When generics code need to do load the address of an array element of generic type it must emit a readonly prefix, otherwise a System.ArrayTypeMismatchException will be raised.


For example:

T[] t;
t[0].GetHashCode();

Must be compiled to:

ldc.i4.0 
readonly. 
ldelema !T
constrained. !T
callvirt instance int32 object::GetHashCode()


Right now gmcs don't emit the readonly. prefix. This applies to Array::Address magic methods as well.

See #372410 for a test case and the long explanation of why the readonly prefix is required.