Bug 8653 - The Mono verifier doesn't complain about overlapping struct and reference types when using LayoutKind.Explicit
Summary: The Mono verifier doesn't complain about overlapping struct and reference typ...
Status: RESOLVED NOT_ON_ROADMAP
Alias: None
Product: Runtime
Classification: Mono
Component: Verifier ()
Version: unspecified
Hardware: PC Linux
: --- normal
Target Milestone: ---
Assignee: Bugzilla
URL:
Depends on:
Blocks:
 
Reported: 2012-11-29 02:51 UTC by Miron Brezuleanu
Modified: 2013-05-02 08:23 UTC (History)
4 users (show)

Tags:
Is this bug a regression?: ---
Last known good build:

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Status:
RESOLVED NOT_ON_ROADMAP

Description Miron Brezuleanu 2012-11-29 02:51:48 UTC
While working with a structure defined with [StructLayout(LayoutKind.Explicit)] and [FieldOffset(n)], I noticed that .NET throws an exception when loading the assembly if I overlap structs and references. Mono doesn't. The restriction seems to make sense in the presence of a precise GC - If I overlap my reference with a double, should I consider it a reference or a double?

Furthermore, there are weird crashes on Mono when using structures with a struct/reference overlap :-)

The code that I used: https://github.com/mbrezu/Shovel/blob/master/csharp/NShovel/Shovel/Value.cs (it is now fixed to eliminate the overlap, replace FieldOffset(8) with FieldOffset(0) to reintroduce it).

A simplified use case that is rejected by .NET and accepted by Mono:

using System;
using System.Collections.Generic;
using System.Runtime.InteropServices;

namespace TestOverlap
{
    [StructLayout(LayoutKind.Explicit)]
    public struct Value
    {
        [FieldOffset(0)]
        public double DoubleValue;
        [FieldOffset(0)]
        public object ObjectValue;
    }
    class Program
    {
        static void Main(string[] args)
        {
            Value v;
            Console.WriteLine("Hello");
        }
    }
}
Comment 1 Rodrigo Kumpera 2013-05-02 08:23:14 UTC
This is only checked if the verifier is enabled. This is by design.