[lldb] Eliminate SupportFileSP nullptr derefs #168624
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| Original file line number | Diff line number | Diff line change |
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| //===----------------------------------------------------------------------===// | ||
| // | ||
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. | ||
| // See https://llvm.org/LICENSE.txt for license information. | ||
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception | ||
| // | ||
| //===----------------------------------------------------------------------===// | ||
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| #ifndef LLDB_UTILITY_NONNULLSHAREDPTR_H | ||
| #define LLDB_UTILITY_NONNULLSHAREDPTR_H | ||
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| #include <memory> | ||
| #include <utility> | ||
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| namespace lldb_private { | ||
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| /// A non-nullable shared pointer that always holds a valid object. | ||
| /// | ||
| /// NonNullSharedPtr is a smart pointer wrapper around std::shared_ptr that | ||
| /// guarantees the pointer is never null. If default-constructed, it creates | ||
| /// a default-constructed instance of T. | ||
| /// | ||
| /// This class is used for enforcing invariants at the type level and | ||
| /// eliminating entire classes of null pointer bugs. | ||
| /// | ||
| /// @tparam T The type of object to manage. Must be default-constructible. | ||
| template <typename T> class NonNullSharedPtr : private std::shared_ptr<T> { | ||
| using Base = std::shared_ptr<T>; | ||
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| public: | ||
| NonNullSharedPtr() : Base(std::make_shared<T>()) {} | ||
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| NonNullSharedPtr(const std::shared_ptr<T> &t) | ||
| : Base(t ? t : std::make_shared<T>()) { | ||
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Contributor
There was a problem hiding this comment. why do you want to support calling this class with nullptrs? Based on my "will this compile" question below, I suspect we really don't want |
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| assert(t && "NonNullSharedPtr initialized from NULL shared_ptr"); | ||
| } | ||
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| NonNullSharedPtr(std::shared_ptr<T> &&t) | ||
| : Base(t ? std::move(t) : std::make_shared<T>()) { | ||
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Contributor
There was a problem hiding this comment. does this compile for types that cannot be default constructed? Also, I think here you can just make a helper function that asserts and returns. |
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| // Can't assert on t as it's been moved-from. | ||
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Member
There was a problem hiding this comment. You can't assert on t, but you can assert that you're non-null, right?
Member
Author
There was a problem hiding this comment. Yes, but that could only happen if
Contributor
There was a problem hiding this comment. Given the LineTableTest path, which would silently create an empty object, should we instead unconditionally move t in Not sure if this snippet works |
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| } | ||
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| NonNullSharedPtr(const NonNullSharedPtr &other) : Base(other) {} | ||
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| NonNullSharedPtr(NonNullSharedPtr &&other) noexcept | ||
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| : Base(std::move(other)) {} | ||
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| NonNullSharedPtr &operator=(const NonNullSharedPtr &other) { | ||
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Contributor
There was a problem hiding this comment. is this different from |
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| Base::operator=(other); | ||
| return *this; | ||
| } | ||
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| NonNullSharedPtr &operator=(NonNullSharedPtr &&other) noexcept { | ||
| Base::operator=(std::move(other)); | ||
| return *this; | ||
| } | ||
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| using Base::operator*; | ||
| using Base::operator->; | ||
| using Base::get; | ||
| using Base::unique; | ||
| using Base::use_count; | ||
| using Base::operator bool; | ||
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| void swap(NonNullSharedPtr &other) noexcept { Base::swap(other); } | ||
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| /// Explicitly deleted operations that could introduce nullptr. | ||
| /// @{ | ||
| void reset() = delete; | ||
| void reset(T *ptr) = delete; | ||
| /// @} | ||
| }; | ||
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| } // namespace lldb_private | ||
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| template <typename T> | ||
| bool operator==(const lldb_private::NonNullSharedPtr<T> &lhs, | ||
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| const lldb_private::NonNullSharedPtr<T> &rhs) { | ||
| return lhs.get() == rhs.get(); | ||
| } | ||
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| template <typename T> | ||
| bool operator!=(const lldb_private::NonNullSharedPtr<T> &lhs, | ||
| const lldb_private::NonNullSharedPtr<T> &rhs) { | ||
| return !(lhs == rhs); | ||
| } | ||
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| /// Specialized swap function for NonNullSharedPtr to enable argument-dependent | ||
| /// lookup (ADL) and efficient swapping. | ||
| template <typename T> | ||
| void swap(lldb_private::NonNullSharedPtr<T> &lhs, | ||
| lldb_private::NonNullSharedPtr<T> &rhs) noexcept { | ||
| lhs.swap(rhs); | ||
| } | ||
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| #endif | ||
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Should this assert that
make_sharedsucceeded in creating a non-nullshared_ptr? It's rare but we have exceptions disabled, so this will violate the invariant under your nose and you'll crash somewhere later on anyway.There was a problem hiding this comment.
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I don't mind adding it, but at the same time, if malloc failed, we have bigger issues, and nothing in LLDB is resilient against that... so it would just be theater.
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I merged the PR but happy to revisit this post-commit if you disagree with my conclusion.