| <!DOCTYPE HTML> |
| <html lang="en" class="light sidebar-visible" dir="ltr"> |
| <head> |
| <!-- Book generated using mdBook --> |
| <meta charset="UTF-8"> |
| <title>QEMU - 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="qemu"><a class="header" href="#qemu">QEMU</a></h1> |
| <p>We'll start writing a program for the <a href="http://www.ti.com/product/LM3S6965">LM3S6965</a>, a Cortex-M3 microcontroller. |
| We have chosen this as our initial target because it <a href="https://wiki.qemu.org/Documentation/Platforms/ARM#Supported_in_qemu-system-arm">can be emulated</a> using QEMU |
| so you don't need to fiddle with hardware in this section and we can focus on |
| the tooling and the development process.</p> |
| <p><strong>IMPORTANT</strong> |
| We'll use the name "app" for the project name in this tutorial. |
| Whenever you see the word "app" you should replace it with the name you selected |
| for your project. Or, you could also name your project "app" and avoid the |
| substitutions.</p> |
| <h2 id="creating-a-non-standard-rust-program"><a class="header" href="#creating-a-non-standard-rust-program">Creating a non standard Rust program</a></h2> |
| <p>We'll use the <a href="https://github.com/rust-embedded/cortex-m-quickstart"><code>cortex-m-quickstart</code></a> project template to generate a new |
| project from it. The created project will contain a barebone application: a good |
| starting point for a new embedded rust application. In addition, the project will |
| contain an <code>examples</code> directory, with several separate applications, highlighting |
| some of the key embedded rust functionality.</p> |
| <h3 id="using-cargo-generate"><a class="header" href="#using-cargo-generate">Using <code>cargo-generate</code></a></h3> |
| <p>First install cargo-generate</p> |
| <pre><code class="language-console">cargo install cargo-generate |
| </code></pre> |
| <p>Then generate a new project</p> |
| <pre><code class="language-console">cargo generate --git https://github.com/rust-embedded/cortex-m-quickstart |
| </code></pre> |
| <pre><code class="language-text"> Project Name: app |
| Creating project called `app`... |
| Done! New project created /tmp/app |
| </code></pre> |
| <pre><code class="language-console">cd app |
| </code></pre> |
| <h3 id="using-git"><a class="header" href="#using-git">Using <code>git</code></a></h3> |
| <p>Clone the repository</p> |
| <pre><code class="language-console">git clone https://github.com/rust-embedded/cortex-m-quickstart app |
| cd app |
| </code></pre> |
| <p>And then fill in the placeholders in the <code>Cargo.toml</code> file</p> |
| <pre><code class="language-toml">[package] |
| authors = ["{{authors}}"] # "{{authors}}" -> "John Smith" |
| edition = "2018" |
| name = "{{project-name}}" # "{{project-name}}" -> "app" |
| version = "0.1.0" |
| |
| # .. |
| |
| [[bin]] |
| name = "{{project-name}}" # "{{project-name}}" -> "app" |
| test = false |
| bench = false |
| </code></pre> |
| <h3 id="using-neither"><a class="header" href="#using-neither">Using neither</a></h3> |
| <p>Grab the latest snapshot of the <code>cortex-m-quickstart</code> template and extract it.</p> |
| <pre><code class="language-console">curl -LO https://github.com/rust-embedded/cortex-m-quickstart/archive/master.zip |
| unzip master.zip |
| mv cortex-m-quickstart-master app |
| cd app |
| </code></pre> |
| <p>Or you can browse to <a href="https://github.com/rust-embedded/cortex-m-quickstart"><code>cortex-m-quickstart</code></a>, click the green "Clone or |
| download" button and then click "Download ZIP".</p> |
| <p>Then fill in the placeholders in the <code>Cargo.toml</code> file as done in the second |
