into my old position… All those that I would consider qualified are either already gone or are currently looking elsewhere.” (it is not in the [WayBack] part of How safe is Delphis future? Who is the new Lead Compiler Engineer? Who is the new Chief Scientist? – Ralf Stocker – Google+, hence the screen shot).

Luckily, Allen copied most of his old Embarcadero blog over to his personal one (including comments!), so there is quite some historic reference, see for instance [WayBack] Thread pools <> Task handling. – Community Blogs – Embarcadero Community and [WayBack] The Oracle at Delphi: Thread pools <> Task handling.

So back ensuring you can execute some code on the main thread and the questions from the G+ post:

Why is there no easier language construct than wrapping the callback in a procedure (anonymous method).
Why a call to TThread.Synchronize at all?

Lets start with the questions in order I answered them, starting with the my response:

Read the rest of this entry »

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Learn so say ‘No’: ‘No’ your way to trust workshop

Posted by jpluimers on 2019/11/29

[WayBack] ‘No’ your way to trust workshop slide deck:

Published on May 17, 2018

We should say ‘no’ far more often than we do. Why we don’t, the consequences, and how to get comfortable with and effective in saying ‘no’ is the subject of this workshop. Beauty is that you don’t even need to say ‘no’ in order to express ‘no’. First facilitated at Agile and Beyond 2018.

'No' your way to trust workshop from Marjan Venema

via: [WayBack] Facilitated my ‘No’ your way to trust workshop today at Agile and Beyond #aab18 Happy that it was well received by the audience of … mostly speakers … – Marjan Venema – Google+

–jeroen

Posted in Conference Topics, Conferences, Event, LifeHacker, Power User | Leave a Comment »

delphi – Spring4D: Why is list of type TObjectList freed automatically after iteration? – Stack Overflow

Posted by jpluimers on 2019/11/28

A nice question and even nicer answer at [WayBack] delphi – Why is list of type TObjectList freed automatically after iteration? – Stack Overflow.

It comes down to the Spring4D collection classes expecting to be accessed using interface references because they descend from TInterfacedObject which also favours interface references over object references.

If you access them solely using object references, they start out with a reference count of 0 (zero). If an operation then first increases that to 1 (one), then decreases it back to 0 (zero), the collection instance gets freed.

A few nice tips and (sometimes opposing) opinions from the question/answer thread and the referencing G+ thread [WayBack] What do you think, +Stefan Glienke? ##Spring4D – Agustin Ortu – Google+ make them well worth reading.

Some:

Instead of TObjectList<TFuu>.Create, you should use TCollections.CreateObjectList<TFuu>.
This way, you only need Spring.Collections in your uses clause
interface-only usage should be enforced by hiding the classes in the implementation, exposing only interfaces
The functions of TCollections only return interface references and – more importantly – allow for code folding starting with Spring4D 1.2.
Hiding the classes in an implementation part is not possible because then this would break any possibility to inherit from these classes and extend them (as I know people do).
Never use object references to classes that inherit from TInterfacedObject because the reference counting can kick in and destroy your instance anywhere (or manually call _AddRef/_Release).
if you want to have classes, then use System.Generics.Collections

–jeroen

Posted in Conference Topics, Conferences, Delphi, Development, Event, Software Development | Leave a Comment »

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Archive for the ‘Conference Topics’ Category

The magic Delphi ReturnAddress intrinsic

Dependencies

Delphi, compiler intrinsics and generic type matching

Delphi: A few notes on tracking down a use-after free related issue involving interfaces crashing inside System._IntfClear.

An important note first

Python – list transformation; string formatting – Stack Overflow

TFreedObject in FastMM4/FastMM4.pas at master · pleriche/FastMM4 · GitHub

Using a main check main to call a main function in Python

Delphi multi-threading: confused by TThread.Synchronize / TThread.Queue? You’re not alone. And you need to be aware of exceptions there too.

So back ensuring you can execute some code on the main thread and the questions from the G+ post:

Learn so say ‘No’: ‘No’ your way to trust workshop

delphi – Spring4D: Why is list of type TObjectList freed automatically after iteration? – Stack Overflow

Jeroen W. Pluimers on .NET, C#, Delphi, databases, and personal interests

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Recent Posts

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