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添加 Rust 语言圣经（镜像）
2 years ago
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<h1 id="miri"><a class="header" href="#miri">Miri</a></h1>
<p>看到这里，大家是不是暗中松了口气？unsafe 不过如此嘛，不知道为何其它人都谈之色变。</p>
<p>怎么说呢？你以为的编译器已经不是以前的编译器了，它不报错不代表没有错误。包括测试用例也是，正常地运行不能意味着代码没有任何错误。</p>
<p>在周星驰电影功夫中，还有一个奇怪大叔 10 元一本主动上门卖如来神掌，那么有没有 10 元一本的 Rust 秘笈呢？( 喂，Rust语言圣经都免费让你读了，有了摩托车，还要什么拖拉机... 哈哈，开个玩笑 )</p>
<p>有的，奇怪大叔正在赶来，他告诉我们先来安装一个命令:</p>
<pre><code class="language-shell">rustup +nightly-2022-01-21 component add miri
info: syncing channel updates for 'nightly-2022-01-21-x86_64-pc-windows-msvc'
info: latest update on 2022-01-21, rust version 1.60.0-nightly (777bb86bc 2022-01-20)
info: downloading component 'cargo'
info: downloading component 'clippy'
info: downloading component 'rust-docs'
info: downloading component 'rust-std'
info: downloading component 'rustc'
info: downloading component 'rustfmt'
info: installing component 'cargo'
info: installing component 'clippy'
info: installing component 'rust-docs'
info: installing component 'rust-std'
info: installing component 'rustc'
info: installing component 'rustfmt'
info: downloading component 'miri'
info: installing component 'miri'
</code></pre>
<p>等等，你在我电脑上装了什么奇怪的东西？！ &quot;好东西&quot;</p>
<blockquote>
<p>miri 目前只能在 nightly Rust 上安装，<code>+nightly-2022-01-21</code> 告诉 <code>rustup</code> 我们想要安装的 <code>nightly</code> 版本，事实上，你可以直接通过 <code>rustup +nightly component add miri</code> 安装，这里指定版本主要因为 <code>miri</code> 有时候会因为某些版本而出错。</p>
<p>2022-01-21 是我所知的 miri 可以成功运行的版本，你可以检查<a href="https://rust-lang.github.io/rustup-components-history/">这个网址</a>获取更多信息</p>
<ul>
<li>是一种临时性的规则运用，如果你不想每次都使用 <code>+nightly-2022-01-21</code>，可以使用 <a href="https://course.rs/appendix/rust-version.html#rustup-%E5%92%8C-rust-nightly-%E7%9A%84%E8%81%8C%E8%B4%A3"><code>rustup override set</code></a> 命令对当前项目的 Rust 版本进行覆盖</li>
</ul>
</blockquote>
<pre><code class="language-shell">$ cargo +nightly-2022-01-21 miri test
I will run `&quot;cargo.exe&quot; &quot;install&quot; &quot;xargo&quot;` to install
a recent enough xargo. Proceed? [Y/n]
</code></pre>
<p>额，<code>xargo</code> 是什么东东？&quot;不要担心，选择 y 就行，我像是会坑你的人吗？&quot;</p>
<pre><code class="language-shell">&gt; y
Updating crates.io index
Installing xargo v0.3.24
...
