[PATCH 4/4] Poison XNEW and friends for types that should use new/delete

[Simon Marchi <simon.marchi@ericsson.com>]

From: Simon Marchi <simon.marchi@polymtl.ca>

This patch (finally!) makes it so that trying to use XNEW with a type
that requires "new" will cause a compilation error.  The criterion I
initially used to allow a type to use XNEW (which calls malloc in the
end) was std::is_trivially_constructible, but then realized that gcc 4.8
did not have it.  Instead, I went with:

  using IsMallocatable = std::is_pod<T>;

which is just a bit more strict, which doesn't hurt.  A similar thing is
done for macros that free instead of allocated, the criterion is:

  using IsFreeable = gdb::Or<std::is_trivially_destructible<T>, std::is_void<T>>;

For simplicity, we could also do for std::is_pod for IsFreeable as well,
if you prefer.

I chose to put static_assert in the functions, instead of using
gdb::Requires in the template as SFINAE, because it allows to put a
message, which I think makes the compiler error more understandable.
With gdb::Requires, the error is:

    In file included from /home/simark/src/binutils-gdb/gdb/common/common-utils.h:26:0,
                     from /home/simark/src/binutils-gdb/gdb/common/common-defs.h:78,
                     from /home/simark/src/binutils-gdb/gdb/defs.h:28,
                     from /home/simark/src/binutils-gdb/gdb/lala.c:1:
    /home/simark/src/binutils-gdb/gdb/lala.c: In function ‘void foo()’:
    /home/simark/src/binutils-gdb/gdb/common/poison.h:108:25: error: no matching function for call to ‘xnew<bar>()’
     #define XNEW(T) xnew<T>()
                             ^
    /home/simark/src/binutils-gdb/gdb/lala.c:13:3: note: in expansion of macro ‘XNEW’
       XNEW(bar);
       ^~~~
    /home/simark/src/binutils-gdb/gdb/common/poison.h:101:1: note: candidate: template<class T, typename std::enable_if<std::is_trivially_constructible<_Tp>::value, void>::type <anonymous> > T* xnew()
     xnew ()
     ^~~~
    /home/simark/src/binutils-gdb/gdb/common/poison.h:101:1: note:   template argument deduction/substitution failed:
    /home/simark/src/binutils-gdb/gdb/common/poison.h:108:25: note:   couldn't deduce template parameter ‘<anonymous>’
     #define XNEW(T) xnew<T>()
                             ^
    /home/simark/src/binutils-gdb/gdb/lala.c:13:3: note: in expansion of macro ‘XNEW’
       XNEW(bar);
       ^~~~

and with static_assert:

    In file included from /home/simark/src/binutils-gdb/gdb/common/common-utils.h:26:0,
                     from /home/simark/src/binutils-gdb/gdb/common/common-defs.h:78,
                     from /home/simark/src/binutils-gdb/gdb/defs.h:28,
                     from /home/simark/src/binutils-gdb/gdb/lala.c:1:
    /home/simark/src/binutils-gdb/gdb/common/poison.h: In instantiation of ‘T* xnew() [with T = bar]’:
    /home/simark/src/binutils-gdb/gdb/lala.c:13:3:   required from here
    /home/simark/src/binutils-gdb/gdb/common/poison.h:103:3: error: static assertion failed: Trying to use XNEW with a non-POD data type.  Use operator new instead.
       static_assert (IsMallocatable<T>::value, "Trying to use XNEW with a non-POD\
       ^~~~~~~~~~~~~

I think the first one is more likely to just make people yell at their
screen, especially those less used to C++.

Generated-code-wise, it adds one more function call (xnew<T>) when using
XNEW and building with -O0, but it all goes away with optimizations
enabled.

gdb/ChangeLog:

	* common/common-utils.h: Include poison.h.
	(xfree): Remove declaration, add definition with static_assert.
	* common/common-utils.c (xfree): Remove.
	* common/poison.h (IsMallocatable): Define.
	(IsFreeable): Define.
	(free): Delete for non-freeable types.
	(xnew): New.
	(XNEW): Undef and redefine.
	(xcnew): New.
	(XCNEW): Undef and redefine.
	(xdelete): New.
	(XDELETE): Undef and redefine.
	(xnewvec): New.
	(XNEWVEC): Undef and redefine.
	(xcnewvec): New.
	(XCNEWVEC): Undef and redefine.
	(xresizevec): New.
	(XRESIZEVEC): Undef and redefine.
	(xdeletevec): New.
	(XDELETEVEC): Undef and redefine.
	(xnewvar): New.
	(XNEWVAR): Undef and redefine.
	(xcnewvar): New.
	(XCNEWVAR): Undef and redefine.
	(xresizevar): New.
	(XRESIZEVAR): Undef and redefine.
---
 gdb/common/common-utils.c |   7 ---
 gdb/common/common-utils.h |  14 ++++-
 gdb/common/poison.h       | 132 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 145 insertions(+), 8 deletions(-)

diff --git a/gdb/common/common-utils.c b/gdb/common/common-utils.c
index 7139302..66d6161 100644
--- a/gdb/common/common-utils.c
+++ b/gdb/common/common-utils.c
@@ -95,13 +95,6 @@ xzalloc (size_t size)
 }
 
 void
-xfree (void *ptr)
-{
-  if (ptr != NULL)
-    free (ptr);		/* ARI: free */
-}
-
-void
 xmalloc_failed (size_t size)
 {
   malloc_failure (size);
diff --git a/gdb/common/common-utils.h b/gdb/common/common-utils.h
index 4926a32..feb4790 100644
--- a/gdb/common/common-utils.h
+++ b/gdb/common/common-utils.h
@@ -23,6 +23,8 @@
 #include <string>
 #include <vector>
 
