检测到临时的悬挂引用 [英] Detect dangling references to temporary

问题描述

Clang 3.9非常重用临时用户使用的内存。

Clang 3.9 extremely reuses memory used by temporaries.

此代码为UB（简化代码）：

This code is UB (simplified code):

template <class T>
class my_optional
{
public:
    bool has{ false };
    T value;

    const T& get_or_default(const T& def)
    {
        return has ? value : def;
    }
};

void use(const std::string& s)
{
    // ...
}

int main()
{
    my_optional<std::string> m;
    // ...
    const std::string& s = m.get_or_default("default value");
    use(s); // s is dangling if default returned
}

我们有大量类似上面的代码（ my_optional 只是一个简单的示例来说明它。）

We have tons of code something like above (my_optional is just a simple example to illustrate it).

由于UB从3.9开始，所有clang编译器重用此内存，这是合法行为。

Because of UB all clang compiler since 3.9 starts to reuse this memory, and it is lawful behavior.

问题是：如何在编译时或使用消毒剂之类的检测此类悬挂引用在运行时？没有clang消毒剂可以检测到它们。

The question is: how to detect such dangling references at compile time or with something like sanitizer at runtime? No clang sanitizer can detect them.

已更新。请不要回答：使用 std :: optional 。请仔细阅读：问题不在于此。

Upd2。请不要回答：您的代码设计不好。仔细阅读：问题与代码设计无关。

Upd. Please do not answer: "use std::optional". Read carefully: question is NOT about it.
Upd2. Please do not answer: "your code design is bad". Read carefully: question is NOT about code design.

推荐答案

您可以通过添加额外的重载来检测对该特定API的滥用：

You can detect misuses of this particular API by adding an additional overload:

const T& get_or_default(T&& rvalue) = delete;

如果给 get_or_default 的自变量是真正的右值，将选择它，因此编译将失败。

If the argument given to get_or_default is a true rvalue, it will be chosen instead, so compilation will fail.

关于在运行时检测此类错误，请尝试使用Clang的AddressSanitizer和use-after-return（ ASAN_OPTIONS = detect_stack_use_after_return = 1 ）和/或范围后使用（ -fsanitize-address-use-after-scope ）检测已启用。

As for detecting such errors at runtime, try using Clang's AddressSanitizer with use-after-return (ASAN_OPTIONS=detect_stack_use_after_return=1) and/or use-after-scope (-fsanitize-address-use-after-scope) detection enabled.

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