Finished release [optimized] target(s) in 10.65s
Installing C:\Users\ninte\.cargo\bin\xargo-check.exe
Installing C:\Users\ninte\.cargo\bin\xargo.exe
Installed package `xargo v0.3.24` (executables `xargo-check.exe`, `xargo.exe`)
I will run `&quot;rustup&quot; &quot;component&quot; &quot;add&quot; &quot;rust-src&quot;` to install
the `rust-src` component for the selected toolchain. Proceed? [Y/n]
</code></pre>
<p>额？ &quot;不要怕，多给你一份 Rust 源代码，不开心嘛？&quot;</p>
<pre><code class="language-shell">&gt; y
info: downloading component 'rust-src'
info: installing component 'rust-src'
</code></pre>
<p>&quot;看吧，我就说我不会骗你的，不相信我，等着错误砸脸吧!&quot; 真是一个奇怪的大叔...</p>
<pre><code class="language-shell"> Compiling lists v0.1.0 (C:\Users\ninte\dev\tmp\lists)
Finished test [unoptimized + debuginfo] target(s) in 0.25s
Running unittests (lists-5cc11d9ee5c3e924.exe)
error: Undefined Behavior: trying to reborrow for Unique at alloc84055,
but parent tag &lt;209678&gt; does not have an appropriate item in
the borrow stack
--&gt; \lib\rustlib\src\rust\library\core\src\option.rs:846:18
|
846 | Some(x) =&gt; Some(f(x)),
| ^ trying to reborrow for Unique at alloc84055,
| but parent tag &lt;209678&gt; does not have an
| appropriate item in the borrow stack
|
= help: this indicates a potential bug in the program:
it performed an invalid operation, but the rules it
violated are still experimental
= help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md
for further information
= note: inside `std::option::Option::&lt;std::boxed::Box&lt;fifth::Node&lt;i32&gt;&gt;&gt;::map::&lt;i32, [closure@src\fifth.rs:31:30: 40:10]&gt;` at \lib\rustlib\src\rust\library\core\src\option.rs:846:18
note: inside `fifth::List::&lt;i32&gt;::pop` at src\fifth.rs:31:9
--&gt; src\fifth.rs:31:9
|
31 | / self.head.take().map(|head| {
32 | | let head = *head;
33 | | self.head = head.next;
34 | |
... |
39 | | head.elem
40 | | })
| |__________^
note: inside `fifth::test::basics` at src\fifth.rs:74:20
--&gt; src\fifth.rs:74:20
|
74 | assert_eq!(list.pop(), Some(1));
| ^^^^^^^^^^
note: inside closure at src\fifth.rs:62:5
--&gt; src\fifth.rs:62:5
|
61 | #[test]
| ------- in this procedural macro expansion
62 | / fn basics() {
63 | | let mut list = List::new();
64 | |
65 | | // Check empty list behaves right
... |
96 | | assert_eq!(list.pop(), None);
97 | | }
| |_____^
...
error: aborting due to previous error
</code></pre>
<p>咦还真有错误，大叔，这是什么错误？大叔？...奇怪的大叔默默离开了，留下我在风中凌乱。</p>
<p>果然不靠谱...还是得靠自己，首先得了解下何为 <code>miri</code>。</p>
<p><a href="https://github.com/rust-lang/miri"><code>miri</code></a> 可以生成 Rust 的中间层表示 MIR，对于编译器来说，我们的 Rust 代码首先会被编译为 MIR ，然后再提交给 LLVM 进行处理。</p>
<p>可以通过 <code>rustup component add miri</code> 来安装它，并通过 <code>cargo miri</code> 来使用，同时还可以使用 <code>cargo miri test</code> 来运行测试代码。</p>
<p><code>miri</code> 可以帮助我们检查常见的未定义行为(UB = Undefined Behavior)，以下列出了一部分:</p>
<ul>
<li>内存越界检查和内存释放后再使用(use-after-free)</li>
<li>使用未初始化的数据</li>
<li>数据竞争</li>
<li>内存对齐问题</li>
</ul>
<p>UB 检测是必须的，因为它发生在运行时，因此很难发现，如果 <code>miri</code> 能在编译期检测出来，那自然是最好不过的。</p>
<p>总之，<code>miri</code> 的使用很简单:</p>
<pre><code class="language-shell">$ cargo +nightly-2022-01-21 miri test
</code></pre>
<p>下面来看看具体的错误：</p>
<pre><code class="language-shell">error: Undefined Behavior: trying to reborrow for Unique at alloc84055, but parent tag &lt;209678&gt; does not have an appropriate item in the borrow stack
--&gt; \lib\rustlib\src\rust\library\core\src\option.rs:846:18
|
846 | Some(x) =&gt; Some(f(x)),
| ^ trying to reborrow for Unique at alloc84055,
| but parent tag &lt;209678&gt; does not have an
| appropriate item in the borrow stack
|
= help: this indicates a potential bug in the program: it
performed an invalid operation, but the rules it
violated are still experimental
= help: see
https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md
for further information
</code></pre>
<p>嗯，只能看出是一个错误，其它完全看不懂了，例如什么是 <code>borrow stack</code>？</p>
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