| part of the "Using <code>git</code>" version.</p> |
| <h2 id="program-overview"><a class="header" href="#program-overview">Program Overview</a></h2> |
| <p>For convenience here are the most important parts of the source code in <code>src/main.rs</code>:</p> |
| <pre><code class="language-rust ignore">#![no_std] |
| #![no_main] |
| |
| use panic_halt as _; |
| |
| use cortex_m_rt::entry; |
| |
| #[entry] |
| fn main() -> ! { |
| loop { |
| // your code goes here |
| } |
| }</code></pre> |
| <p>This program is a bit different from a standard Rust program so let's take a |
| closer look.</p> |
| <p><code>#![no_std]</code> indicates that this program will <em>not</em> link to the standard crate, |
| <code>std</code>. Instead it will link to its subset: the <code>core</code> crate.</p> |
| <p><code>#![no_main]</code> indicates that this program won't use the standard <code>main</code> |
| interface that most Rust programs use. The main (no pun intended) reason to go |
| with <code>no_main</code> is that using the <code>main</code> interface in <code>no_std</code> context requires |
| nightly.</p> |
| <p><code>use panic_halt as _;</code>. This crate provides a <code>panic_handler</code> that defines |
| the panicking behavior of the program. We will cover this in more detail in the |
| <a href="panicking.html">Panicking</a> chapter of the book.</p> |
| <p><a href="https://docs.rs/cortex-m-rt-macros/latest/cortex_m_rt_macros/attr.entry.html"><code>#[entry]</code></a> is an attribute provided by the <a href="https://crates.io/crates/cortex-m-rt"><code>cortex-m-rt</code></a> crate that's used |
| to mark the entry point of the program. As we are not using the standard <code>main</code> |
| interface we need another way to indicate the entry point of the program and |
| that'd be <code>#[entry]</code>.</p> |
| <p><code>fn main() -> !</code>. Our program will be the <em>only</em> process running on the target |
| hardware so we don't want it to end! We use a <a href="https://doc.rust-lang.org/rust-by-example/fn/diverging.html">divergent function</a> (the <code>-> !</code> |
| bit in the function signature) to ensure at compile time that'll be the case.</p> |
| <h2 id="cross-compiling"><a class="header" href="#cross-compiling">Cross compiling</a></h2> |
| <p>The next step is to <em>cross</em> compile the program for the Cortex-M3 architecture. |
| That's as simple as running <code>cargo build --target $TRIPLE</code> if you know what the |
| compilation target (<code>$TRIPLE</code>) should be. Luckily, the <code>.cargo/config.toml</code> in the |
| template has the answer:</p> |
| <pre><code class="language-console">tail -n6 .cargo/config.toml |
| </code></pre> |
| <pre><code class="language-toml">[build] |
| # Pick ONE of these compilation targets |
| # target = "thumbv6m-none-eabi" # Cortex-M0 and Cortex-M0+ |
| target = "thumbv7m-none-eabi" # Cortex-M3 |
| # target = "thumbv7em-none-eabi" # Cortex-M4 and Cortex-M7 (no FPU) |
| # target = "thumbv7em-none-eabihf" # Cortex-M4F and Cortex-M7F (with FPU) |
| </code></pre> |
| <p>To cross compile for the Cortex-M3 architecture we have to use |
| <code>thumbv7m-none-eabi</code>. That target is not automatically installed when installing |
| the Rust toolchain, it would now be a good time to add that target to the toolchain, |
| if you haven't done it yet:</p> |
| <pre><code class="language-console">rustup target add thumbv7m-none-eabi |
| </code></pre> |
| <p>Since the <code>thumbv7m-none-eabi</code> compilation target has been set as the default in |
| your <code>.cargo/config.toml</code> file, the two commands below do the same:</p> |
