[PATCH] score: More strict RTEMS_DEQUALIFY implementation.

[Pavel Pisa]

From: Pavel Pisa <pisa at cmp.felk.cvut.cz>
Subject: [PATCH] score: More strict RTEMS_DEQUALIFY implementation.

This implementation is able to catch cast to type
which differs not only in qualifiers. The error
diagnostic message when used in function is self
descriptive. Macro is compatible with used in initializers
but there message about not constant initial value
signals types incompatibility.

The actual implementation does not distinguish between
volatile and const removal.
---
 cpukit/score/include/rtems/score/basedefs.h | 54 ++++++++++++++++++++++++++++-
 1 file changed, 53 insertions(+), 1 deletion(-)

RTEMS build with macros succeed. It should have no influence on generated code
but check on produced binary level and code optimizations should check
that there is no GCC misbehave. __builtin_choose_expr has been problematic
on some ancient GCC version but it is used by Linux kernel now.
The use and even example with (void)0 is included/suggested by GCC
documentation. So I hope it is safe.

The actual implementation does not distinguish between
volatile and const removal. The original one could check
that probably for C++ case or with some specific GCC options.
But GCC with standard options does not inform about these partial
combinations. C++ const_cast removes both volatile and const as well.

diff --git a/cpukit/score/include/rtems/score/basedefs.h b/cpukit/score/include/rtems/score/basedefs.h
index 361f514..12480a8 100644
--- a/cpukit/score/include/rtems/score/basedefs.h
+++ b/cpukit/score/include/rtems/score/basedefs.h
@@ -191,7 +191,7 @@
  *  This can occur when reading volatile device memory or skipping arguments
  *  in a variable argument method.
  */
-#if defined(__GNUC__)        
+#if defined(__GNUC__)
   #define RTEMS_COMPILER_UNUSED_ATTRIBUTE __attribute__((unused))
 #else
   #define RTEMS_COMPILER_UNUSED_ATTRIBUTE
@@ -227,6 +227,39 @@
 #define RTEMS_CONTAINER_OF( _m, _type, _member_name ) \
   ( (_type *) ( (uintptr_t) ( _m ) - offsetof( _type, _member_name ) ) )
 
+#ifdef __cplusplus
+#define RTEMS_DEQUALIFY_DEPTHX( _ptr_level, _type, _var ) \
+            (const_cast<_type>( _var ))
+#else /* Standard C code */
+
+/* The reference type idea based on libHX by Jan Engelhardt */
+#define RTEMS_TYPEOF_REFX(_ptr_level, _ptr_type) \
+  typeof(_ptr_level(union { int z; typeof(_ptr_type) x; }){0}.x)
+
+#if defined(__GNUC__) && !defined(ASM)
+#if  ((__GNUC__ * 1000 + __GNUC_MINOR__) >= 4004)
+extern void* RTEMS_DEQUALIFY_types_not_compatible(void)
+  __attribute__((error ("RTEMS_DEQUALIFY types differ not only by volatile and const")));
+#else
+extern void RTEMS_DEQUALIFY_types_not_compatible(void);
+#endif
+#define RTEMS_DEQUALIFY_DEPTHX( _ptr_level, _type, _var ) ( \
+    __builtin_choose_expr( __builtin_types_compatible_p ( \
+        RTEMS_TYPEOF_REFX( _ptr_level, _var ), \
+        RTEMS_TYPEOF_REFX( _ptr_level, _type ) \
+      ) || __builtin_types_compatible_p ( _type, void * ), \
+    (_type)(_var), \
+    RTEMS_DEQUALIFY_types_not_compatible() \
+  ) \
+)
+#endif /*__GNUC__*/
+#endif /*__cplusplus*/
+
+#ifndef RTEMS_DECONST
+#ifdef RTEMS_DEQUALIFY_DEPTHX
+#define RTEMS_DECONST( _type, _var ) \
+  RTEMS_DEQUALIFY_DEPTHX( *, _type, _var )
+#else /*RTEMS_DEQUALIFY_DEPTHX*/
 /**
  * @brief Removes the const qualifier from a type of a variable.
  *
@@ -236,6 +269,14 @@
 #define RTEMS_DECONST( _type, _var ) \
   ((_type)(uintptr_t)(const void *) ( _var ))
 
+#endif /*RTEMS_DEQUALIFY_DEPTHX*/
+#endif /*RTEMS_DECONST*/
+
+#ifndef RTEMS_DEVOLATILE
+#ifdef RTEMS_DEQUALIFY_DEPTHX
+#define RTEMS_DEVOLATILE( _type, _var ) \
+  RTEMS_DEQUALIFY_DEPTHX( *, _type, _var )
+#else /*RTEMS_DEQUALIFY_DEPTHX*/
 /**
  * @brief Removes the volatile qualifier from a type of a variable.
  *
@@ -245,6 +286,14 @@
 #define RTEMS_DEVOLATILE( _type, _var ) \
   ((_type)(uintptr_t)(volatile void *) ( _var ))
 
+#endif /*RTEMS_DEQUALIFY_DEPTHX*/
+#endif /*RTEMS_DEVOLATILE*/
+
+#ifndef RTEMS_DEQUALIFY
+#ifdef RTEMS_DEQUALIFY_DEPTHX
+#define RTEMS_DEQUALIFY( _type, _var ) \
+  RTEMS_DEQUALIFY_DEPTHX( *, _type, _var )
+#else /*RTEMS_DEQUALIFY_DEPTHX*/
 /**
  * @brief Removes the all qualifiers from a type of a variable.
  *
@@ -254,6 +303,9 @@
 #define RTEMS_DEQUALIFY( _type, _var ) \
   ((_type)(uintptr_t)(const volatile void *) ( _var ))
 
+#endif /*RTEMS_DEQUALIFY_DEPTHX*/
+#endif /*RTEMS_DEQUALIFY*/
+
 #ifndef ASM
   #ifdef RTEMS_DEPRECATED_TYPES
     typedef bool boolean;
-- 
1.9.1