CODEWITHSUNDEEP
c#.net
Jeroen
Jeroen

Reputation: 63719

Explicitly causing AccessViolationException in a .NET application

I'm debugging a pesky AccessViolationException in a rather large .NET application (one that takes down the entire process, leaving nothing but an Event Viewer entry). There's a lot of distracting things going on in that application, making root cause analysis quite hard. I would like to have a "toy problem" version, but being (at best) rusty at C++, I'm having a hard time creating a .NET application that dies with such an exception.

I've searched and found for example this somewhat old post that shows code that should throw the exception I want. But if I compile this:

static unsafe void Main(string[] args)
{
    Console.WriteLine("Doing stuff");

    try
    {
        int foo = (*((int*)0));
    }
    catch (AccessViolationException)
    {
        Console.WriteLine("Don't want to reach this.");
    }

    Console.WriteLine("Waiting");
    Console.ReadKey();
}

Or this:

static unsafe void Main(string[] args)
{
    Console.WriteLine("Doing stuff");

    try
    {

        int foo;
        int* ip = null;
        foo = *ip; //crash!
    }
    catch (AccessViolationException)
    {
        Console.WriteLine("Don't want to reach this.");
    }

    Console.WriteLine("Waiting");
    Console.ReadKey();
}

PS. The catch block is there because my actual scenario I'm trying to represent is one where I cannot catch the exception either (so I cannot just throw it myself).

with the "Allow unsafe code" option on, in a fresh .NET Console application, it crashes with a Null Reference Exception, not an AccessViolationException. Although I'm not all too surprised, and kind of understand why that is the case, I'm still left with the original problem.

Bottom line:: is there an easy way to create a .NET application that causes an AccessViolationException on demand, preferably in a way that the process completely dies without the option of exception handling, leaving only a trace in the Event Viewer?

Upvotes: 2

Views: 162

Answers (3)

Jeroen
Jeroen

Reputation: 63719

Colleague came up with a version that doesn't even need unsafe code:

using System;
using System.Runtime.InteropServices;
using static System.Console;

class Program
{
    static void Main(string[] args)
    {
        WriteLine("Doing stuff");

        try
        {
            Marshal.StructureToPtr(1, new IntPtr(1), true);
        }
        catch (AccessViolationException)
        {
            WriteLine("Should not reach this.");
        }
        finally
        {
            WriteLine("Should not reach even this.");
        }

        WriteLine("Waiting");
        ReadKey();
    }
}

The try block's statement will kill the whole thing, no other code is executed, not even the finally block.

Upvotes: 0

Andrei
Andrei

Reputation: 98

Also, if you don't want to use "unsafe" in C#, you can create simple C++ CLR project in your solution and do everything you want with memory and other resources. ))

using namespace System;
namespace ClassLibrary1 {

public ref class Class1
{
    // TODO: Add your methods for this class here.
public:
    void ThrowException()
    {
        int * p = (int*)-1;
        *p = 10;
    }
};

}

This method give us AccessViolationException.

Upvotes: 2

Anton Samsonov
Anton Samsonov

Reputation: 1422

Replace 0 (or null) with -1 — it should trigger the desired behavior because −1, when implicitly casted to a pointer, results in 0xFFFFFFFF… which usually belongs to kernel-mode address space (both in Windows and *nix) that you are not allowed to read from user-mode programs.

Upvotes: 5

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