| <pre><code class="language-console">cargo build --target thumbv7m-none-eabi |
| cargo build |
| </code></pre> |
| <h2 id="inspecting"><a class="header" href="#inspecting">Inspecting</a></h2> |
| <p>Now we have a non-native ELF binary in <code>target/thumbv7m-none-eabi/debug/app</code>. We |
| can inspect it using <code>cargo-binutils</code>.</p> |
| <p>With <code>cargo-readobj</code> we can print the ELF headers to confirm that this is an ARM |
| binary.</p> |
| <pre><code class="language-console">cargo readobj --bin app -- --file-headers |
| </code></pre> |
| <p>Note that:</p> |
| <ul> |
| <li><code>--bin app</code> is sugar for inspect the binary at <code>target/$TRIPLE/debug/app</code></li> |
| <li><code>--bin app</code> will also (re)compile the binary, if necessary</li> |
| </ul> |
| <pre><code class="language-text">ELF Header: |
| Magic: 7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 |
| Class: ELF32 |
| Data: 2's complement, little endian |
| Version: 1 (current) |
| OS/ABI: UNIX - System V |
| ABI Version: 0x0 |
| Type: EXEC (Executable file) |
| Machine: ARM |
| Version: 0x1 |
| Entry point address: 0x405 |
| Start of program headers: 52 (bytes into file) |
| Start of section headers: 153204 (bytes into file) |
| Flags: 0x5000200 |
| Size of this header: 52 (bytes) |
| Size of program headers: 32 (bytes) |
| Number of program headers: 2 |
| Size of section headers: 40 (bytes) |
| Number of section headers: 19 |
| Section header string table index: 18 |
| </code></pre> |
| <p><code>cargo-size</code> can print the size of the linker sections of the binary.</p> |
| <pre><code class="language-console">cargo size --bin app --release -- -A |
| </code></pre> |
| <p>we use <code>--release</code> to inspect the optimized version</p> |
| <pre><code class="language-text">app : |
| section size addr |
| .vector_table 1024 0x0 |
| .text 92 0x400 |
| .rodata 0 0x45c |
| .data 0 0x20000000 |
| .bss 0 0x20000000 |
| .debug_str 2958 0x0 |
| .debug_loc 19 0x0 |
| .debug_abbrev 567 0x0 |
| .debug_info 4929 0x0 |
| .debug_ranges 40 0x0 |
| .debug_macinfo 1 0x0 |
| .debug_pubnames 2035 0x0 |
| .debug_pubtypes 1892 0x0 |
| .ARM.attributes 46 0x0 |
| .debug_frame 100 0x0 |
| .debug_line 867 0x0 |
| Total 14570 |
| </code></pre> |
| <blockquote> |
| <p>A refresher on ELF linker sections</p> |
| <ul> |
| <li><code>.text</code> contains the program instructions</li> |
| <li><code>.rodata</code> contains constant values like strings</li> |
| <li><code>.data</code> contains statically allocated variables whose initial values are |
| <em>not</em> zero</li> |
| <li><code>.bss</code> also contains statically allocated variables whose initial values |
| <em>are</em> zero</li> |
| <li><code>.vector_table</code> is a <em>non</em>-standard section that we use to store the vector |
| (interrupt) table</li> |
| <li><code>.ARM.attributes</code> and the <code>.debug_*</code> sections contain metadata and will |
| <em>not</em> be loaded onto the target when flashing the binary.</li> |
| </ul> |
| </blockquote> |
| <p><strong>IMPORTANT</strong>: ELF files contain metadata like debug information so their <em>size |
| on disk</em> does <em>not</em> accurately reflect the space the program will occupy when |
| flashed on a device. <em>Always</em> use <code>cargo-size</code> to check how big a binary really |
| is.</p> |
| <p><code>cargo-objdump</code> can be used to disassemble the binary.</p> |
| <pre><code class="language-console">cargo objdump --bin app --release -- --disassemble --no-show-raw-insn --print-imm-hex |
| </code></pre> |
| <blockquote> |
| <p><strong>NOTE</strong> if the above command complains about <code>Unknown command line argument</code> see |
