[mono][interp] Attempt to interpret m2n wrapper if it is not found in…

… aot image (dotnet#100025)

* [mono][interp] Remove old hack

interp_create_method_pointer should only ever return a function pointer callable from compiled code.

* [mono][interp] Attempt to interpret m2n wrapper if it is not found in aot image

On ios with interpreter enabled it can happen to mark an assembly as aot and have the rest interpreted, including SPC.dll. If the aot code attempts to do an icall, for example Math.Ceiling defined in SPC.dll, it will fail to find the m2n wrapper, since SPC.dll is not aot-ed. We fix this by obtaining an interp entry thunk, in order to execute the wrapper in interp, if we can't find the aot version of wrapper.

src/mono/mono/mini/interp/interp.c

@@ -3478,9 +3478,6 @@ interp_create_method_pointer (MonoMethod *method, gboolean compile, MonoError *e
 		return (gpointer)no_llvmonly_interp_method_pointer;
 	}
 
-	if (method->wrapper_type && method->wrapper_type == MONO_WRAPPER_MANAGED_TO_NATIVE)
-		return imethod;
-
 #ifndef MONO_ARCH_HAVE_FTNPTR_ARG_TRAMPOLINE
 	/*
 	 * Interp in wrappers get the argument in the rgctx register. If

src/mono/mono/mini/mini-runtime.c

@@ -2564,7 +2564,18 @@ compile_special (MonoMethod *method, MonoError *error)
 		} else {
 			MonoMethod *nm = mono_marshal_get_native_wrapper (method, TRUE, mono_aot_only);
 			compiled_method = mono_jit_compile_method_jit_only (nm, error);
-			return_val_if_nok (error, NULL);
+			if (!compiled_method && mono_aot_only && mono_use_interpreter) {
+				// We failed to find wrapper in aot images, try interpreting it instead
+				mono_error_cleanup (error);
+				error_init_reuse (error);
+				nm = mono_marshal_get_native_wrapper (method, TRUE, FALSE);
+				compiled_method = mono_jit_compile_method (nm, error);
+				return_val_if_nok (error, NULL);
+				code = mono_get_addr_from_ftnptr (compiled_method);
+				return code;
+			} else {
+				return_val_if_nok (error, NULL);
+			}
 		}
 
 		code = mono_get_addr_from_ftnptr (compiled_method);