| <!DOCTYPE HTML> |
| <html lang="en" class="light sidebar-visible" dir="ltr"> |
| <head> |
| <!-- Book generated using mdBook --> |
| <meta charset="UTF-8"> |
| <title>Panicking - The Embedded Rust Book</title> |
| |
| |
| <!-- Custom HTML head --> |
| |
| <meta name="description" content=""> |
| <meta name="viewport" content="width=device-width, initial-scale=1"> |
| <meta name="theme-color" content="#ffffff"> |
| |
| <link rel="icon" href="../favicon.svg"> |
| <link rel="shortcut icon" href="../favicon.png"> |
| <link rel="stylesheet" href="../css/variables.css"> |
| <link rel="stylesheet" href="../css/general.css"> |
| <link rel="stylesheet" href="../css/chrome.css"> |
| <link rel="stylesheet" href="../css/print.css" media="print"> |
| |
| <!-- Fonts --> |
| <link rel="stylesheet" href="../FontAwesome/css/font-awesome.css"> |
| <link rel="stylesheet" href="../fonts/fonts.css"> |
| |
| <!-- Highlight.js Stylesheets --> |
| <link rel="stylesheet" id="highlight-css" href="../highlight.css"> |
| <link rel="stylesheet" id="tomorrow-night-css" href="../tomorrow-night.css"> |
| <link rel="stylesheet" id="ayu-highlight-css" href="../ayu-highlight.css"> |
| |
| <!-- Custom theme stylesheets --> |
| |
| |
| <!-- Provide site root and default themes to javascript --> |
| <script> |
| const path_to_root = "../"; |
| const default_light_theme = "light"; |
| const default_dark_theme = "navy"; |
| </script> |
| <!-- Start loading toc.js asap --> |
| <script src="../toc.js"></script> |
| </head> |
| <body> |
| <div id="mdbook-help-container"> |
| <div id="mdbook-help-popup"> |
| <h2 class="mdbook-help-title">Keyboard shortcuts</h2> |
| <div> |
| <p>Press <kbd>←</kbd> or <kbd>→</kbd> to navigate between chapters</p> |
| <p>Press <kbd>S</kbd> or <kbd>/</kbd> to search in the book</p> |
| <p>Press <kbd>?</kbd> to show this help</p> |
| <p>Press <kbd>Esc</kbd> to hide this help</p> |
| </div> |
| </div> |
| </div> |
| <div id="body-container"> |
| <!-- Work around some values being stored in localStorage wrapped in quotes --> |
| <script> |
| try { |
| let theme = localStorage.getItem('mdbook-theme'); |
| let sidebar = localStorage.getItem('mdbook-sidebar'); |
| |
| if (theme.startsWith('"') && theme.endsWith('"')) { |
| localStorage.setItem('mdbook-theme', theme.slice(1, theme.length - 1)); |
| } |
| |
| if (sidebar.startsWith('"') && sidebar.endsWith('"')) { |
| localStorage.setItem('mdbook-sidebar', sidebar.slice(1, sidebar.length - 1)); |
| } |
| } catch (e) { } |
| </script> |
| |
| <!-- Set the theme before any content is loaded, prevents flash --> |
| <script> |
| const default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? default_dark_theme : default_light_theme; |
| let theme; |
| try { theme = localStorage.getItem('mdbook-theme'); } catch(e) { } |
| if (theme === null || theme === undefined) { theme = default_theme; } |
| const html = document.documentElement; |
| html.classList.remove('light') |
| html.classList.add(theme); |
| html.classList.add("js"); |
| </script> |
| |
| <input type="checkbox" id="sidebar-toggle-anchor" class="hidden"> |
| |
| <!-- Hide / unhide sidebar before it is displayed --> |
| <script> |
| let sidebar = null; |
| const sidebar_toggle = document.getElementById("sidebar-toggle-anchor"); |
| if (document.body.clientWidth >= 1080) { |
| try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { } |
| sidebar = sidebar || 'visible'; |
| } else { |
| sidebar = 'hidden'; |
| } |
| sidebar_toggle.checked = sidebar === 'visible'; |
| html.classList.remove('sidebar-visible'); |
| html.classList.add("sidebar-" + sidebar); |
| </script> |
| |
| <nav id="sidebar" class="sidebar" aria-label="Table of contents"> |
| <!-- populated by js --> |
| <mdbook-sidebar-scrollbox class="sidebar-scrollbox"></mdbook-sidebar-scrollbox> |
| <noscript> |
| <iframe class="sidebar-iframe-outer" src="../toc.html"></iframe> |
| </noscript> |
| <div id="sidebar-resize-handle" class="sidebar-resize-handle"> |
| <div class="sidebar-resize-indicator"></div> |
| </div> |
| </nav> |
| |
| <div id="page-wrapper" class="page-wrapper"> |
| |
| <div class="page"> |
| <div id="menu-bar-hover-placeholder"></div> |
| <div id="menu-bar" class="menu-bar sticky"> |
| <div class="left-buttons"> |
| <label id="sidebar-toggle" class="icon-button" for="sidebar-toggle-anchor" title="Toggle Table of Contents" aria-label="Toggle Table of Contents" aria-controls="sidebar"> |