| the following bug report: https://github.com/rust-embedded/book/issues/269</p> |
| </blockquote> |
| <blockquote> |
| <p><strong>NOTE</strong> this output can differ on your system. New versions of rustc, LLVM |
| and libraries can generate different assembly. We truncated some of the instructions |
| to keep the snippet small.</p> |
| </blockquote> |
| <pre><code class="language-text">app: file format ELF32-arm-little |
| |
| Disassembly of section .text: |
| main: |
| 400: bl #0x256 |
| 404: b #-0x4 <main+0x4> |
| |
| Reset: |
| 406: bl #0x24e |
| 40a: movw r0, #0x0 |
| < .. truncated any more instructions .. > |
| |
| DefaultHandler_: |
| 656: b #-0x4 <DefaultHandler_> |
| |
| UsageFault: |
| 657: strb r7, [r4, #0x3] |
| |
| DefaultPreInit: |
| 658: bx lr |
| |
| __pre_init: |
| 659: strb r7, [r0, #0x1] |
| |
| __nop: |
| 65a: bx lr |
| |
| HardFaultTrampoline: |
| 65c: mrs r0, msp |
| 660: b #-0x2 <HardFault_> |
| |
| HardFault_: |
| 662: b #-0x4 <HardFault_> |
| |
| HardFault: |
| 663: <unknown> |
| </code></pre> |
| <h2 id="running"><a class="header" href="#running">Running</a></h2> |
| <p>Next, let's see how to run an embedded program on QEMU! This time we'll use the |
| <code>hello</code> example which actually does something.</p> |
| <p>For convenience here's the source code of <code>examples/hello.rs</code>:</p> |
| <pre><code class="language-rust ignore">//! Prints "Hello, world!" on the host console using semihosting |
| |
| #![no_main] |
| #![no_std] |
| |
| use panic_halt as _; |
| |
| use cortex_m_rt::entry; |
| use cortex_m_semihosting::{debug, hprintln}; |
| |
| #[entry] |
| fn main() -> ! { |
| hprintln!("Hello, world!").unwrap(); |
| |
| // exit QEMU |
| // NOTE do not run this on hardware; it can corrupt OpenOCD state |
| debug::exit(debug::EXIT_SUCCESS); |
| |
| loop {} |
| }</code></pre> |
| <p>This program uses something called semihosting to print text to the <em>host</em> |
| console. When using real hardware this requires a debug session but when using |
| QEMU this Just Works.</p> |
| <p>Let's start by compiling the example:</p> |
| <pre><code class="language-console">cargo build --example hello |
| </code></pre> |
| <p>The output binary will be located at |
| <code>target/thumbv7m-none-eabi/debug/examples/hello</code>.</p> |
| <p>To run this binary on QEMU run the following command:</p> |
| <pre><code class="language-console">qemu-system-arm \ |
| -cpu cortex-m3 \ |
| -machine lm3s6965evb \ |
| -nographic \ |
| -semihosting-config enable=on,target=native \ |
| -kernel target/thumbv7m-none-eabi/debug/examples/hello |
| </code></pre> |
| <pre><code class="language-text">Hello, world! |
| </code></pre> |
| <p>The command should successfully exit (exit code = 0) after printing the text. On |
| *nix you can check that with the following command:</p> |
| <pre><code class="language-console">echo $? |
| </code></pre> |
| <pre><code class="language-text">0 |
| </code></pre> |
| <p>Let's break down that QEMU command:</p> |
| <ul> |
| <li> |
| <p><code>qemu-system-arm</code>. This is the QEMU emulator. There are a few variants of |
| these QEMU binaries; this one does full <em>system</em> emulation of <em>ARM</em> machines |
| hence the name.</p> |
| </li> |
| <li> |
| <p><code>-cpu cortex-m3</code>. This tells QEMU to emulate a Cortex-M3 CPU. Specifying the |
| CPU model lets us catch some miscompilation errors: for example, running a |
| program compiled for the Cortex-M4F, which has a hardware FPU, will make QEMU |
| error during its execution.</p> |
| </li> |
| <li> |
| <p><code>-machine lm3s6965evb</code>. This tells QEMU to emulate the LM3S6965EVB, an |
| evaluation board that contains a LM3S6965 microcontroller.</p> |
