Add stub implementation for MPS tracing API

MPS' tracing module uses four macros:

1) TRACE( type, fmt, ... )

   This acts like `printf( fmt, ... )` but also allows
   the specification of a type of trace output (comment,
   warning, error, ...)

2) TRACE_INIT

   This acts like TRACE() but increases the level of
   indentation. It will be used at the beginning of
   function calls.

3) RETURN( val )

   Equivalent to `return( val )` plus a decrement in the
   level of indentation. This should be used at the end of
   functions that have been started with TRACE_INIT.

4) TRACE_END

   This combines a trace output with a decrement of the
   level of indentation. It's necessary prior to leaving
   functions which have been started with TRACE_INIT
   but which don't have a return value.

This commit defines those macros as no-op dummies in
`library/mps/trace.h` for now.

Signed-off-by: Hanno Becker <hanno.becker@arm.com>

library/mps/common.h

@@ -48,7 +48,7 @@
 #define MBEDTLS_MPS_ENABLE_ASSERTIONS
 
 /*! This flag controls whether tracing for MPS should be enabled. */
-#define MBEDTLS_MPS_TRACE
+//#define MBEDTLS_MPS_TRACE
 
 /* \} name SECTION: MPS Configuration */
 

library/mps/trace.h

@@ -0,0 +1,45 @@
+/*
+ *  Copyright The Mbed TLS Contributors
+ *  SPDX-License-Identifier: Apache-2.0
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License"); you may
+ *  not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ *  This file is part of mbed TLS (https://tls.mbed.org)
+ */
+
+/**
+ * \file trace.h
+ *
+ * \brief Tracing module for MPS
+ */
+
+#ifndef MBEDTLS_MPS_TRACE_H
+#define MBEDTLS_MPS_TRACE_H
+
+#include "common.h"
+
+#if defined(MBEDTLS_MPS_TRACE)
+
+#error "MPS tracing module not yet implemented"
+
+#else /* MBEDTLS_MPS_TRACE */
+
+#define TRACE( type, fmt, ... ) do { } while( 0 )
+#define TRACE_INIT( fmt, ... )  do { } while( 0 )
+#define TRACE_END               do { } while( 0 )
+
+#define RETURN( val ) return( val );
+
+#endif /* MBEDTLS_MPS_TRACE */
+
+#endif /* MBEDTLS_MPS_TRACE_H */