| <i class="fa fa-bars"></i> |
| </label> |
| <button id="theme-toggle" class="icon-button" type="button" title="Change theme" aria-label="Change theme" aria-haspopup="true" aria-expanded="false" aria-controls="theme-list"> |
| <i class="fa fa-paint-brush"></i> |
| </button> |
| <ul id="theme-list" class="theme-popup" aria-label="Themes" role="menu"> |
| <li role="none"><button role="menuitem" class="theme" id="default_theme">Auto</button></li> |
| <li role="none"><button role="menuitem" class="theme" id="light">Light</button></li> |
| <li role="none"><button role="menuitem" class="theme" id="rust">Rust</button></li> |
| <li role="none"><button role="menuitem" class="theme" id="coal">Coal</button></li> |
| <li role="none"><button role="menuitem" class="theme" id="navy">Navy</button></li> |
| <li role="none"><button role="menuitem" class="theme" id="ayu">Ayu</button></li> |
| </ul> |
| <button id="search-toggle" class="icon-button" type="button" title="Search (`/`)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="/ s" aria-controls="searchbar"> |
| <i class="fa fa-search"></i> |
| </button> |
| </div> |
| |
| <h1 class="menu-title">The Embedded Rust Book</h1> |
| |
| <div class="right-buttons"> |
| <a href="../print.html" title="Print this book" aria-label="Print this book"> |
| <i id="print-button" class="fa fa-print"></i> |
| </a> |
| <a href="https://github.com/rust-embedded/book" title="Git repository" aria-label="Git repository"> |
| <i id="git-repository-button" class="fa fa-github"></i> |
| </a> |
| |
| </div> |
| </div> |
| |
| <div id="search-wrapper" class="hidden"> |
| <form id="searchbar-outer" class="searchbar-outer"> |
| <input type="search" id="searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="searchresults-outer" aria-describedby="searchresults-header"> |
| </form> |
| <div id="searchresults-outer" class="searchresults-outer hidden"> |
| <div id="searchresults-header" class="searchresults-header"></div> |
| <ul id="searchresults"> |
| </ul> |
| </div> |
| </div> |
| |
| <!-- Apply ARIA attributes after the sidebar and the sidebar toggle button are added to the DOM --> |
| <script> |
| document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible'); |
| document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible'); |
| Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) { |
| link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1); |
| }); |
| </script> |
| |
| <div id="content" class="content"> |
| <main> |
| <h1 id="panicking"><a class="header" href="#panicking">Panicking</a></h1> |
| <p>Panicking is a core part of the Rust language. Built-in operations like indexing |
| are runtime checked for memory safety. When out of bounds indexing is attempted |
| this results in a panic.</p> |
| <p>In the standard library panicking has a defined behavior: it unwinds the stack |
| of the panicking thread, unless the user opted for aborting the program on |
| panics.</p> |
| <p>In programs without standard library, however, the panicking behavior is left |
| undefined. A behavior can be chosen by declaring a <code>#[panic_handler]</code> function. |
| This function must appear exactly <em>once</em> in the dependency graph of a program, |
| and must have the following signature: <code>fn(&PanicInfo) -> !</code>, where <a href="https://doc.rust-lang.org/core/panic/struct.PanicInfo.html"><code>PanicInfo</code></a> |
| is a struct containing information about the location of the panic.</p> |
| <p>Given that embedded systems range from user facing to safety critical (cannot |
| crash) there's no one size fits all panicking behavior but there are plenty of |
| commonly used behaviors. These common behaviors have been packaged into crates |
| that define the <code>#[panic_handler]</code> function. Some examples include:</p> |
| <ul> |
| <li><a href="https://crates.io/crates/panic-abort"><code>panic-abort</code></a>. A panic causes the abort instruction to be executed.</li> |
| <li><a href="https://crates.io/crates/panic-halt"><code>panic-halt</code></a>. A panic causes the program, or the current thread, to halt by |
| entering an infinite loop.</li> |
| <li><a href="https://crates.io/crates/panic-itm"><code>panic-itm</code></a>. The panicking message is logged using the ITM, an ARM Cortex-M |
| specific peripheral.</li> |
