How to decompile dll and exe files properly and convert the decompiled code to the correct source code

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Hi Guru,
I am newbie programmer with the little experience and having some knowledge of C# and Asp.net.
I am currently assigned to make the changes for some pages of the C# window application that is using Webservice (C# 4.0, .Net Framework 4.0). I don't have the source code for the project but exe and dll files only (a few dll files in bin folder and 3 exe files, a few .resx files, .asmx files and web config outsides of the bin).

After searching through the google, I understand that I need to used the reflector tools to decompile the code and reflexil plugin to change the code. I have decompiled all of the exe and dll files of the application and lastly I got the source code with a lot of errors. However, I don't see any design page and don't have any idea whether the solution structure is correct or not since I have not seen the source code before at all.I really need the help from you.I would like to get the correct source code and solution structure.

It would be deeply appreciated if someone can tell me
1) What is the proper way to decompile ? (Do I need to decompile both exe files and dll or either one?)
2) Which is the better way to change the code? (via reflector with reflexil or Visual Studio)
3) May I have some links that explain well how to convert the decompiled code (auto-generated code) to the correct source code?
4) How shall I do in order to get design page (all I see is .cs page)?
5) How to check the current solution structure is correct or not?

Please let me know if any further information is required to provide.
Thank you so much in advance for your kind advice.

Note:The previous programmer left the company and don't have the source code.

Posted 9-Jan-14 17:17pm

Kaysikarline

Updated 16-Jul-18 2:00am

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Kaysikarline 10-Jan-14 0:01am

Referring to Q3:
How to edit the decompiled code?
For example, I have the decompiled code as follows:
[
private bool MoveNext()
{
switch (this.<>1__state)
{
case 0:
this.<>1__state = -1;
this.<count>5__1 = 0;
while (this.<count>5__1 < 10)
{
this.<>2__current = this.<count>5__1;
this.<>1__state = 1;
return true;
Label_004B:
this.<>1__state = -1;
this.<count>5__1++;
}
break;

case 1:
goto Label_004B;
}
return false;
}
]
Do I need to change that as below?
[
static IEnumerator GetCounter()
{
for (int count = 0; count < 10; count++)
{
yield return count;
}
}
]

GKP1992 16-Jul-18 8:06am

You should not stay where you are working right now. Leave asap.

2 solutions

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Ron Beyer · Answer 1 · 2014-01-09T17:26:00

I've always had problems with decompiling and Reflector, try DotPeek[^].

1. You only really need to decompile the one you need to modify. If you change an API in the DLL it may require you to change the EXE.

2. There are tools out there that let you work directly on MSIL and modify inside the tool, but I would prefer to go back to code and recompile the entire thing. The "best" one is the one that works in your situation with the least amount of effort.

3. I'm not sure what you mean "correct" source code. If you mean the code without errors, try the tool I linked above. It will convert to C# and people have had good results with it. No tool is 100% effective though since the compiler may include optimizations that are not possible to replicate in source.

4. A lot of decompilers (Reflector is one with this problem) doesn't make separate Designer.cs files. I'm not sure if DotPeek will create designer files but there isn't a good way around this. Designer files exist for the pure reason to make it easier to separate designer code from user code, after it runs through the compiler its impossible to determine if it was designer generated or user generated.

5. The solution structure is the one that compiles, technically folders and internal structure of the solution are only there to make it easy to organize code, and again, this structure is not replicated in the compiled file. The decompiler has no way of knowing how this was laid out (it can guess based on namespaces), but there is no way to duplicate the original structure. As long as all the files are there and compiles back into the right namespaces and types, its as good as you can hope for.

johannesnestler · Answer 2 · 2018-07-16T02:00:00

I have done such things in the past….
Source Code was lost - only the binaries left.

I started with creating a new Project (Windows application, .NET 4 in your case).
Then tried to fill up with the decompiled code -piece by piece. Hopefully you will find out that maybe there is no need to decompile the dlls because you don't have to change anything there.

So at least you end with something managable for the future...

How to decompile dll and exe files properly and convert the decompiled code to the correct source code

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How to decompile dll and exe files properly and convert the decompiled code to the correct source code

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