From a8e336c2b57ff1e38f2a511aab8c2c6060c1796d Mon Sep 17 00:00:00 2001
From: Simon Marchi <simon.marchi@efficios.com>
Date: Wed, 8 Sep 2021 18:00:42 -0400
Subject: [PATCH] common: prevent using memset on non-POD types
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While converting some code to use C++ constructs, it can be easy to
forget to change some spot that uses memset to initialize or move the
object. Add a templated deleted declaration to prevent using memset on
types that aren't POD.

For example, if I make lttng_ust_event non-POD, in
src/bin/lttng-sessiond/trace-ust.h, I get this error:

      CXX      save.lo
    /home/simark/src/lttng-tools/src/bin/lttng-sessiond/save.cpp: In function ‘int save_agent_events(config_writer*, agent*)’:
    /home/simark/src/lttng-tools/src/bin/lttng-sessiond/save.cpp:1246:23: error: use of deleted function ‘void* memset(T*, int, size_t) [with T = ltt_ust_event; <template-parameter-1-2> = void; size_t = long unsigned int]’
     1246 |                 memset(&fake_event, 0, sizeof(fake_event));
          |                 ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    In file included from /home/simark/src/lttng-tools/src/common/defaults.h:14,
                     from /home/simark/src/lttng-tools/src/bin/lttng-sessiond/save.cpp:15:
    /home/simark/src/lttng-tools/src/common/macros.h:128:7: note: declared here
      128 | void *memset(T *s, int c, size_t n) = delete;
          |       ^~~~~~

Note: I tried applying this to memcpy as well, but Clang gave me some
troubles with its -Waddress-of-packed-member diagnostic, so I gave up.

Change-Id: Id55735db15901c6fc5d58e9b6b6b689733302398
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
---
 src/common/macros.hpp | 37 ++++++++++++++++++++++++++++++++++---
 1 file changed, 34 insertions(+), 3 deletions(-)

diff --git a/src/common/macros.hpp b/src/common/macros.hpp
index 49f163b42..b734652ee 100644
--- a/src/common/macros.hpp
+++ b/src/common/macros.hpp
@@ -136,14 +136,45 @@ T *malloc(size_t size)
  */
 
 template<typename T>
-struct is_pod_or_void
+struct can_free
 {
-	static constexpr bool value = std::is_pod<T>::value || std::is_void<T>::value;
+	static constexpr bool value = std::is_trivially_destructible<T>::value || std::is_void<T>::value;
 };
 
-template<typename T, typename = typename std::enable_if<!is_pod_or_void<T>::value>::type>
+template<typename T, typename = typename std::enable_if<!can_free<T>::value>::type>
 void free(T *p) = delete;
 
+template<typename T>
+struct can_memset
+{
+	static constexpr bool value = std::is_pod<T>::value || std::is_void<T>::value;
+};
+
+template <typename T, typename = typename std::enable_if<!can_memset<T>::value>::type>
+void *memset(T *s, int c, size_t n) = delete;
+
+template<typename T>
+struct can_memcpy
+{
+	static constexpr bool value = std::is_trivially_copyable<T>::value;
+};
+
+template <typename T, typename U,
+		typename = typename std::enable_if<!can_memcpy<T>::value>::type,
+		typename = typename std::enable_if<!can_memcpy<U>::value>::type>
+void *memcpy(T *d, const U *s, size_t n) = delete;
+
+template<typename T>
+struct can_memmove
+{
+	static constexpr bool value = std::is_trivially_copyable<T>::value;
+};
+
+template <typename T, typename U,
+		typename = typename std::enable_if<!can_memmove<T>::value>::type,
+		typename = typename std::enable_if<!can_memmove<U>::value>::type>
+void *memmove(T *d, const U *s, size_t n) = delete;
+
 #ifndef ARRAY_SIZE
 #define ARRAY_SIZE(array)   (sizeof(array) / (sizeof((array)[0])))
 #endif
-- 
2.34.1