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+<html lang='en-US'>
+<head>
+  <meta charset='utf-8'>
+  <meta name="viewport" content="width=device-width, initial-scale=1">
+  <title>NixOS Notes</title>
+  <meta name="description" content="I had bought a new laptop recently, which was a perfect opportunity to take a
+fresh look at my NixOS setup.">
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+    font-weight: 400; font-style: italic;
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+    <nav>
+      <a class="title" href="/">matklad</a>
+      <a href="/about.html">About</a>
+      <a href="/links.html">Links</a>
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+  <article >
+
+<h1><span>NixOS Notes</span> <time class="meta" datetime="2017-03-25">Mar 25, 2017</time></h1>
+<p><span>I had bought a new laptop recently, which was a perfect opportunity to take a</span>
+<span>fresh look at my </span><a href="http://nixos.org/"><span>NixOS</span></a><span> setup.</span></p>
+<p><span>As usual, there are some hacks and not obvious things which I would like to</span>
+<span>document just in case :)</span></p>
+<section id="If-it-does-not-work-update">
+
+    <h2>
+    <a href="#If-it-does-not-work-update"><span>If it does not work, update</span> </a>
+    </h2>
+<p><span>I</span>&rsquo;<span>ve tried installed a stable 16.09 version first, but live CD didn</span>&rsquo;<span>t manage to</span>
+<span>start the X server properly. This was easy to fix by switching to the then beta</span>
+<span>17.03.</span></p>
+</section>
+<section id="UEFI">
+
+    <h2>
+    <a href="#UEFI"><span>UEFI</span> </a>
+    </h2>
+<p><span>It is my first system which uses </span><a href="https://en.wikipedia.org/wiki/Unified_Extensible_Firmware_Interface"><span>UEFI</span></a><span> instead of BIOS, and I was</span>
+<span>pleasantly surprised by how everything just worked. Documentation contains only</span>
+<span>a short paragraph about UEFI, but it</span>&rsquo;<span>s everything you need. The only hiccup on</span>
+<span>my side happened when I enabled GRUB together with </span><code>systemd-boot</code><span>: you don</span>&rsquo;<span>t</span>
+<span>need GRUB at all, </span><code>system-boot</code><span> is a bootloader which handles everything.</span></p>
+</section>
+<section id="If-it-does-not-work-fix-the-obvious-problem">
+
+    <h2>
+    <a href="#If-it-does-not-work-fix-the-obvious-problem"><span>If it does not work, fix the obvious problem</span> </a>
+    </h2>
+<p><span>After I</span>&rsquo;<span>ve installed everything, I was presented with a blank screen</span>
+<span>instead of my desktop environment (with the live CD everything</span>
+<span>worked). It took me ages to debug the issue, while the fix was super</span>
+<span>trivial: add </span><code>videoDrivers = [ "intel" ];</code><span> to </span><code>xserver</code><span> config and</span>
+<code>"noveau"</code><span> to </span><code>blacklistedKernelModules</code><span>.</span></p>
+</section>
+<section id="Rust">
+
+    <h2>
+    <a href="#Rust"><span>Rust</span> </a>
+    </h2>
+<p><span>While nix is the best way to manage Linux desktop I am aware of,</span>
+<a href="https://github.com/rust-lang-nursery/rustup.rs"><span>rustup</span></a><span> is the most convenient way of managing Rust toolchains.</span>
+<span>Unfortunately it</span>&rsquo;<span>s not easy to make rustup play nicely with NixOS (UPDATE:</span>
+<span>rustup is now packaged in nixpkgs and just works). Rustup downloads binaries of</span>
+<span>the compiler and Cargo, but it is impossible to launch unmodified binaries on</span>
+<span>NixOS because it a lacks conventional loader.</span></p>
+<p><span>The fix I came up with is a horrible hack which goes against</span>
+<span>everything in NixOS. Here it is:</span></p>
+
+<figure class="code-block">
+
+
+<pre><code><span class="line">environment.<span class="hl-attr">extraInit</span> = <span class="hl-keyword">let</span> <span class="hl-attr">loader</span> = <span class="hl-string">&quot;ld-linux-x86-64.so.2&quot;</span>; <span class="hl-keyword">in</span> <span class="hl-string">&#x27;&#x27;</span></span>
+<span class="line"><span class="hl-string">  export LD_LIBRARY_PATH=&quot;$LD_LIBRARY_PATH:/run/current-system/sw/lib:<span class="hl-subst">${pkgs.stdenv.cc.cc.lib}</span>/lib&quot;</span></span>
