1{{+bindTo:partials.standard_nacl_article}} 2 3<section id="nacl-and-pnacl"> 4<span id="id1"></span><h1 id="nacl-and-pnacl"><span id="id1"></span>NaCl and PNaCl</h1> 5<p>This document describes the differences between <strong>Native Client</strong> and 6<strong>Portable Native Client</strong>, and provides recommendations for when to use each.</p> 7<div class="contents local" id="contents" style="display: none"> 8<ul class="small-gap"> 9<li><a class="reference internal" href="#native-client-nacl" id="id3">Native Client (NaCl)</a></li> 10<li><a class="reference internal" href="#portable-native-client-pnacl" id="id4">Portable Native Client (PNaCl)</a></li> 11<li><a class="reference internal" href="#when-to-use-pnacl" id="id5">When to use PNaCl</a></li> 12<li><a class="reference internal" href="#when-to-use-nacl" id="id6">When to use NaCl</a></li> 13</ul> 14 15</div><section id="native-client-nacl"> 16<h2 id="native-client-nacl">Native Client (NaCl)</h2> 17<p>Native Client enables the execution of native code securely inside web 18applications through the use of advanced <a class="reference external" href="/native-client/community/talks#research">Software Fault Isolation (SFI) 19techniques</a>. Since its launch in 202011, Native Client has provided developers with the ability to harness a 21client machine’s computational power to a much fuller extent than traditional 22web technologies, by running compiled C and C++ code at near-native speeds and 23taking advantage of multiple cores with shared memory.</p> 24<p>While Native Client provides operating system independence, it requires 25developers to generate architecture-specific executable modules 26(<strong>nexe</strong> modules) for each hardware platform. This is not only inconvenient 27for developers, but architecture-specific machine code is not portable and thus 28not well-suited for the open web. The traditional method of application 29distribution on the web is through a self-contained bundle of HTML, CSS, 30JavaScript, and other resources (images, etc.) that can be hosted on a server 31and run inside a web browser. With this type of distribution, a website 32created today should still work years later, on all platforms. 33Architecture-specific executables are clearly not a good fit for distribution 34on the web. As a consequence, Native Client has been restricted to 35applications and browser extensions that are installed through the 36Chrome Web Store.</p> 37</section><section id="portable-native-client-pnacl"> 38<h2 id="portable-native-client-pnacl">Portable Native Client (PNaCl)</h2> 39<p>PNaCl solves the portability problem by splitting the compilation process 40into two parts:</p> 41<ol class="arabic simple"> 42<li>compiling the source code to a portable bitcode format, and</li> 43<li>translating the bitcode to a host-specific executable.</li> 44</ol> 45<p>PNaCl enables developers 46to distribute <strong>portable executables</strong> (<strong>pexe</strong> modules) that the hosting 47environment (e.g., the Chrome browser) can translate to native code before 48executing. This portability aligns Native Client with existing open web 49technologies such as JavaScript: A developer can distribute a <strong>pexe</strong> 50as part of an application (along with HTML, CSS, and JavaScript), 51and the user’s machine is simply able to run it.</p> 52<p>With PNaCl, a developer generates a single <strong>pexe</strong> from source code, 53rather than multiple platform-specific nexes. The <strong>pexe</strong> provides both 54architecture- and OS-independence. Since the <strong>pexe</strong> uses an abstract, 55architecture-independent format, it does not suffer from the portability 56problem described above. Future versions of hosting environments should 57have no problem executing the <strong>pexe</strong>, even on new architectures. 58Moreover, if an existing architecture is subsequently enhanced, the 59<strong>pexe</strong> doesn’t even have to be recompiled—in some cases the 60client-side translation will automatically be able to take advantage of 61the new capabilities.</p> 62<p><strong>In short, PNaCl combines the portability of existing web technologies with 63the performance and security benefits of Native Client.</strong></p> 64<p>With the advent of PNaCl, the distribution restriction of Native Client 65can be lifted. Specifically, a <strong>pexe</strong> module can be part of any web 66application—it does not have to be distributed through the Chrome Web 67Store.</p> 68<p>PNaCl is a new technology, and as such it still has a few limitations 69as compared to NaCl. These limitations are described below.</p> 70</section><section id="when-to-use-pnacl"> 71<h2 id="when-to-use-pnacl">When to use PNaCl</h2> 72<p>PNaCl is the preferred toolchain for Native Client, and the only way to deploy 73Native Client modules on the open web. Unless your project is subject to one 74of the narrow limitations described below 75(see <a class="reference internal" href="#when-to-use-nacl"><em>When to use NaCl</em></a>), you should use PNaCl.</p> 76<p>Beginning with version 31, the Chrome browser supports translation of 77<strong>pexe</strong> modules and their use in web applications, without requiring 78any installation (either of a browser plugin or of the applications 79themselves). Native Client and PNaCl are open-source technologies, and 80our hope is that they will be added to other hosting platforms in the 81future.</p> 82<p>If controlled distribution through the Chrome Web Store is an important part 83of your product plan, the benefits of PNaCl are less critical for you. But 84you can still use the PNaCl toolchain and distribute your application 85through the Chrome Web Store, and thereby take advantage of the 86conveniences of PNaCl, such as not having to explicitly compile your application 87for all supported architectures.</p> 88</section><section id="when-to-use-nacl"> 89<span id="id2"></span><h2 id="when-to-use-nacl"><span id="id2"></span>When to use NaCl</h2> 90<p>The limitations below apply to the current release of PNaCl. If any of 91these limitations are critical for your application, you should use 92non-portable NaCl:</p> 93<ul class="small-gap"> 94<li>By its nature, PNaCl does not support architecture-specific 95instructions in an application (i.e., inline assembly), but tries to 96offer high-performance portable equivalents. One such example is 97PNaCl’s <a class="reference internal" href="/native-client/reference/pnacl-c-cpp-language-support.html#portable-simd-vectors"><em>Portable SIMD Vectors</em></a>.</li> 98<li>Currently PNaCl only supports static linking with the <code>newlib</code> 99C standard library (the Native Client SDK provides a PNaCl port of 100<code>newlib</code>). Dynamic linking and <code>glibc</code> are not yet supported. 101Work is under way to enable dynamic linking in future versions of PNaCl.</li> 102<li>In the initial release, PNaCl does not support some GNU extensions 103like taking the address of a label for computed <code>goto</code>, or nested 104functions.</li> 105</ul> 106</section></section> 107 108{{/partials.standard_nacl_article}} 109