runtime: EnC: ExecutionEngineException after edit in struct returning method

Version:

CoreCLR 3.1 and Desktop CLR 4.7.1

Steps to Reproduce:

namespace DebuggerTest
{
    public class GenericStructReturn
    {
        public static void Main() { System.Console.WriteLine(F()); }
        public static S<object, object> F()
        {
            return new S<object, object>("Hello", "");   // Breakpoint on this line
        }
    }

    public struct S<T1, T2>
    {
        private T1 o1;
        private T2 o2;

        public S(T1 o1, T2 o2)
        {
            this.o1 = o1;
            this.o2 = o2;
        }

        public override string ToString()
        {
            return o1 + " " + o2;
        }
    }
}

In the code above, place a breakpoint inside the F() method
F5
When the breakpoint is hit, put a string in for the second constructor parameter
F5
Observe the crash

Looked into it from the Roslyn side and seems to be a CLR bug.

From feedback ticket https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1246874 /cc @tmat

About this issue

Original URL
State: closed
Created 4 years ago
Comments: 26 (23 by maintainers)

Most upvoted comments

Having looked at this issue on the back of a StackOverflow question, it appears to result from varNumber not being treated as a signed value when indexing into oldMethodVarsSorted/newMethodVarsSorted.

As a result, for special vars with negative varNumbers, instead of placing them in the space reserved at the beginning of the corresponding oldMethodVarsSortedBase/newMethodVarsSortedBase arrays for special vars, it is treated as a large positive index way off the end of the array.

Hope this helps.

cosborne83 on Jun 14, 2021

If this bug is at all representative of a broader desire to use Hot Reload as a time to revisit pre-existing EnC bugs and fix them thats probably a good discussion to have

I expect there will be others. 😉

cc: @danroth27, @LyalinDotCom

stephentoub on Mar 5, 2021

I don’t understand why the fact that it reproes on desktop has any impact on scheduling of the fix. We are spending a lot of effort on improving EnC/Hot Reload experience for .NET 6. This issue is relevant to this effort.

tmat on Mar 3, 2021

The method being modified is not generic. This should be supported.

jkotas on Jan 9, 2021