How to view code through disassembler ildasm? Throws an error.

If you are a developer or someone who is interested in understanding how software applications work behind the scenes, you may have come across the ildasm disassembler tool. This powerful tool allows you to view the Intermediate Language (IL) code of .NET assemblies, giving you insights into the inner workings of the applications.

However, like any other software tool, the ildasm disassembler is not immune to errors. If you are encountering an error while trying to view code through the disassembler, it can be frustrating and hinder your progress. But fear not! In this article, we will explore some common reasons for the error and provide potential solutions to help you troubleshoot the problem.

One possible reason for the error could be an incompatibility between the version of the disassembler tool and the .NET assembly you are trying to analyze. It is essential to ensure that you are using a compatible version of the disassembler tool that matches the framework version used to compile the assembly. Trying to disassemble a newer or older version of the assembly with an incompatible disassembler can lead to errors.

Another reason could be related to the permissions or access rights of the assembly file. If the file is located in a restricted directory or if you do not have the necessary permissions, the disassembler may encounter errors while trying to access the file. Check the file’s location and make sure you have the required permissions to read the file.

What is ILDASM disassembler?

ILDASM, short for IL Disassembler, is a tool provided by the .NET Framework that allows you to view and analyze the Intermediate Language (IL) code of .NET assemblies. ILDASM can be used to examine the contents of compiled .NET assemblies, including metadata, types, methods, and their IL instructions.

When a .NET program is compiled, it is translated into a platform-independent bytecode called IL. This IL code is then executed by the .NET runtime to produce the desired output. ILDASM allows you to reverse-engineer this IL code and understand how the .NET program works at a low-level.

With ILDASM, you can navigate through the different components of a .NET assembly, such as modules, types, and methods. You can inspect the metadata of each component, including its name, visibility, and custom attributes. By exploring the IL instructions of a method, you can get insights into its behavior and how it interacts with other parts of the program.

Additionally, ILDASM provides features for exporting the IL code to a text file or a Visual Studio project, which can be useful for further analysis or modification of the code.

However, it’s important to note that ILDASM should be used for educational and analysis purposes only. Reverse engineering and modifying the IL code of a compiled .NET assembly without proper authorization and legal rights may violate intellectual property laws.

Viewing code through ILDASM

What is ILDASM?

ILDASM, or IL (Intermediate Language) Disassembler, is a tool provided by Microsoft that allows you to view the IL code of a .NET assembly. ILDASM converts the binary code of a compiled assembly into a human-readable format, making it easier to understand and analyze.


To use ILDASM, follow these steps:

  1. Open the ILDASM tool on your computer. It is typically located in the .NET Framework directory (e.g., C:\Windows\Microsoft.NET\Framework\v4.0.xxxxx).
  2. Once the ILDASM tool is open, go to File and select Open.
  3. Navigate to the directory where the assembly you want to disassemble is located.
  4. Select the assembly file (with the .dll or .exe extension) and click Open. The assembly will now be loaded into ILDASM.
  5. Double-click on the assembly in the tree view on the left-hand side of the ILDASM window to expand it and see its contents.
  6. Expand the MANIFEST folder to see the assembly’s metadata.
  7. Expand the TYPE folder to see the classes and types within the assembly.
  8. Double-click on a specific type to view its IL code in the right-hand side of the ILDASM window.

Interpreting the IL code

The IL code displayed by ILDASM represents the low-level instructions that make up the .NET assembly. It is important to note that the IL code is not the original source code but rather a lower-level representation of it.

Here are a few tips for interpreting the IL code:

  • OpCodes: Each IL instruction is represented by an opcode (e.g., ldstr, call, add, etc.), which determines the action to be performed.
  • Operands: Most opcodes are followed by one or more operands, which provide additional information or arguments for the instruction.
  • Branching: Branching instructions (e.g., br, brtrue, brfalse, etc.) control the flow of execution in the IL code. They determine which instruction to execute next based on certain conditions.
  • Stack: The IL code often operates on a stack, pushing and popping values as needed. Instructions such as ldloc, ldarg, ldstr, ldc, and stloc manipulate the stack.


