Merge pull request swiftlang#80516 from mikeash/function-cast

mikeash · web-flow · commit 433ca8ea8107 · 2025-04-11T05:15:25.000-04:00
[Runtime] Add function_cast, switch from std::bit_cast.
diff --git a/include/swift/Basic/Casting.h b/include/swift/Basic/Casting.h
@@ -0,0 +1,51 @@
+//===--- Casting.h - Helpers for casting ------------------------*- C++ -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2025 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SWIFT_BASIC_CASTING_H
+#define SWIFT_BASIC_CASTING_H
+
+#include <type_traits>
+
+namespace swift {
+
+/// Cast between two function types. Use in place of std::bit_cast, which
+/// doesn't work on ARM64e with address-discriminated signed function types.
+///
+/// Address-discriminated ptrauth attributes can only be applied to values with
+/// a defined storage location, such as struct fields, since their value is
+/// inherently tied to their address. They can't be applied to function
+/// paremeters. When passing such a value to a templated function, the ptrauth
+/// attribute disappears from the inferred type.
+///
+/// bit_cast takes the source by reference, which means that the ptrauth
+/// attribute remains on the inferred type, and the value is not trivially
+/// copyable.
+///
+/// function_cast instead takes the source by value, avoiding that issue and
+/// ensuring that passed-in function pointers are always trivially copyable.
+template <typename Destination, typename Source>
+Destination function_cast(Source source) {
+  static_assert(sizeof(Destination) == sizeof(Source),
+                "Source and destination must be the same size");
+  static_assert(std::is_trivially_copyable_v<Source>,
+                "The source type must be trivially constructible");
+  static_assert(std::is_trivially_copyable_v<Destination>,
+                "The destination type must be trivially constructible");
+
+  Destination destination;
+  memcpy(&destination, &source, sizeof(source));
+  return destination;
+}
+
+}
+
+#endif
diff --git a/include/swift/Runtime/STLCompatibility.h b/include/swift/Runtime/STLCompatibility.h
diff --git a/stdlib/public/Concurrency/AsyncLet.cpp b/stdlib/public/Concurrency/AsyncLet.cpp
@@ -24,9 +24,9 @@
 #include "swift/ABI/Metadata.h"
 #include "swift/ABI/Task.h"
 #include "swift/ABI/TaskOptions.h"
+#include "swift/Basic/Casting.h"
 #include "swift/Runtime/Heap.h"
 #include "swift/Runtime/HeapObject.h"
-#include "swift/Runtime/STLCompatibility.h"
 #include "swift/Threading/Mutex.h"
 #include "llvm/ADT/PointerIntPair.h"
 
@@ -289,7 +289,7 @@ static void _asyncLet_get_throwing_continuation(
 
   // Continue the caller's execution.
   auto throwingResume =
-      std::bit_cast<ThrowingTaskFutureWaitContinuationFunction*>(callContext->ResumeParent);
+      function_cast<ThrowingTaskFutureWaitContinuationFunction*>(callContext->ResumeParent);
   return throwingResume(callContext->Parent, error);
 }
 
@@ -307,7 +307,7 @@ static void swift_asyncLet_get_throwingImpl(
 
   auto aletContext = static_cast<AsyncLetContinuationContext*>(callContext);
   aletContext->ResumeParent =
-      std::bit_cast<TaskContinuationFunction*>(resumeFunction);
+      function_cast<TaskContinuationFunction*>(resumeFunction);
   aletContext->Parent = callerContext;
   aletContext->alet = alet;
   auto futureContext = asImpl(alet)->getFutureContext();
@@ -377,7 +377,7 @@ static void asyncLet_finish_after_task_completion(SWIFT_ASYNC_CONTEXT AsyncConte
     swift_task_dealloc(task);
   }
 
-  return std::bit_cast<ThrowingTaskFutureWaitContinuationFunction*>(resumeFunction)
+  return function_cast<ThrowingTaskFutureWaitContinuationFunction*>(resumeFunction)
     (callerContext, error);
 }
 
