Generate with no hacks correctly sized layouts

Signed-off-by: Dimitar Dobrev <dpldobrev@protonmail.com>

Author: ddobrev

src/Generator/Generators/CSharp/CSharpSources.cs

@@ -524,7 +524,13 @@ public void GenerateClassInternals(Class @class)
         {
             PushBlock(BlockKind.InternalsClass);
             if (!Options.GenerateSequentialLayout || @class.IsUnion)
-                WriteLine($"[StructLayout(LayoutKind.Explicit, Size = {@class.Layout.Size})]");
+            {
+                /// There's at least one ABI (System V) that gives to empty structs
+                /// size 1 in C++ and size 0 in C. The former causes crashes in older versions of Mono.
+                int size = @class.Layout.Size == 1 && @class.Layout.DataSize == 0 ?
+                    0 : @class.Layout.Size;
+                WriteLine($"[StructLayout(LayoutKind.Explicit, Size = {size})]");
+            }
             else if (@class.MaxFieldAlignment > 0)
                 WriteLine($"[StructLayout(LayoutKind.Sequential, Pack = {@class.MaxFieldAlignment})]");
 
@@ -2885,7 +2891,7 @@ public void GenerateFunctionCall(string functionName, List<Parameter> parameters
                 ((Method) method.OriginalFunction).IsConstructor)
             {
                 WriteLine($@"Marshal.AllocHGlobal({
-                    ((Class) method.OriginalNamespace).Layout.Size});");
+                    ((Class) method.OriginalNamespace).Layout.DataSize});");
                 names.Insert(0, Helpers.ReturnIdentifier);
             }
             WriteLine("{0}({1});", functionName, string.Join(", ", names));

src/Generator/Passes/CheckAbiParameters.cs

@@ -25,19 +25,6 @@ namespace CppSharp.Passes
     /// </summary>
     public class CheckAbiParameters : TranslationUnitPass
     {
-        public override bool VisitClassDecl(Class @class)
-        {
-            if (!base.VisitClassDecl(@class))
-                return false;
-
-            if (@class.IsDependent || @class.Layout.Fields.Count > 0 || @class.Fields.Count > 0)
-                return false;
-
-            @class.Layout.Size = @class.Layout.DataSize = 0;
-
-            return true;
-        }
-
         public override bool VisitFunctionDecl(Function function)
         {
             if (!VisitDeclaration(function))