Switching on Silverlight

“Web is approaching the desktop” – Wahid Bhai said while demonstrating the new Flex project at KAZ. Flex is Flash but on steroids… well to be truthful Flex is Flash with libraries and an easy programming model and the nicest of all - a good eclipse based IDE.

Microsoft has of course an answer to Flex - The Silverlight which used to be known as WPF/e for a while. In Microsoft’s wording:

“Silverlight is Microsoft’s latest technology to design interactive web client with truly object oriented language C# with full support of VB .NET and other .NET citizens. Microsoft® Silverlight™ is a cross-browser, cross-platform plug-in for delivering the next generation of .NET based media experiences and rich interactive applications for the Web … Silverlight offers a flexible programming model that supports AJAX, VB, C#, Python, and Ruby, and integrates with existing Web applications. Silverlight supports video to all major browsers running on the Mac OS or Windows…. ” (the babble continues promising cure for cancer, food for Sudan and even the impossible - patriotism for the Bangladeshi middle class!)

Back on Earth, we the “Psycho group” at KAZ had a week of free time in between projects. So in the time honored way at KAZ we decided to do a spacer project to try out silverlight in all its Alpha glory and MS’s super hype! We decided to make a webtop with silverlight that would show an abstracted backend filesystem exposed by WCF.

This post is about our pains and joys during the project. Not gifted with great writing skills (apart from the coding kind) I will try putting down disperate items that we learnt or I felt like telling about our project.

First principle


Starting from Silverlight 1.1 the managed code is supported at client side. We decided to be very strict in this project to use only managed code for programming- no JavaScript. Like all principles this soon turned out to be a pain in a not so polite place

Installing Silverlight

To develop with Silverlight 1.1 you need Visual Studio 2008 (code name Orcas). While writing this downloadable beta version is available from Microsoft site. You also need Silverlight 1.1 plug-in distribution – alpha is available while writing this. Though not necessary the Silverlight 1.1 SDK is highly recommended. The SDK includes controls, samples, documents which may be useful to start. Please note that the Silverlight plug-in is required on any client from where the site is viewed.

Controls that comes from Boss

None!

Well not exactly true, but close enough. Silverlight 1.1 alpha distribution comes with a very limited set of controls. It has controls like rectangle, ellipse and label, canvas. It does not include button, edit box, scroll bar or any other advanced control. The SDK includes some controls like scrollbars.


Our Architecture

With no major controls available and no infrastructure for a shell, we soon realized that we need a petzold like approach to the project. We actually need to create a windowing system and the bare basics of message management.

Our final designe came out with 3 layers. Top layer is the application layer where user applications run. Middle layer is kernel which controls the events and communication between applications. It also provides a set of API for application developers. The lowest layer is an abstraction layer to communicate with the web server.

The system provides API’s for application developers for the platform while hiding the http calls – making the application development similar to desktop application development. Web call abstraction layer does that for user application.

The Kernel

The controller behind the scene controls form events, focus of controls, controls and windows to common file operations. The kernel has four main parts:

• • Messaging System and Focus Manager
  • Window Manager
  • Process Manager
  • File system Driver
  • Resource Manager

Messaging System and Focus Manager

An event first comes to this manager and depending on the type routed to controls. If the user clicks on a control the focus manager updates the focus of controls. It keeps track of current on focus control. If it finds a change in focus it send OnLostFocus call to old control and OnSetFocus call to new focused control. With this exception most messages are routed to the focused control on arrival.

Window Manager

The window manager keeps track of each window that is created on the system. At any time window manager provides the list of windows currently available in the system. A utility application like TaskManager or TaskBar can use the list for display and control the windows. In our case the TaskBar buttons are created from the list and user can control minimize or restore operation from the TaskBar application. To keep track of the windows the window manager uses an internal generic Window list. When a new window is created the window is registered with window manager and when a window is disposed the window is unregistered.

Process Manager

The SilverlightDesktop applications that are created by implementing the IApplication interface in the main class are managed by the process manager. The process manager exposes a service to create a new process. It accepts class name as its first parameter and other parameters are passed through a Parameter object that can contain strings. On success the process manager returns a Instance object that can identify the process. Simplified version of Instance class is like this –

public class Instance{ public int Handle; public int ParentHandle; public string Name; }

The returned interface object can uniquely identify the process and it is required to handle the process.