| </li> |
| <li> |
| <p><code>-nographic</code>. This tells QEMU to not launch its GUI.</p> |
| </li> |
| <li> |
| <p><code>-semihosting-config (..)</code>. This tells QEMU to enable semihosting. Semihosting |
| lets the emulated device, among other things, use the host stdout, stderr and |
| stdin and create files on the host.</p> |
| </li> |
| <li> |
| <p><code>-kernel $file</code>. This tells QEMU which binary to load and run on the emulated |
| machine.</p> |
| </li> |
| </ul> |
| <p>Typing out that long QEMU command is too much work! We can set a custom runner |
| to simplify the process. <code>.cargo/config.toml</code> has a commented out runner that invokes |
| QEMU; let's uncomment it:</p> |
| <pre><code class="language-console">head -n3 .cargo/config.toml |
| </code></pre> |
| <pre><code class="language-toml">[target.thumbv7m-none-eabi] |
| # uncomment this to make `cargo run` execute programs on QEMU |
| runner = "qemu-system-arm -cpu cortex-m3 -machine lm3s6965evb -nographic -semihosting-config enable=on,target=native -kernel" |
| </code></pre> |
| <p>This runner only applies to the <code>thumbv7m-none-eabi</code> target, which is our |
| default compilation target. Now <code>cargo run</code> will compile the program and run it |
| on QEMU:</p> |
| <pre><code class="language-console">cargo run --example hello --release |
| </code></pre> |
| <pre><code class="language-text"> Compiling app v0.1.0 (file:///tmp/app) |
| Finished release [optimized + debuginfo] target(s) in 0.26s |
| Running `qemu-system-arm -cpu cortex-m3 -machine lm3s6965evb -nographic -semihosting-config enable=on,target=native -kernel target/thumbv7m-none-eabi/release/examples/hello` |
| Hello, world! |
| </code></pre> |
| <h2 id="debugging"><a class="header" href="#debugging">Debugging</a></h2> |
| <p>Debugging is critical to embedded development. Let's see how it's done.</p> |
| <p>Debugging an embedded device involves <em>remote</em> debugging as the program that we |
| want to debug won't be running on the machine that's running the debugger |
| program (GDB or LLDB).</p> |
| <p>Remote debugging involves a client and a server. In a QEMU setup, the client |
| will be a GDB (or LLDB) process and the server will be the QEMU process that's |
| also running the embedded program.</p> |
| <p>In this section we'll use the <code>hello</code> example we already compiled.</p> |
| <p>The first debugging step is to launch QEMU in debugging mode:</p> |
| <pre><code class="language-console">qemu-system-arm \ |
| -cpu cortex-m3 \ |
| -machine lm3s6965evb \ |
| -nographic \ |
| -semihosting-config enable=on,target=native \ |
| -gdb tcp::3333 \ |
| -S \ |
| -kernel target/thumbv7m-none-eabi/debug/examples/hello |
| </code></pre> |
| <p>This command won't print anything to the console and will block the terminal. We |
| have passed two extra flags this time:</p> |
| <ul> |
| <li> |
| <p><code>-gdb tcp::3333</code>. This tells QEMU to wait for a GDB connection on TCP |
| port 3333.</p> |
| </li> |
| <li> |
| <p><code>-S</code>. This tells QEMU to freeze the machine at startup. Without this the |
| program would have reached the end of main before we had a chance to launch |
| the debugger!</p> |
| </li> |
| </ul> |
| <p>Next we launch GDB in another terminal and tell it to load the debug symbols of |
| the example:</p> |
| <pre><code class="language-console">gdb-multiarch -q target/thumbv7m-none-eabi/debug/examples/hello |
| </code></pre> |
| <p><strong>NOTE</strong>: you might need another version of gdb instead of <code>gdb-multiarch</code> depending |
| on which one you installed in the installation chapter. This could also be |
