From f3e9d066df50a6e77e8c15ea97b195a4b069f254 Mon Sep 17 00:00:00 2001
From: Chris Robinson <chris.kcat@gmail.com>
Date: Wed, 24 May 2023 11:56:56 -0700
Subject: Be a bit more safe with type mangling

---
 al/event.cpp       | 4 ++--
 alc/alu.cpp        | 6 ++----
 common/albit.h     | 7 ++++---
 core/async_event.h | 8 ++++++--
 core/context.cpp   | 6 ++++--
 core/voice.cpp     | 6 ++----
 6 files changed, 20 insertions(+), 17 deletions(-)

diff --git a/al/event.cpp b/al/event.cpp
index 7bd5ae1b..a5b5fdc5 100644
--- a/al/event.cpp
+++ b/al/event.cpp
@@ -56,7 +56,7 @@ int EventThread(ALCcontext *context)
 
         std::lock_guard<std::mutex> _{context->mEventCbLock};
         do {
-            auto *evt_ptr = reinterpret_cast<AsyncEvent*>(evt_data.buf);
+            auto *evt_ptr = std::launder(reinterpret_cast<AsyncEvent*>(evt_data.buf));
             evt_data.buf += sizeof(AsyncEvent);
             evt_data.len -= 1;
 
@@ -164,7 +164,7 @@ void StopEventThrd(ALCcontext *ctx)
             evt_data = ring->getWriteVector().first;
         } while(evt_data.len == 0);
     }
-    std::ignore = InitAsyncEvent<AsyncKillThread>(reinterpret_cast<AsyncEvent*>(evt_data.buf));
+    std::ignore = InitAsyncEvent<AsyncKillThread>(evt_data.buf);
     ring->writeAdvance(1);
 
     ctx->mEventSem.post();
diff --git a/alc/alu.cpp b/alc/alu.cpp
index cf250988..c43da639 100644
--- a/alc/alu.cpp
+++ b/alc/alu.cpp
@@ -491,8 +491,7 @@ bool CalcEffectSlotParams(EffectSlot *slot, EffectSlot **sorted_slots, ContextBa
         auto evt_vec = ring->getWriteVector();
         if(evt_vec.first.len > 0) LIKELY
         {
-            AsyncEffectReleaseEvent &evt = InitAsyncEvent<AsyncEffectReleaseEvent>(
-                reinterpret_cast<AsyncEvent*>(evt_vec.first.buf));
+            auto &evt = InitAsyncEvent<AsyncEffectReleaseEvent>(evt_vec.first.buf);
             evt.mEffectState = oldstate;
             ring->writeAdvance(1);
         }
@@ -1701,8 +1700,7 @@ void SendSourceStateEvent(ContextBase *context, uint id, VChangeState state)
     auto evt_vec = ring->getWriteVector();
     if(evt_vec.first.len < 1) return;
 
-    AsyncSourceStateEvent &evt = InitAsyncEvent<AsyncSourceStateEvent>(
-        reinterpret_cast<AsyncEvent*>(evt_vec.first.buf));
+    auto &evt = InitAsyncEvent<AsyncSourceStateEvent>(evt_vec.first.buf);
     evt.mId = id;
     switch(state)
     {
diff --git a/common/albit.h b/common/albit.h
index a563a4e7..962eb0aa 100644
--- a/common/albit.h
+++ b/common/albit.h
@@ -4,6 +4,7 @@
 #include <cstdint>
 #include <cstring>
 #include <limits>
+#include <new>
 #include <type_traits>
 #if !defined(__GNUC__) && (defined(_WIN32) || defined(_WIN64))
 #include <intrin.h>
@@ -16,9 +17,9 @@ std::enable_if_t<sizeof(To) == sizeof(From) && std::is_trivially_copyable_v<From
     && std::is_trivially_copyable_v<To>,
 To> bit_cast(const From &src) noexcept
 {
-    union { char c; To dst; } u;
-    std::memcpy(&u.dst, &src, sizeof(To));
-    return u.dst;
+    std::aligned_storage_t<sizeof(To), alignof(To)> dst;
+    std::memcpy(&dst, &src, sizeof(To));
+    return *std::launder(reinterpret_cast<To*>(&dst));
 }
 
 #ifdef __BYTE_ORDER__
diff --git a/core/async_event.h b/core/async_event.h
index 9e2d1193..c049fa02 100644
--- a/core/async_event.h
+++ b/core/async_event.h
@@ -54,7 +54,11 @@ using AsyncEvent = std::variant<AsyncKillThread,
         AsyncDisconnectEvent>;
 
 template<typename T, typename ...Args>
-auto &InitAsyncEvent(AsyncEvent *evt, Args&& ...args)
-{ return std::get<T>(*al::construct_at(evt, std::in_place_type<T>, std::forward<Args>(args)...)); }
+auto &InitAsyncEvent(std::byte *evtbuf, Args&& ...args)
+{
+    auto *evt = al::construct_at(reinterpret_cast<AsyncEvent*>(evtbuf), std::in_place_type<T>,
+        std::forward<Args>(args)...);
+    return std::get<T>(*evt);
+}
 
 #endif
diff --git a/core/context.cpp b/core/context.cpp
index 145ce349..2ebbc7b1 100644
--- a/core/context.cpp
+++ b/core/context.cpp
@@ -66,12 +66,14 @@ ContextBase::~ContextBase()
         auto evt_vec = mAsyncEvents->getReadVector();
         if(evt_vec.first.len > 0)
         {
-            std::destroy_n(reinterpret_cast<AsyncEvent*>(evt_vec.first.buf), evt_vec.first.len);
+            std::destroy_n(std::launder(reinterpret_cast<AsyncEvent*>(evt_vec.first.buf)),
+                evt_vec.first.len);
             count += evt_vec.first.len;
         }
         if(evt_vec.second.len > 0)
         {
-            std::destroy_n(reinterpret_cast<AsyncEvent*>(evt_vec.second.buf), evt_vec.second.len);
+            std::destroy_n(std::launder(reinterpret_cast<AsyncEvent*>(evt_vec.second.buf)),
+                evt_vec.second.len);
             count += evt_vec.second.len;
         }
         if(count > 0)
diff --git a/core/voice.cpp b/core/voice.cpp
index 3e78b176..65986cd1 100644
--- a/core/voice.cpp
+++ b/core/voice.cpp
@@ -226,8 +226,7 @@ void SendSourceStoppedEvent(ContextBase *context, uint id)
     auto evt_vec = ring->getWriteVector();
     if(evt_vec.first.len < 1) return;
 
-    AsyncSourceStateEvent &evt = InitAsyncEvent<AsyncSourceStateEvent>(
-        reinterpret_cast<AsyncEvent*>(evt_vec.first.buf));
+    auto &evt = InitAsyncEvent<AsyncSourceStateEvent>(evt_vec.first.buf);
     evt.mId = id;
     evt.mState = AsyncSrcState::Stop;
 
@@ -1151,8 +1150,7 @@ void Voice::mix(const State vstate, ContextBase *Context, const nanoseconds devi
         auto evt_vec = ring->getWriteVector();
         if(evt_vec.first.len > 0)
         {
-            AsyncBufferCompleteEvent &evt = InitAsyncEvent<AsyncBufferCompleteEvent>(
-                reinterpret_cast<AsyncEvent*>(evt_vec.first.buf));
+            auto &evt = InitAsyncEvent<AsyncBufferCompleteEvent>(evt_vec.first.buf);
             evt.mId = SourceID;
             evt.mCount = buffers_done;
             ring->writeAdvance(1);
-- 
cgit v1.2.3