Microsoft.VisualBasic.Core.Tests fails on iOS and tvOS

[mdh1418]

Microsoft.VisualBasic.Core.Tests
Microsoft.VisualBasic.Tests.InteractionTests.Command

Microsoft.VisualBasic.Core.Tests.dll   Failed: 1

Test collection for Microsoft.VisualBasic.Core.Tests.dll
Microsoft.VisualBasic.Tests.InteractionTests.Command
    Assert.False() Failure\nExpected: False\nActual:   True

test methods hanging:

src/libraries/Microsoft.VisualBasic.Core/tests/Microsoft/VisualBasic/FileIO/FileSystemTests.cs
CopyFile_FileSourceFileName_DestinationFileName_OverwriteFalse
MoveFile_SourceFileName_DestinationFileName_OverwriteFalse

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Issue Details

---

Microsoft.VisualBasic.Core.Tests
Microsoft.VisualBasic.Tests.InteractionTests.Command

Microsoft.VisualBasic.Core.Tests.dll   Failed: 1

Test collection for Microsoft.VisualBasic.Core.Tests.dll
Microsoft.VisualBasic.Tests.InteractionTests.Command
    Assert.False() Failure\nExpected: False\nActual:   True

<table>
  <tr>
    <th align="left">Author:</th>
    <td>mdh1418</td>
  </tr>
  <tr>
    <th align="left">Assignees:</th>
    <td>-</td>
  </tr>
  <tr>
    <th align="left">Labels:</th>
    <td>

`area-Microsoft.VisualBasic`, `os-ios`, `os-tvos`, `untriaged`

</td>
  </tr>
  <tr>
    <th align="left">Milestone:</th>
    <td>6.0.0</td>
  </tr>
</table>
</details>

[steveisok]

May push this beyond 6

[kotlarmilos]

The tests are failing on a device with a SIGSEGV error.

Here is a test case that can reproduce the failure:

using System;
using Microsoft.VisualBasic;

namespace HelloWorld
{
    internal class Program
    {
        private static void Main(string[] args)
        {
            try{
                Information.IsNumeric(new char[] { '1', '2', '3' }); // Bug compatible
            } catch (NullReferenceException) {
                Console.WriteLine($"Error handled!");
            }
        }
    }
}

In general, this issue occurs in both JIT and AOT configurations, while it passes on the Interpreter. The assumption is that there is a missing NULL check in virtual tail call for class interface GetTypeCode.

runtime/src/mono/mono/mini/calls.c

Lines 568 to 573 in e96321d

	if (mono_class_is_interface (method->klass)) {
	guint32 imt_slot = mono_method_get_imt_slot (method);
	emit_imt_argument (cfg, call, call->method, imt_arg);
	slot_reg = vtable_reg;
	offset = ((gint32)imt_slot - MONO_IMT_SIZE) * TARGET_SIZEOF_VOID_P;
	} else {

In the interpreter, there is a CKNULL instruction before the virtual call instruction. If this CKNULL instruction is removed, the failure occurs during this_arg->vtable in the MINT_CALLVIRT_FAST opcode.

runtime/src/mono/mono/mini/interp/interp.c

Lines 4101 to 4114 in e96321d

	MINT_IN_CASE(MINT_CALLVIRT_FAST) {
	MonoObject *this_arg;
	int slot;
	cmethod = (InterpMethod*)frame->imethod->data_items [ip [3]];
	return_offset = ip [1];
	call_args_offset = ip [2];
	this_arg = LOCAL_VAR (call_args_offset, MonoObject*);
	slot = (gint16)ip [4];
	ip += 5;
	// FIXME push/pop LMF
	cmethod = get_virtual_method_fast (cmethod, this_arg->vtable, slot);

I didn't manage to find the exact code path that is missing the null check. @vargaz Do you think that the approach is reasonable or could it be something else?

[vargaz]

The JIT doesn't emit null checks, the sigsegv signal emitted on the null dereference is convered to a NullReferenceException.

[kotlarmilos]

Good, thank you. This means that theSIGSEGV signal is expected and handled as a NullReferenceException.

[kotlarmilos]

The tests are passing both locally on a device and on tvOS CI pipeline.