Using ILDASM to view the IL code of a .NET assembly can be a valuable tool for understanding how the assembly works and troubleshooting issues. By interpreting the IL code, you can gain insights into the inner workings of the assembly and optimize your code accordingly.

Step 1: Open ILDASM

To view code through ILDASM disassembler, the first step is to open the ILDASM tool. ILDASM is a command-line tool included with the .NET Framework SDK.

To open ILDASM, follow these steps:

1. Open the Command Prompt or the Developer Command Prompt for Visual Studio.

2. Navigate to the directory where the ILDASM tool is located. By default, it is located in the following directory:

C:\Program Files (x86)\Microsoft SDKs\Windows\v10.0A\bin\NETFX X.X Tools\

Note: Replace «NETFX X.X» with the version number of .NET Framework installed on your system.

3. Once you are in the directory, type «ildasm» and press Enter to run the ILDASM tool. This will open the ILDASM user interface.

Now that you have opened ILDASM, you can proceed to the next steps to view the code using this disassembler.

Step 2: Load the assembly

Once you have opened the ILDASM disassembler, you will need to load the assembly that you want to view the code for. Follow these steps to load the assembly:

  1. Click on the «File» menu at the top left corner of the ILDASM window.
  2. Select the «Open…» option from the dropdown menu. This will open a file browser window.
  3. Navigate to the location of the assembly that you want to view and select it.
  4. Click on the «Open» button to load the assembly into ILDASM.

Once the assembly is loaded, you will be able to see the metadata and the IL code for the assembly’s types and methods. You can navigate through the code using the tree structure on the left side of the ILDASM window.

Note that ILDASM can only disassemble managed assemblies, and not native code or mixed-mode assemblies. If you try to load an unsupported assembly, you may get an error message indicating that the assembly is not a valid CLR assembly.

By following these steps, you should be able to load the assembly into ILDASM and view the code for the assembly’s types and methods. This can be a valuable tool for understanding how a .NET assembly works and for troubleshooting issues in your code.

Step 3: Navigate to the code

Once you have opened the ILDASM disassembler and loaded your .NET assembly, you will need to navigate to the specific code you want to view. Follow these steps:

  1. Expand the tree structure in the left pane of the ILDASM window to locate the desired assembly.
  2. Expand the assembly to view its constituent modules.
  3. Double-click a module to see its classes and resources.
  4. Double-click a class to view its members (such as methods, fields, and properties).
  5. Double-click a member to see its IL code on the right side of the window.

By following these steps, you can easily navigate through the IL code of your assembly and view the disassembled code. It is important to note that the IL code may not be as readable as the original source code, but it can still provide valuable insights into the internal workings of your application.

Error in ILDASM

When trying to view code through ILDASM disassembler, you may encounter errors that prevent you from accessing the desired information. These errors can be frustrating, but they can usually be resolved by following these troubleshooting steps:

  1. Check if the file you are trying to disassemble is in the correct format. ILDASM works best with files compiled in the .NET framework.
  2. Make sure you have the necessary permissions to access the file. If you are encountering errors while trying to disassemble a protected assembly, it may be due to insufficient permissions.
  3. Verify that ILDASM is installed correctly on your system. Reinstalling ILDASM or repairing the installation may resolve any issues related to its functionality.
  4. Ensure that you are using the correct version of ILDASM for the assembly you are trying to disassemble. ILDASM versions can vary depending on the .NET framework version used in the assembly.
  5. Update your .NET framework installation to the latest version. Outdated frameworks may not be compatible with ILDASM, resulting in errors.
  6. If you are disassembling a large assembly, try disassembling it in smaller chunks to see if that resolves the error. Sometimes, ILDASM may struggle with large assemblies.
  7. Search online for specific error messages you encounter during the disassembly process. You may find discussions or solutions provided by other developers who have encountered similar issues.

By following these steps, you should be able to resolve most errors encountered while using ILDASM. If the problem persists, it may be a good idea to seek assistance from the developer community or the support channels provided by the ILDASM tool.

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