Designing a new control

ControlBase class can be extended to design a custom control. The control may have a xaml also. The ControlBase getter ResourceName of type string should be overirden to specify the name of the xaml resource in the assembly. It is also possible to set the assembly of the control. The constructor of ControlBase class iterates through each resource and look for the specified resource to get the right xaml resource. Same technique is used in the Silverlight SDK. For example we want to have a icon control that has a image and text. Our xampl file would be similar to this:

<Canvas xmlns=”http://schemas.microsoft.com/client/2007”
xmlns:x=”http://schemas.microsoft.com/winfx/2006/xaml”
Width=”32″ Height=”50″ x:Name=”_container" >
<Canvas x:Name=”_icon” Width=”32″ Height=”32″ Canvas.Left=”0″ Canvas.Top=”0″/>

<TextBlock x:Name=”_name” Width=”80″ Height=”15″ Canvas.Left=”-24″ Canvas.Top=”32″ />
</Canvas>

We used a Canvas for icon, a TextBlock for label and a container canvas to hold them both.

And our code back for the control would be:

We used a Canvas for icon, a TextBlock for label and a container canvas to hold them both.And our code back for the control would be:

public class Icon : ControlBase{
Canvas icon;
TextBlock text;
Canvas container;
protected override void OnInitialized() {
icon = actualControl.FindName(”_icon”) as Canvas;
text = actualControl.FindName(”_name”) as TextBlock;
container = actualControl.FindName(”_container”) as Canvas;
}
protected override string ResourceName {
get {
return “Icon.xaml”;
}
}
}

Now if we add some getter/setter we get the icon control ready to be used.

The Window

Window is a customized control- but is different from others. It uses mouse events to implement feature like drag/ drop, has a title bar and sizing buttons for minimize to system taskbar, maximize to cover full user desktop area or close button to close and dispose the control from the system.

It was first posted at http://www.kaz.com.bd/blog/index.php/?p=10

MISL to C# (Sharp) -> Loops - the simple cases

I wish, as a decompiler writer, there would be no loops. Programmers use thousands of goto statements with if statements. But as it is not the case I must understand how to parse MSIL instructions that were generated from the loops.

Of the three types of most common loops (for, while, do-while) the while loop is the basic one. The block that is generated from any type of these loops usually has a conditional jump (usually a brtrue.s ) as the last instruction of the block. The difference from if structure is- the instruction jumps to an offset less than current instruction offset. The for and while loop has a unconditional branch (br.s ) to an offset that is between start and end of the block. The jump target usually at the beginning of the condition checking instructions. The do-while loop lacks this branch for the reason - it does not test the condition before it is at the end of the block.

So, we get instruction block like following MSIL block:

-------------------------------------------------------------------------------------
IL_0010: br.s IL_005a ;do-while loop does not have this line
IL_0012: nop

[any type and number of instructions]

IL_0059: nop

[condition check instruction- results boolean value on stack]

IL_0060: brtrue.s IL_0012
-------------------------------------------------------------------------------------

On my previous post on if structure I showed how to create a boolean condition for if structure. Things are similar here for the loops. Follow the instructions - get the top stack element when conditional jump found - reverse it (add just an !) for brtrue.s jump and put it as the loop statements condition statement. Please note that the conditional jump targets the instruction just at or after the starting instruction of the block.

Here we find we can not have a single passing decompiler. We must identify the code blocks in an iteration before final iteration. Till now we can identify blocks of if, for, while, do-while structures by using conditional jump instructions and their destination. If has destination offset after the current offset and others have destination before the current offset. The for and while can not be distinguished very clearly but the do-while does not have a jump at the beginning. And of course there can be nested blocks that are generates from nested loops.

There is some complex variation of the loops - like infinite loops, forcach loop etc. They are not much different. But I want to discuss the control structure later in more detail. This post is little bit more theoretical- see you again very soon with more interesting things.

MISL to C# (Sharp) -> Iff (if and only if)

Today I’ll talk about the most basic and useful if-then structure. The compiler generates a conditional branch. We create a block of instructions for the structure. The block is separated by the branch instruction (like brtrue) and the branch label (like IL_0019 - where the code jumps). And our condition is on the stack. If we find a true condition branch we negate it and put it as a if statement condition. The block is initially a block of MSIL that we will convert to C# code later (
may need recursion here??). Please note that the labels are not stored in MSIL. It is just the byte offset of the MSIL in a method.

If you have not already read you are requested to read my previous post.


