C# P/invoke structure alignment

Question

I'm trying to call NtGetContextThread from C# on AMD64. The problem is that the CONTEXT structure for AMD64 needs to be aligned on a 16-byte boundary, and when I call NtGetContextThread I always get STATUS_DATATYPE_MISALIGNMENT. I'm aware that C# can align individual members of a struct using the Pack attribute, but it doesn't seem to be able to align the entire structure. Is there any way I could do this?

EDIT: Just to make it clear, I don't want to align individual members. I want to align the entire structure.

Answer 1

From your question, it's not clear whether you fully understand the Pack property of the StructLayout attribute. See this msdn article for more information.

If I understand you correctly, what you're looking for is the ability to explicitly align each member of a struct individually. If that's your goal, you can do so using the StructLayout and FieldOffset attributes as follows:

[StructLayout(LayoutKind.Explicit)]
public struct Message
{
    [FieldOffset(0)]
    public int a;
    [FieldOffset(4)]
    public short b;
    [FieldOffset(6)]
    public int c;
    [FieldOffset(22)] //Leave some empty space just for the heck of it.
    public DateTime dt;

}

Beware, though, that the the .NET CF Marshaler has some rules that you may not expect. For example, arrays must always be aligned at 4-byte boundaries. There are workarounds for this issue, but you should be aware that problems like this may crop up.