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When SWIFT_COMPACT_ABSOLUTE_FUNCTION_POINTER is enabled, relative direct pointers whose pointees are functions will be turned into absolute pointer at compile-time.
63 lines
2.3 KiB
C++
63 lines
2.3 KiB
C++
//===--- CompactFunctionPointer.h - Compact Function Pointers ---*- C++ -*-===//
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//
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// This source file is part of the Swift.org open source project
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//
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// Copyright (c) 2014 - 2022 Apple Inc. and the Swift project authors
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// Licensed under Apache License v2.0 with Runtime Library Exception
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//
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// See https://swift.org/LICENSE.txt for license information
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// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
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//
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//===----------------------------------------------------------------------===//
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//
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// Swift's runtime structures often use relative function pointers to reduce the
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// size of metadata and also to minimize load-time overhead in PIC.
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// This file defines pointer types whose size and interface are compatible with
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// the relative pointer types for targets that do not support relative references
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// to code from data.
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//===----------------------------------------------------------------------===//
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#ifndef SWIFT_ABI_COMPACTFUNCTIONPOINTER_H
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#define SWIFT_ABI_COMPACTFUNCTIONPOINTER_H
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namespace swift {
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/// A compact unconditional absolute function pointer that can fit in a 32-bit
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/// integer.
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/// As a trade-off compared to relative pointers, this has load-time overhead in PIC
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/// and is only available on 32-bit targets.
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template <typename T>
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class AbsoluteFunctionPointer {
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T *Pointer;
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static_assert(sizeof(T *) == sizeof(int32_t),
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"Function pointer must be 32-bit when using compact absolute pointer");
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public:
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using PointerTy = T *;
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PointerTy get() const & { return Pointer; }
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operator PointerTy() const & { return this->get(); }
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bool isNull() const & { return Pointer == nullptr; }
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/// Resolve a pointer from a `base` pointer and a value loaded from `base`.
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template <typename BasePtrTy, typename Value>
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static PointerTy resolve(BasePtrTy *base, Value value) {
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return reinterpret_cast<PointerTy>(value);
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}
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template <typename... ArgTy>
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typename std::result_of<T *(ArgTy...)>::type operator()(ArgTy... arg) const {
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static_assert(std::is_function<T>::value,
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"T must be an explicit function type");
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return this->get()(std::forward<ArgTy>(arg)...);
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}
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};
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// TODO(katei): Add another pointer structure for 64-bit targets and for efficiency on PIC
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} // namespace swift
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#endif // SWIFT_ABI_COMPACTFUNCTIONPOINTER_H
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