We take a simple method to test our theory.

public int IfStructure(int a, int b)
{
bool CS_4_0001;
if (a < b)
{
System.Console.Write("Condition is true");
}
return b;
}

Here is the MSIL code generated by Visual Studio 2005 compiler.

.method public hidebysig instance int32 IfStructure(int32 a, int32 b) cil managed
{
// Code size 31 (0x1f)
.maxstack 2
.locals init ([0] int32 CS$1$0000,
[1] bool CS$4$0001)
IL_0000: nop
IL_0001: ldarg.1
IL_0002: ldarg.2
IL_0003: clt
IL_0005: ldc.i4.0
IL_0006: ceq
IL_0008: stloc.1
IL_0009: ldloc.1
IL_000a: brtrue.s IL_0019

IL_000c: nop
IL_000d: ldstr "Condition is true"
IL_0012: call void [mscorlib]System.Console::Write(string)
IL_0017: nop
IL_0018: nop

IL_0019: ldarg.2
IL_001a: stloc.0
IL_001b: br.s IL_001d
IL_001d: ldloc.0
IL_001e: ret
} // end of method ControlStructures::IfStructure

We now start parsing:
-------------------------------------------------------------------------------------
.method public hidebysig instance int32 IfStructure(int32 a, int32 b) cil managed
{
// Code size 31 (0x1f)
.maxstack 2
.locals init ([0] int32 CS$1$0000,
[1] bool CS$4$0001)
--

These lines generate output that we do without any processing of MSIL. There is method definition and local variables. We change the local variable names to C# current names without conflict. For simplicity here we just replace '$' with '_'. One thing to evaluate the MSIL instructions we must keep a map of local variables with variable number. In this example CS$1$0000 is local variable 0 of type int. For clarity we do not show the map here. A simple STL map should work.

Output:
public int IfStructure(int a, int b)
{
int32 CS_1_0000;
bool CS_4_0001;

Stack: [Empty]

-------------------------------------------------------------------------------------
IL_0000: nop
IL_0001: ldarg.1
IL_0002: ldarg.2
--
So we push method argument 1 and 2 to stack:

Output: [None]

Stack:
a,b

-------------------------------------------------------------------------------------
IL_0003: clt
--

This instructs us if stack top-1 is less than stack top. The two elements are popped from stack and result goes to stack. No output of course.

Output: [None]

Stack:
a<b

-------------------------------------------------------------------------------------
IL_0005: ldc.i4.0
--

Load (aka push) constant integer of value 0 on stack.

Output: [None]
Stack: a<b,0
-------------------------------------------------------------------------------------
IL_0006: ceq
--

Check if stack top-1 equals stack top. Result goes to stack.
Output: [None]
Stack: a < b == 0

-------------------------------------------------------------------------------------
IL_0008: stloc.1
IL_0009: ldloc.1
--

What else? Store stack top in local variable 1 and load that on tack again. We decided previously when we store some value in a local variable we use assignment to that variable and output that code. For clarity I added parentheses:

Output:CS_4_0001 = (a < b == 0)
Stack:CS_4_0001

-------------------------------------------------------------------------------------
IL_000a: brtrue.s IL_0019
--

We have got a conditional branch. We create a block starting from here to IL_0019. And put them in curly braces. And our condition is on the stack. We find a true condition branch so we negate it and put it as if structure as I said at the beginning.

Output:
if(!CS_4_0001)
{
IL_000c: nop
IL_000d: ldstr "Condition is true"
IL_0012: call void [mscorlib]System.Console::Write(string)
IL_0017: nop
IL_0018: nop
}

Stack: [Empty]

-------------------------------------------------------------------------------------
IL_0019: ldarg.2
IL_001a: stloc.0
IL_001b: br.s IL_001d
IL_001d: ldloc.0
IL_001e: ret

We do not parse them here. They are very simple to understand.
===========================================================

Ok we now can work on little more complex code3s than easiest. This will also produce codes that was generated by "for structure" but in a funny way. If we add a little more intelligence to produce "goto" output code for special branching that we cannot handle with if, we get following result.

The code like this:


for(int i=0;i<10;i++)
{
...
}
...

will be converted to:

int i;
i=0;
label_1:

if(i<10)
{
---
i++;
goto label_1;
}
...

For is not our today’s material. We'll look at loops next time.