@@ -529,14 +529,14 @@ static void swift_asyncLet_consume_throwingImpl(
   if (asImpl(alet)->hasResultInBuffer()) {
     return asyncLet_finish_after_task_completion(callerContext,
                    alet,
-                   std::bit_cast<TaskContinuationFunction*>(resumeFunction),
+                   function_cast<TaskContinuationFunction*>(resumeFunction),
                    callContext,
                    nullptr);
   }
 
   auto aletContext = static_cast<AsyncLetContinuationContext*>(callContext);
   aletContext->ResumeParent =
-      std::bit_cast<TaskContinuationFunction*>(resumeFunction);
+      function_cast<TaskContinuationFunction*>(resumeFunction);
   aletContext->Parent = callerContext;
   aletContext->alet = alet;
   auto futureContext = asImpl(alet)->getFutureContext();
diff --git a/stdlib/public/Concurrency/DispatchGlobalExecutor.cpp b/stdlib/public/Concurrency/DispatchGlobalExecutor.cpp
@@ -30,9 +30,9 @@
 
 #include <cstddef>
 
+#include "swift/Basic/Casting.h"
 #include "swift/Runtime/Concurrency.h"
 #include "swift/Runtime/EnvironmentVariables.h"
-#include "swift/Runtime/STLCompatibility.h"
 
 #if SWIFT_CONCURRENCY_ENABLE_DISPATCH
 #include "swift/Runtime/HeapObject.h"
@@ -99,11 +99,11 @@ static void initializeDispatchEnqueueFunc(dispatch_queue_t queue, void *obj,
   if (SWIFT_RUNTIME_WEAK_CHECK(dispatch_async_swift_job))
     func = SWIFT_RUNTIME_WEAK_USE(dispatch_async_swift_job);
 #elif defined(_WIN32)
-  func = std::bit_cast<dispatchEnqueueFuncType>(
+  func = function_cast<dispatchEnqueueFuncType>(
       GetProcAddress(LoadLibraryW(L"dispatch.dll"),
       "dispatch_async_swift_job"));
 #else
-  func = std::bit_cast<dispatchEnqueueFuncType>(
+  func = function_cast<dispatchEnqueueFuncType>(
       dlsym(RTLD_NEXT, "dispatch_async_swift_job"));
 #endif
 #endif
diff --git a/stdlib/public/Concurrency/Task.cpp b/stdlib/public/Concurrency/Task.cpp
@@ -30,6 +30,7 @@
 #include "swift/ABI/Metadata.h"
 #include "swift/ABI/Task.h"
 #include "swift/ABI/TaskOptions.h"
+#include "swift/Basic/Casting.h"
 #include "swift/Basic/Lazy.h"
 #include "swift/Runtime/Concurrency.h"
 #include "swift/Runtime/EnvironmentVariables.h"
@@ -1075,19 +1076,19 @@ swift_task_create_commonImpl(size_t rawTaskCreateFlags,
   // The final funclet shouldn't release the task or the task function.
   } else if (asyncLet) {
     initialContext->ResumeParent =
-      reinterpret_cast<TaskContinuationFunction*>(&completeTask);
+        function_cast<TaskContinuationFunction *>(&completeTask);
 
   // If we have a non-null closure context and the task function is not
   // consumed by calling it, use a final funclet that releases both the
   // task and the closure context.
   } else if (closureContext && !taskCreateFlags.isTaskFunctionConsumed()) {
     initialContext->ResumeParent =
-      reinterpret_cast<TaskContinuationFunction*>(&completeTaskWithClosure);
+        function_cast<TaskContinuationFunction *>(&completeTaskWithClosure);
 
   // Otherwise, just release the task.
   } else {
     initialContext->ResumeParent =
-      reinterpret_cast<TaskContinuationFunction*>(&completeTaskAndRelease);
+        function_cast<TaskContinuationFunction *>(&completeTaskAndRelease);
   }
 #pragma clang diagnostic pop
 
diff --git a/stdlib/public/Concurrency/TaskGroup.cpp b/stdlib/public/Concurrency/TaskGroup.cpp
@@ -27,13 +27,13 @@
 #include "swift/ABI/Task.h"
 #include "swift/ABI/TaskGroup.h"
 #include "swift/ABI/TaskOptions.h"
+#include "swift/Basic/Casting.h"
 #include "swift/Basic/RelativePointer.h"
 #include "swift/Basic/STLExtras.h"
 #include "swift/Runtime/Concurrency.h"
 #include "swift/Runtime/Config.h"
 #include "swift/Runtime/Heap.h"
 #include "swift/Runtime/HeapObject.h"
-#include "swift/Runtime/STLCompatibility.h"
 #include "swift/Threading/Mutex.h"
 #include <atomic>
 #include <deque>
@@ -1661,7 +1661,7 @@ task_group_wait_resume_adapter(SWIFT_ASYNC_CONTEXT AsyncContext *_context) {
 
   auto context = static_cast<TaskFutureWaitAsyncContext *>(_context);
   auto resumeWithError =
-      std::bit_cast<AsyncVoidClosureResumeEntryPoint *>(context->ResumeParent);
+      function_cast<AsyncVoidClosureResumeEntryPoint *>(context->ResumeParent);
   return resumeWithError(context->Parent, context->errorResult);
 }
 