| <code>arm-none-eabi-gdb</code> or just <code>gdb</code>.</p> |
| <p>Then within the GDB shell we connect to QEMU, which is waiting for a connection |
| on TCP port 3333.</p> |
| <pre><code class="language-console">target remote :3333 |
| </code></pre> |
| <pre><code class="language-text">Remote debugging using :3333 |
| Reset () at $REGISTRY/cortex-m-rt-0.6.1/src/lib.rs:473 |
| 473 pub unsafe extern "C" fn Reset() -> ! { |
| </code></pre> |
| <p>You'll see that the process is halted and that the program counter is pointing |
| to a function named <code>Reset</code>. That is the reset handler: what Cortex-M cores |
| execute upon booting.</p> |
| <blockquote> |
| <p>Note that on some setup, instead of displaying the line <code>Reset () at $REGISTRY/cortex-m-rt-0.6.1/src/lib.rs:473</code> as shown above, gdb may print some warnings like :</p> |
| <p><code>core::num::bignum::Big32x40::mul_small () at src/libcore/num/bignum.rs:254</code> |
| <code> src/libcore/num/bignum.rs: No such file or directory.</code></p> |
| <p>That's a known glitch. You can safely ignore those warnings, you're most likely at Reset().</p> |
| </blockquote> |
| <p>This reset handler will eventually call our main function. Let's skip all the |
| way there using a breakpoint and the <code>continue</code> command. To set the breakpoint, let's first take a look where we would like to break in our code, with the <code>list</code> command.</p> |
| <pre><code class="language-console">list main |
| </code></pre> |
| <p>This will show the source code, from the file examples/hello.rs.</p> |
| <pre><code class="language-text">6 use panic_halt as _; |
| 7 |
| 8 use cortex_m_rt::entry; |
| 9 use cortex_m_semihosting::{debug, hprintln}; |
| 10 |
| 11 #[entry] |
| 12 fn main() -> ! { |
| 13 hprintln!("Hello, world!").unwrap(); |
| 14 |
| 15 // exit QEMU |
| </code></pre> |
| <p>We would like to add a breakpoint just before the "Hello, world!", which is on line 13. We do that with the <code>break</code> command:</p> |
| <pre><code class="language-console">break 13 |
| </code></pre> |
| <p>We can now instruct gdb to run up to our main function, with the <code>continue</code> command:</p> |
| <pre><code class="language-console">continue |
| </code></pre> |
| <pre><code class="language-text">Continuing. |
| |
| Breakpoint 1, hello::__cortex_m_rt_main () at examples\hello.rs:13 |
| 13 hprintln!("Hello, world!").unwrap(); |
| </code></pre> |
| <p>We are now close to the code that prints "Hello, world!". Let's move forward |
| using the <code>next</code> command.</p> |
| <pre><code class="language-console">next |
| </code></pre> |
| <pre><code class="language-text">16 debug::exit(debug::EXIT_SUCCESS); |
| </code></pre> |
| <p>At this point you should see "Hello, world!" printed on the terminal that's |
| running <code>qemu-system-arm</code>.</p> |
| <pre><code class="language-text">$ qemu-system-arm (..) |
| Hello, world! |
| </code></pre> |
| <p>Calling <code>next</code> again will terminate the QEMU process.</p> |
| <pre><code class="language-console">next |
| </code></pre> |
| <pre><code class="language-text">[Inferior 1 (Remote target) exited normally] |
| </code></pre> |
| <p>You can now exit the GDB session.</p> |
| <pre><code class="language-console">quit |
| </code></pre> |
| |
| </main> |
| |
| <nav class="nav-wrapper" aria-label="Page navigation"> |
| <!-- Mobile navigation buttons --> |
| <a rel="prev" href="../start/index.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/hardware.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/index.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/hardware.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> |