+<span class="line"><span class="hl-string">  ln -fs <span class="hl-subst">${pkgs.stdenv.cc.libc.out}</span>/lib/<span class="hl-subst">${loader}</span> /lib64/<span class="hl-subst">${loader}</span></span></span>
+<span class="line"><span class="hl-string">&#x27;&#x27;</span>;</span></code></pre>
+
+</figure>
+<p><span>It makes the loader and shared libraries (rustup needs </span><code>zlib</code><span>) visible</span>
+<span>to binaries compiled for x64 Linux.</span></p>
+</section>
+<section id="Idea">
+
+    <h2>
+    <a href="#Idea"><span>Idea</span> </a>
+    </h2>
+<p><span>Another software which I wish to update somewhat more frequently than</span>
+<span>other packages is </span><a href="https://www.jetbrains.com/idea/"><span>IntelliJ IDEA</span></a><span> (I write a fair amount of Kotlin and</span>
+<span>Rust). NixOS has a super convenient mechanism to do this:</span>
+<a href="https://nixos.org/wiki/Nix_Modifying_Packages#Overriding_Existing_Packages"><code>packageOverrides</code></a><span>. Here is my </span><code>~/nixpkgs/config.nix</code><span>:</span></p>
+
+<figure class="code-block">
+
+
+<pre><code><span class="line">{</span>
+<span class="line">  <span class="hl-attr">packageOverrides</span> = pkgs: <span class="hl-keyword">rec</span> {</span>
+<span class="line">    <span class="hl-attr">idea-community</span> = <span class="hl-keyword">let</span></span>
+<span class="line">      <span class="hl-attr">version</span> = <span class="hl-string">&quot;2017.1&quot;</span>;</span>
+<span class="line">      <span class="hl-attr">sha256</span> = <span class="hl-string">&quot;750b517742157475bb690c1cc8f21ac151a754a38fec5c99a4bb473efd71da5d&quot;</span>;</span>
+<span class="line">    <span class="hl-keyword">in</span></span>
+<span class="line">      pkgs.idea.idea-community.overrideDerivation (attrs: <span class="hl-keyword">rec</span> {</span>
+<span class="line">        <span class="hl-keyword">inherit</span> version;</span>
+<span class="line">        <span class="hl-attr">name</span> = <span class="hl-string">&quot;idea-community-<span class="hl-subst">${version}</span>&quot;</span>;</span>
+<span class="line">        <span class="hl-attr">src</span> = pkgs.fetchurl {</span>
+<span class="line">          <span class="hl-keyword">inherit</span> sha256;</span>
+<span class="line">          <span class="hl-attr">url</span> = <span class="hl-string">&quot;https://download.jetbrains.com/idea/ideaIC-<span class="hl-subst">${version}</span>.tar.gz&quot;</span>;</span>
+<span class="line">        };</span>
+<span class="line">      });</span>
+<span class="line">  };</span>
+<span class="line">}</span></code></pre>
+
+</figure>
+<p><span>It allows to use the most recent IDEA with the stable NixOS channel.</span></p>
+</section>
+</article>
+  </main>
+
+  <footer>
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+      <a href="https://github.com/matklad/matklad.github.io/edit/master/content/posts/2017-03-25-nixos-notes.dj">
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+        Fix typo
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diff --git a/2017/10/21/lldb-dynamic-type.html b/2017/10/21/lldb-dynamic-type.html
@@ -0,0 +1,168 @@
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+  <meta name="viewport" content="width=device-width, initial-scale=1">
+  <title>Dynamic types in LLDB</title>
+  <meta name="description" content="If you are wondering how debuggers work, I suggest reading Eli Bendersky's
+eli-on-debuggers. However after having read these notes myself, I still
+had one question unanswered. Namely, how can debugger show fields of a class, if
+the type of the class is known only at runtime?">
+  <link rel="icon" href="/favicon.png" type="image/png">
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+    font-family: 'JetBrains Mono'; src: url('/css/JetBrainsMono-400-Normal.woff2') format('woff2');
+    font-weight: 400; font-style: normal;
+  }
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+    font-family: 'JetBrains Mono'; src: url('/css/JetBrainsMono-700-Normal.woff2') format('woff2');
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+    font-family: 'EB Garamond'; src: url('/css/EBGaramond-400-Normal.woff2') format('woff2');
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+    <nav>
+      <a class="title" href="/">matklad</a>
+      <a href="/about.html">About</a>
+      <a href="/links.html">Links</a>
+      <a href="/blogroll.html">Blogroll</a>
+    </nav>
