The blog post from PostSharp that you found is actually about solving a different problem - the incompatibility of PostSharp 2.1 itself with obfuscation tools. PostSharp 3.0+ is already compatible with obfuscation tools and the blog post is not relevant for these newer versions.
Your problem is different though - I suspect that your logging code accesses the name of the class during run-time and thus receives an obfuscated class name. You should try to prepare a logging format string during compile time and store it in the aspect's field. This way you can store an original class name in your string and access it during run-time.
[Serializable]
public sealed class TraceAttribute : OnMethodBoundaryAspect
{
private string enteringMessage;
public override void CompileTimeInitialize(MethodBase method, AspectInfo aspectInfo)
{
string methodName = method.DeclaringType.FullName + method.Name;
this.enteringMessage = "Entering " + method.DeclaringType.FullName + method.Name;
}
public override void OnEntry(MethodExecutionArgs args)
{
Console.WriteLine(this.enteringMessage);
}
}