@@ -1713,7 +1713,7 @@ static void swift_taskGroup_wait_next_throwingImpl(
 
   auto context = static_cast<TaskFutureWaitAsyncContext *>(rawContext);
   context->ResumeParent =
-      std::bit_cast<TaskContinuationFunction *>(resumeFunction);
+      function_cast<TaskContinuationFunction *>(resumeFunction);
   context->Parent = callerContext;
   context->errorResult = nullptr;
   context->successResultPointer = resultPointer;
@@ -1945,7 +1945,7 @@ void TaskGroupBase::waitAll(SwiftError* bodyError, AsyncTask *waitingTask,
 
   auto context = static_cast<TaskFutureWaitAsyncContext *>(rawContext);
   context->ResumeParent =
-      std::bit_cast<TaskContinuationFunction *>(resumeFunction);
+      function_cast<TaskContinuationFunction *>(resumeFunction);
   context->Parent = callerContext;
   context->errorResult = nullptr;
   context->successResultPointer = resultPointer;
diff --git a/stdlib/public/Distributed/DistributedActor.cpp b/stdlib/public/Distributed/DistributedActor.cpp
@@ -17,9 +17,9 @@
 #include "swift/ABI/Actor.h"
 #include "swift/ABI/Metadata.h"
 #include "swift/ABI/Task.h"
+#include "swift/Basic/Casting.h"
 #include "swift/Runtime/AccessibleFunction.h"
 #include "swift/Runtime/Concurrency.h"
-#include "swift/Runtime/STLCompatibility.h"
 
 using namespace swift;
 
@@ -103,7 +103,7 @@ static void swift_distributed_execute_target_resume(
     SWIFT_CONTEXT SwiftError *error) {
   auto parentCtx = context->Parent;
   auto resumeInParent =
-      std::bit_cast<TargetExecutorSignature::ContinuationType *>(
+      function_cast<TargetExecutorSignature::ContinuationType *>(
           parentCtx->ResumeParent);
   swift_task_dealloc(context);
   // See `swift_distributed_execute_target` - `parentCtx` in this case
@@ -132,7 +132,7 @@ void swift_distributed_execute_target(
     SwiftError *error =
         swift_distributed_makeDistributedTargetAccessorNotFoundError();
     auto resumeInParent =
-        std::bit_cast<TargetExecutorSignature::ContinuationType *>(
+        function_cast<TargetExecutorSignature::ContinuationType *>(
             callerContext->ResumeParent);
     resumeInParent(callerContext, error);
     return;
@@ -150,7 +150,7 @@ void swift_distributed_execute_target(
       swift_task_alloc(asyncFnPtr->ExpectedContextSize));
 
   calleeContext->Parent = callerContext;
-  calleeContext->ResumeParent = std::bit_cast<TaskContinuationFunction *>(
+  calleeContext->ResumeParent = function_cast<TaskContinuationFunction *>(
       &swift_distributed_execute_target_resume);
 
   accessorEntry(calleeContext, argumentDecoder, argumentTypes, resultBuffer,
diff --git a/test/embedded/dependencies-concurrency-custom-executor.swift b/test/embedded/dependencies-concurrency-custom-executor.swift
@@ -18,6 +18,7 @@
 // DEP: _exit
 // DEP: _free
 // DEP: _malloc
+// DEP: _memcpy
 // DEP: _memmove
 // DEP: _memset
 // DEP: _memset_s
diff --git a/test/embedded/dependencies-concurrency.swift b/test/embedded/dependencies-concurrency.swift
@@ -18,6 +18,7 @@
 // DEP: _exit
 // DEP: _free
 // DEP: _malloc
+// DEP: _memcpy
 // DEP: _memmove
 // DEP: _memset
 // DEP: _memset_s
diff --git a/test/embedded/dependencies-concurrency2.swift b/test/embedded/dependencies-concurrency2.swift
@@ -16,6 +16,7 @@
 // DEP: _exit
 // DEP: _free
 // DEP: _malloc
+// DEP: _memcpy
 // DEP: _memmove
 // DEP: _memset
 // DEP: _memset_s
