Fix buffer overflow in Garbage Collector

[MateuszKlatecki]

Description

Due to an error in the Garbage Collector, HardFault occurred. The error relates to incorrect stack switching and as a result to buffer overflow and overwriting of data on the CLR thread stack.

Motivation and Context

• Fixes GC

How Has This Been Tested?

Tested with following code.

public class Program
{
    public static void Main()
    {
        ArrayList a = new ArrayList();
        TestClass prev = null;

        while (true)
        {
            TestClass t = new TestClass(200);
            a.Add(t);
            t.prev = prev;
            if (a.Count > 200)
            {
                a.RemoveAt(0);
            }
            prev = t;
            Debug.GC(false);

        }
        Thread.Sleep(Timeout.Infinite);

    }
}

public class TestClass
{
    readonly TestClass t;
    public TestClass prev;
    public TestClass(int num)
    {
        if (num > 0)
        {
            t = new TestClass(num - 1);
        }
    }
}

Screenshots

Types of changes

• Improvement (non-breaking change that improves a feature, code or algorithm)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

Signed-off-by: Mateusz Klatecki [email protected]

[nfbot]

Hi @MateuszKlatecki,

I'm nanoFramework bot.
Thank you for your contribution!

A human will be reviewing it shortly. 😉

[josesimoes]

This is a big one!! A bug this serious in the GC?!?! 😱 😱 😱

Well done!! 👏 💯

[MateuszKlatecki]

I think there is also another bug in GC in Heap Compaction, but I haven't had time to look at it yet. In our device I disabled HeapCompaction by setting flag NoCompaction in ClrStartup

[josesimoes]

Interesting... care to raise an issue so this gets in the queue?

[josesimoes]

Hitting the changed code in virtual nanoDevice:

Before the fix: