LayoutKind.Explicit

Discussion:

LayoutKind.Explicit

Trivalik Trivalik

2012-03-08 19:23:26 UTC

In VTable is a structure:

[StructLayout(LayoutKind.Explicit, Size = 16)]
public struct VTable {
[FieldOffset(0)]
public int BaseTypeIdentifier;
[FieldOffset(4)]
public int MethodCount;
[FieldOffset(8)]
public int[] MethodIndexes;
[FieldOffset(12)]
public int[] MethodAddresses;
[FieldOffset(16)]
public uint TypeInitialized;
}

You see the size is wrong. So I want only know is there a cause of it or is this a bug. This will lead to a crash if we use that type like:
VTable[] tmpForlooking = mTypes;
VTable tmpcurrentVtable = mTypes[aType];

Me is wondering if I change the size to 20. It leads to crash in PCI.AddDevice() part in virtual string.Concat(object o) to resolve ToString() in Line:
Console.WriteLine(str + device.bus + ":" + device.slot + ":" + device.function + " " + PCIDevice.DeviceClass.GetString(device));

VMT code is here the problem.
Me is wondering that in "GetMethodAddressForType" the baseTypeIdentifier is new assigned after the for loop. Which is 100% an invalid value, because of his size. The debugger shows a length of 0xffffffff. Which cause the crash.

Any idea?

Please also try to change the size to 20 and try to run if somebody has also crashes.

Matthijs ter Woord

2012-03-09 08:05:24 UTC

Permalink

When was the TypeInitialized field added?
the mTypes field is emitted by the compiler (and therefore never assigned
to by the kernel). Can you check to see if it emits 16 or 20 bytes there?
Other thing i'm interested in, is whether it actually uses the Size field...

Your question about GetMethodAddressForType is not clear to me..... See the
code: it walks up the tree till it reaches the situation Type =
TYpe.BaseType (object)

Post by Trivalik Trivalik
[StructLayout(LayoutKind.Explicit, Size = 16)]
public struct VTable {
[FieldOffset(0)]
public int BaseTypeIdentifier;
[FieldOffset(4)]
public int MethodCount;
[FieldOffset(8)]
public int[] MethodIndexes;
[FieldOffset(12)]
public int[] MethodAddresses;
[FieldOffset(16)]
public uint TypeInitialized;
}
You see the size is wrong. So I want only know is there a cause of it or
VTable[] tmpForlooking = mTypes;
VTable tmpcurrentVtable = mTypes[aType];
Me is wondering if I change the size to 20. It leads to crash in
PCI.AddDevice() part in virtual string.Concat(object o) to resolve
Console.WriteLine(str + device.bus + ":" + device.slot + ":" +
device.function + " " + PCIDevice.DeviceClass.GetString(device));
VMT code is here the problem.
Me is wondering that in "GetMethodAddressForType" the baseTypeIdentifier
is new assigned after the for loop. Which is 100% an invalid value, because
of his size. The debugger shows a length of 0xffffffff. Which cause the
crash.
Any idea?
Please also try to change the size to 20 and try to run if somebody has also crashes.
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Trivalik Trivalik

2012-03-09 19:22:55 UTC

Permalink

There are points in code which use the size of the attribute, but there are also points where this is not the case. Thats why does it crash.

So the TODO would be:
- add on all places the evaluation of StructLayout
- remove the TypeInitialize field after success

I am right?

Post by Matthijs ter Woord
When was the TypeInitialized field added?
the mTypes field is emitted by the compiler (and therefore never assigned
to by the kernel). Can you check to see if it emits 16 or 20 bytes there?
Other thing i'm interested in, is whether it actually uses the Size field...
Your question about GetMethodAddressForType is not clear to me..... See the
code: it walks up the tree till it reaches the situation Type =
TYpe.BaseType (object)

Trivalik Trivalik

2012-03-09 20:59:55 UTC

Permalink

It seems all parts of code do use the right size.
So you are right about, thinkting that vmt this field is not using.

In the past you was the adder, without any code about him.

So you have the honor to remove them.

Matthijs ter Woord

2012-03-10 08:25:28 UTC

Permalink

this field should be used by .cctor, to tell the .cctor is needed or not.

Post by Trivalik Trivalik
It seems all parts of code do use the right size.
So you are right about, thinkting that vmt this field is not using.
In the past you was the adder, without any code about him.
So you have the honor to remove them.

field...

Post by Matthijs ter Woord
Your question about GetMethodAddressForType is not clear to me..... See

the

Post by Matthijs ter Woord
code: it walks up the tree till it reaches the situation Type =
TYpe.BaseType (object)