| <li><a href="https://crates.io/crates/panic-semihosting"><code>panic-semihosting</code></a>. The panicking message is logged to the host using the |
| semihosting technique.</li> |
| </ul> |
| <p>You may be able to find even more crates searching for the <a href="https://crates.io/keywords/panic-handler"><code>panic-handler</code></a> |
| keyword on crates.io.</p> |
| <p>A program can pick one of these behaviors simply by linking to the corresponding |
| crate. The fact that the panicking behavior is expressed in the source of |
| an application as a single line of code is not only useful as documentation but |
| can also be used to change the panicking behavior according to the compilation |
| profile. For example:</p> |
| <pre><code class="language-rust ignore">#![no_main] |
| #![no_std] |
| |
| // dev profile: easier to debug panics; can put a breakpoint on `rust_begin_unwind` |
| #[cfg(debug_assertions)] |
| use panic_halt as _; |
| |
| // release profile: minimize the binary size of the application |
| #[cfg(not(debug_assertions))] |
| use panic_abort as _; |
| |
| // ..</code></pre> |
| <p>In this example the crate links to the <code>panic-halt</code> crate when built with the |
| dev profile (<code>cargo build</code>), but links to the <code>panic-abort</code> crate when built |
| with the release profile (<code>cargo build --release</code>).</p> |
| <blockquote> |
| <p>The <code>use panic_abort as _;</code> form of the <code>use</code> statement is used to ensure the <code>panic_abort</code> panic handler is |
| included in our final executable while making it clear to the compiler that we won't explicitly use anything from |
| the crate. Without the <code>as _</code> rename, the compiler would warn that we have an unused import. |
| Sometimes you might see <code>extern crate panic_abort</code> instead, which is an older style used before the |
| 2018 edition of Rust, and should now only be used for "sysroot" crates (those distributed with Rust itself) such |
| as <code>proc_macro</code>, <code>alloc</code>, <code>std</code>, and <code>test</code>.</p> |
| </blockquote> |
| <h2 id="an-example"><a class="header" href="#an-example">An example</a></h2> |
| <p>Here's an example that tries to index an array beyond its length. The operation |
| results in a panic.</p> |
| <pre><code class="language-rust ignore">#![no_main] |
| #![no_std] |
| |
| use panic_semihosting as _; |
| |
| use cortex_m_rt::entry; |
| |
| #[entry] |
| fn main() -> ! { |
| let xs = [0, 1, 2]; |
| let i = xs.len(); |
| let _y = xs[i]; // out of bounds access |
| |
| loop {} |
| }</code></pre> |
| <p>This example chose the <code>panic-semihosting</code> behavior which prints the panic |
| message to the host console using semihosting.</p> |
| <pre><code class="language-text">$ cargo run |
| Running `qemu-system-arm -cpu cortex-m3 -machine lm3s6965evb (..) |
| panicked at 'index out of bounds: the len is 3 but the index is 4', src/main.rs:12:13 |
| </code></pre> |
| <p>You can try changing the behavior to <code>panic-halt</code> and confirm that no message is |
| printed in that case.</p> |
| |
| </main> |
| |
| <nav class="nav-wrapper" aria-label="Page navigation"> |
| <!-- Mobile navigation buttons --> |
| <a rel="prev" href="../start/semihosting.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left"> |
| <i class="fa fa-angle-left"></i> |
| </a> |
| |
| <a rel="next prefetch" href="../start/exceptions.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right"> |
| <i class="fa fa-angle-right"></i> |
| </a> |
| |
| <div style="clear: both"></div> |
| </nav> |
| </div> |
| </div> |
| |
| <nav class="nav-wide-wrapper" aria-label="Page navigation"> |
| <a rel="prev" href="../start/semihosting.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left"> |
| <i class="fa fa-angle-left"></i> |
| </a> |
| |
| <a rel="next prefetch" href="../start/exceptions.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right"> |
| <i class="fa fa-angle-right"></i> |
| </a> |
| </nav> |
| |
| </div> |
| |
| |
| |
| |
| <script> |
| window.playground_copyable = true; |
| </script> |
| |
| |
| <script src="../elasticlunr.min.js"></script> |
| <script src="../mark.min.js"></script> |
| <script src="../searcher.js"></script> |
| |
| <script src="../clipboard.min.js"></script> |
| <script src="../highlight.js"></script> |
| <script src="../book.js"></script> |
| |
| <!-- Custom JS scripts --> |
| |
| |
| </div> |
| </body> |
| </html> |