+  </header>
+
+  <main>
+  <article >
+
+<h1><span>Dynamic types in LLDB</span> <time class="meta" datetime="2017-10-21">Oct 21, 2017</time></h1>
+<p><span>If you are wondering how debuggers work, I suggest reading Eli Bendersky</span>&rsquo;<span>s</span>
+<a href="https://eli.thegreenplace.net/tag/debuggers"><span>eli-on-debuggers</span></a><span>. However after having read these notes myself, I still</span>
+<span>had one question unanswered. Namely, how can debugger show fields of a class, if</span>
+<span>the type of the class is known only at runtime?</span></p>
+<section id="Example">
+
+    <h2>
+    <a href="#Example"><span>Example</span> </a>
+    </h2>
+<p><span>Consider this situation: you have a pointer of type </span><code>A*</code><span>, which at runtime holds</span>
+<span>a value of some subtype of </span><code>A</code><span>. Could the debugger display the fields of the</span>
+<span>actual type? Turns out, it can handle cases like the one below just fine!</span></p>
+
+<figure class="code-block">
+
+
+<pre><code><span class="line"><span class="hl-keyword">struct</span> <span class="hl-title class_">Base</span> { ... };</span>
+<span class="line"></span>
+<span class="line"><span class="hl-keyword">struct</span> <span class="hl-title class_">Derived</span>: Base { ... };</span>
+<span class="line"></span>
+<span class="line"><span class="hl-function"><span class="hl-type">void</span> <span class="hl-title">foo</span><span class="hl-params">(Base&amp; x)</span> </span>{</span>
+<span class="line">    <span class="hl-comment">// `x` can be `Derived` or `Base` here.</span></span>
+<span class="line">    <span class="hl-comment">// How can debugger show fields of `Derived` then?</span></span>
+<span class="line">}</span></code></pre>
+
+</figure>
+</section>
+<section id="DWARF">
+
+    <h2>
+    <a href="#DWARF"><span>DWARF</span> </a>
+    </h2>
+<p><span>Could it be possible that information about dynamic types is present in DWARF?</span>
+<span>If we look at the DWARF, we</span>&rsquo;<span>ll see that there</span>&rsquo;<span>s layout information for both</span>
+<code>Base</code><span> and </span><code>Derive</code><span> types, as well as a entry for </span><code>x</code><span> parameter, which says that</span>
+<span>it has type </span><code>Base</code><span>. And this makes sense: we don</span>&rsquo;<span>t know that </span><code>x</code><span> is  </span><code>Derived</code>
+<span>until runtime! So debugger must somehow figure the type of the variable</span>
+<span>dynamically.</span></p>
+</section>
+<section id="No-Magic">
+
+    <h2>
+    <a href="#No-Magic"><span>No Magic</span> </a>
+    </h2>
+<p><span>As usual, there</span>&rsquo;<span>s no magic. For example, LLDB has a hard-coded knowledge of C++</span>
+<span>programming language, which allows debugger to inspect types at runtime.</span>
+<span>Specifically, this is handled by </span><code>LanguageRuntime</code><span> LLDB </span><strong><span>plugin</span></strong><span>, which has a</span>
+<span>curious function </span><a href="https://github.com/llvm-mirror/lldb/blob/bc19e289f759c26e4840aab450443d4a85071139/include/lldb/Target/LanguageRuntime.h#L82"><code>GetDynamicTypeAndAddress</code></a><span>, whose job is to poke the</span>
+<span>representation of value to get its real type and adjust pointer, if necessary</span>
+<span>(remember, with multiple inheritance, casts may change the value of the</span>
+<span>pointer).</span></p>
+<p><span>The implementation of this function for C++ language lives in</span>
+<a href="https://github.com/llvm-mirror/lldb/blob/bc19e289f759c26e4840aab450443d4a85071139/source/Plugins/LanguageRuntime/CPlusPlus/ItaniumABI/ItaniumABILanguageRuntime.cpp#L185"><span>ItaniumABILanguageRuntime.cpp</span></a><span> although, unlike C, C++ lacks a</span>
+<span>standardized ABI, almost all compilers on all non-windows platforms use a</span>
+<a href="http://refspecs.linuxbase.org/cxxabi-1.83.html"><span>specific ABI</span></a><span>, confusingly called Itanium (after a now effectively dead</span>
+<span>64-bit CPU architecture).</span></p>
+</section>
+</article>
+  </main>
+
+  <footer>
+    <p>
+      <a href="https://github.com/matklad/matklad.github.io/edit/master/content/posts/2017-10-21-lldb-dynamic-type.dj">
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+        Fix typo
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