=====================================================================================
Now you may find that our theory generates a funny code block like:

CS$4$0001=((a<b)==0);

if(!CS$4$0001)
{

---

}


Here the optimization comes to scene. But we skip them for future.

MSIL to C# -> The theory development begins

Welcome to my journey of writting a .NET assembly decompiler.

First of all I am trying to develop a theory to decompile MSIL. I just do whatever a MSIL instruction ask me to do. But I do it keeping in mind that I am decompiling MSIL. So when it asks to push me a value of a variable I push the name of that varuiable on stack.

To understand the code it is required that you know or have a reference of what each isntruction
of MSIL actually does.

Here is sample program to test if our concept works:

namespace DisasmIL
{
class Math
{
public int add(int x, int y)
{
return x + y;
}
}

class Program
{
static void Main(string[] args)
{
Math m;
int a, b;
m = new Math();
a = 20;
b = 50;
int p = m.add(a, b);
}
}
}

We only check one method. The Main method.When the Main method is
compiled it takes following form.
.method private hidebysig static void Main(string[] args) cil managed
{
.entrypoint
// Code size 23 (0x17)
.maxstack 3
.locals init (
[0] class DisasmIL.Math m,
[1] int32 a,
[2] int32 b,
[3] int32 p
)
IL_0000: nop
IL_0001: newobj instance void DisasmIL.Math::.ctor()
IL_0006: stloc.0
IL_0007: ldc.i4.s 20
IL_0009: stloc.1
IL_000a: ldc.i4.s 50
IL_000c: stloc.2
IL_000d: ldloc.0
IL_000e: ldloc.1
IL_000f: ldloc.2
IL_0010: callvirt instance int32 DisasmIL.Math::'add'(int32,int32)
IL_0015: stloc.3
IL_0016: ret
} // end of method Program::Main
=============================================================

We parse line by line:
------------------------------------------------------------------------
.method private hidebysig static void Main(string[] args) cil managed

It is method declaration with default starting curly brace.
Output code:
static void Main(string[] args)
{
Stack: [empty]
------------------------------------------------------------------------
.entrypoint
// Code size 23 (0x17)
.maxstack 3
.locals init (
[0] class DisasmIL.Math m,
[1] int32 a,
[2] int32 b,
[3] int32 p
)

Need not to be explained. They are self explanatory. Declare variables.
Output code:
DisasmIL.Math m;
int a;
int b;
int p;
Stack:
------------------------------------------------------------------------
IL_0000: nop:

Does nothing (nop).
Output code: [none]
Stack: [empty]
------------------------------------------------------------------------
IL_0001: newobj instance void DisasmIL.Math::.ctor()

Create new instance of DisasmIL.Math using default constructor
so we push "new DisasmIL.Math()" on our stack.
Output code:
Stack: new DisasmIL.Math()
------------------------------------------------------------------------
IL_0006: stloc.0

So we pop top of stack and assign it to local variable 0.
Output code:
m = new DisasmIL.Math();
Stack: [empty]
------------------------------------------------------------------------
IL_0007: ldc.i4.s 20

What we do is push constant 20 on stack.
Output code: [none]
Stack: 20
------------------------------------------------------------------------
IL_0009: stloc.1

So we pop top value and assign it to local variable 1.
Output code:
a = 20;
Stack: [empty]
------------------------------------------------------------------------
IL_000a: ldc.i4.s 50

We push constant 50 on stack.
Output code: [none]
Stack: 50
------------------------------------------------------------------------
IL_000c: stloc.2

We pop top value and assign it to local variable 2.
Output code:
b = 50;
Stack: [empty]
------------------------------------------------------------------------
IL_000d: ldloc.0
IL_000e: ldloc.1
IL_000f: ldloc.2

Push local variable 0, 1 and 2 on stack.
Output code:
Stack: m, a, b
-------------------------------------------------------------------------
IL_0010: callvirt instance int32 DisasmIL.Math::'add'(int32,int32)
IL_0015: stloc.3

We call add method with values top-1, top of stack for instance of
top-2. For any method call if it returns value it is returned on
stack. So check next instruction. If it is a stloc then we assign the
return value. We assign return value to local variable 3.

Output code: p=m.add(a,b);
Stack:
--------------------------------------------------------------------------
IL_0016: ret

Return void. So no code except closing curly brace.
Output code:
}

Stack: [empty]

Now if you add the output codes together you'll find the original C# code is generated. This works for simple cases. Need to test if it works for complex situations. Miles to go....