calli with [out] struct containing byvalarray fields leave fields uninitialized

Having a struct with byvalarray:

public struct testData {
	public int x;
	public int y;
	[MarshalAs (UnmanagedType.ByValArray, SizeConst = 256)]
	public byte[] data;
	public int z;
	public int w;
}

Creating a DynamicMethod with indirect call to c library automatically initialize the array fields. The c func signature is: void getData (struct testData* pData){}.

DynamicMethod method = new DynamicMethod ("test", null, new Type[] { typeof (testData).MakeByRefType () });
ILGenerator gen = method.GetILGenerator ();
gen.Emit (OpCodes.Ldarg_0);
gen.Emit (OpCodes.Ldc_I8, funcPtr.ToInt64 ());
gen.Emit (OpCodes.Conv_I);
gen.EmitCalli (OpCodes.Calli, CallingConvention.StdCall, null, new Type[] { typeof (testData).MakeByRefType () });
gen.Emit (OpCodes.Ret);

I call the dynamic method delegate with (out testData data) inline declaration, and arrays are initialized. Trying to do the same with Cecil using the CallSite class to make the call, arrays are Null. Am I missing something to have arrays initialized?

[jbevain]

No clue sorry. I’m going to close this, feel free to re-open with a self-contained if you end up finding out that Cecil generates something wrong.

[jpbruyere]

I’m on linux, but with localinit on/off, nothing change and also I don’t use local with this [out] parameter. byvalArrays must be initialized by some piece of code in Marshaling, default ctor of such structs leave arrays to null, and trying to init them manually (with new byte[256]) destabilize the runtime. but PtrToStruct (hGlobHnd), classic PInvoke, and calli through a dynamic method initialize the arrays. My intuition is that there is a flag somewhere (assembly, module, method) that enable or not such fixed array init, but I may be completely wrong. I should handle more tests on my side, I was asking here hoping someone already know something about this problem.