+#include "poison.h"
+
 /* If possible, define FUNCTION_NAME, a macro containing the name of
    the function being defined.  Since this macro may not always be
    defined, all uses must be protected by appropriate macro definition
@@ -47,7 +49,17 @@
 /* Like xmalloc, but zero the memory.  */
 void *xzalloc (size_t);
 
-void xfree (void *);
+template <typename T>
+static void
+xfree (T *ptr)
+{
+  static_assert (IsFreeable<T>::value, "Trying to use xfree with a non-POD \
+data type.  Use operator delete instead.");
+
+  if (ptr != NULL)
+    free (ptr);		/* ARI: free */
+}
+
 
 /* Like asprintf and vasprintf, but return the string, throw an error
    if no memory.  */
diff --git a/gdb/common/poison.h b/gdb/common/poison.h
index 37dd35e..de4cefa 100644
--- a/gdb/common/poison.h
+++ b/gdb/common/poison.h
@@ -84,4 +84,136 @@ void *memmove (D *dest, const S *src, size_t n) = delete;
 
 #endif /* HAVE_IS_TRIVIALLY_COPYABLE */
 
+/* Poison XNEW and friends to catch usages of malloc-style allocations on
+   objects that require new/delete.  */
+
+template<typename T>
+using IsMallocatable = std::is_pod<T>;
+
+template<typename T>
+using IsFreeable = gdb::Or<std::is_trivially_destructible<T>, std::is_void<T>>;
+
+template <typename T, typename = gdb::Requires<gdb::Not<IsFreeable<T>>>>
+void free (T *ptr) = delete;
+
+template<typename T>
+static T *
+xnew ()
+{
+  static_assert (IsMallocatable<T>::value, "Trying to use XNEW with a non-POD \
+data type.  Use operator new instead.");
+  return XNEW (T);
+}
+
+#undef XNEW
+#define XNEW(T) xnew<T>()
+
+template<typename T>
+static T *
+xcnew ()
+{
+  static_assert (IsMallocatable<T>::value, "Trying to use XCNEW with a non-POD \
+data type.  Use operator new instead.");
+  return XCNEW (T);
+}
+
+#undef XCNEW
+#define XCNEW(T) xcnew<T>()
+
+template<typename T>
+static void
+xdelete (T *p)
+{
+  static_assert (IsFreeable<T>::value, "Trying to use XDELETE with a non-POD \
+data type.  Use operator delete instead.");
+  XDELETE (p);
+}
+
+#undef XDELETE
+#define XDELETE(P) xdelete (p)
+
+template<typename T>
+static T*
+xnewvec (size_t n)
+{
+  static_assert (IsMallocatable<T>::value, "Trying to use XNEWVEC with a \
+non-POD data type.  Use operator new[] (or std::vector) instead.");
+  return XNEWVEC (T, n);
+}
+
+#undef XNEWVEC
+#define XNEWVEC(T, N) xnewvec<T> (N)
+
+template<typename T>
+static T*
+xcnewvec (size_t n)
+{
+  static_assert (IsMallocatable<T>::value, "Trying to use XCNEWVEC with a \
+non-POD data type.  Use operator new[] (or std::vector) instead.");
+  return XCNEWVEC (T, n);
+}
+
+#undef XCNEWVEC
+#define XCNEWVEC(T, N) xcnewvec<T> (N)
+
+template<typename T>
+static T*
+xresizevec (T *p, size_t n)
+{
+  static_assert (IsMallocatable<T>::value, "Trying to use XRESIZEVEC with a \
+non-POD data type.");
+  return XRESIZEVEC (T, p, n);
+}
+
+#undef XRESIZEVEC
+#define XRESIZEVEC(T, P, N) xresizevec<T> (P, N)
+
+template<typename T>
+static void
+xdeletevec (T *p)
+{
+  static_assert (IsFreeable<T>::value, "Trying to use XDELETEVEC with a \
+non-POD data type.  Use operator delete[] (or std::vector) instead.");
+  XDELETEVEC (p);
+}
+
+#undef XDELETEVEC
+#define XDELETEVEC(P) xdeletevec (P)
+
+template<typename T>
+static T*
+xnewvar (size_t s)
+{
+  static_assert (IsMallocatable<T>::value, "Trying to use XNEWVAR with a \
+non-POD data type.");
+  return XNEWVAR (T, s);;
+}
+
+#undef XNEWVAR
+#define XNEWVAR(T, S) xnewvar<T> (S)
+
+template<typename T>
+static T*
+xcnewvar (size_t s)
+{
+  static_assert (IsMallocatable<T>::value, "Trying to use XCNEWVAR with a \
+non-POD data type.");
+  return XCNEWVAR (T, s);
+}
+
+#undef XCNEWVAR
+#define XCNEWVAR(T, S) xcnewvar<T> (S)
+
+template<typename T>
+static T*
+xresizevar (T *p, size_t s)
+{
+  static_assert (IsMallocatable<T>::value, "Trying to use XRESIZEVAR with a \
+non-POD data type.");
+  return XRESIZEVAR (T, p, s);
+}
+
+#undef XRESIZEVAR
+#define XRESIZEVAR(T, P, S) xresizevar<T> (P, S)
+
 #endif /* COMMON_POISON_H */
-- 
2.7.4