1 ##########################
2 Frequently Asked Questions
3 ##########################
10 This document answers some frequently asked questions about Native
11 Client (NaCl) and Portable Native Client (PNaCl, pronounced
12 "pinnacle"). For a high-level overview of Native Client, see the
13 :doc:`Technical Overview <overview>`.
15 If you have questions that aren't covered in this FAQ:
17 * Scan through the :doc:`Release Notes <sdk/release-notes>`.
18 * Search through or ask on the :doc:`Native Client Forums <help>`.
21 What is Native Client Good For?
22 ===============================
24 Why did Google build Native Client?
25 -----------------------------------
27 * **Performance:** Native Client modules run nearly as fast as native
29 * **Security:** Native Client lets users run native compiled code in the
30 browser with the same level of security and privacy as traditional web
34 * Developers can leverage existing code, written in C/C++ or other
35 languages, in their applications without forcing users to install a
37 * This code can interact with the embedding web page as part of an
38 HTML and JavaScript web application, or it can be a self-contained
39 and immersive experience.
41 * **Portability:** Native Client and Portable Native Client applications
44 * The Windows, Mac, Linux or ChromeOS operating systems.
45 * Processors with the x86-32, x86-64, or ARM instruction set
46 architectures. Native Client also has experimental support for MIPS.
48 Portable Native client further enhances the above:
50 * **Performance:** Each PNaCl release brings with it more performance
51 enhancements. Already-released applications get faster over time,
52 conserving user's battery.
53 * **Security:** Users are kept secure with an ever-improving sandbox
54 model which adapts to novel attacks, without affecting
55 already-released applications.
56 * **Convenience:** Developers only need to ship a single ``.pexe`` file,
57 not one ``.nexe`` file per supported architecture.
58 * **Portability:** Developers and users don't need to worry about
59 already-released applications not working on new hardware: PNaCl
60 already supports all architectures NaCl does, and as PNaCl evolves it
61 gains support for new processors and fully uses their capabilities.
63 .. TODO Expand on the PNaCl performance section in another document, and
64 .. link to it here. How does one profile PNaCl code? What are common
65 .. causes of slowness? How can code be made faster? What's the best way
66 .. to use Pepper's asynchronous APIs? What do I need to know about
67 .. threads and inter-thread communications? Can I use SIMD or other
68 .. processor-specific instructions? What about the GPU?
70 For more details, refer to the :doc:`history behind and comparison of
71 NaCl and PNaCl <nacl-and-pnacl>`.
73 When should I use Native Client?
74 --------------------------------
76 The following are some typical use cases. For details, see the
77 :doc:`Technical Overview <overview>`.
79 * Porting existing software components for use in a web application.
80 * Porting legacy desktop applications.
81 * Handling browser-side encryption and decryption for an enterprise
83 * Handling multimedia for a web application.
84 * Handling various aspects of web-based games, including physics engines
87 Native Client is a versatile technology; we expect that it will also be
88 used in many other contexts outside of Chrome.
90 When should I use Portable Native Client?
91 -----------------------------------------
93 See :doc:`NaCl and PNaCl <nacl-and-pnacl>`. In short: PNaCl works on the
94 open web whereas NaCl only works on the Chrome Web Store.
96 How fast does code run in Portable Native Client?
97 -------------------------------------------------
99 Fast! The SPEC2k benchmarks (C, C++ and floating-point benchmarks) give
100 the following overhead for optimized PNaCl compared to regular optimized
111 Note that benchmark performance is sometimes bimodal, so different use
112 cases are likely to achieve better or worse performance than the above
113 averages. For example floating-point heavy code usually exhibits much
114 lower overheads whereas very branch-heavy code often performs worse.
116 Note that PNaCl supports performance features that are often used in
117 native code such as :ref:`threading <language_support_threading>` and
118 :ref:`Portable SIMD Vectors <portable_simd_vectors>`.
122 * `Adapting Software Fault Isolation to Contemporary CPU Architectures
123 <https://nativeclient.googlecode.com/svn/data/site/NaCl_SFI.pdf>`_ (PDF).
124 * `Native Client: A Sandbox for Portable, Untrusted x86 Code
125 <http://research.google.com/pubs/pub34913.html>`_ (PDF).
127 If your code isn't performing as close to native speed as you'd expect,
128 :doc:`let us know <help>`!
130 .. TODO Link to the non-existent performance page! (see above todo).
132 Why use Portable Native Client instead of *<technology X>*?
133 -----------------------------------------------------------
135 Many other technologies can be compared to Portable Native Client:
136 Flash, Java, Silverlight, ActiveX, .NET, asm.js, etc...
138 Different technologies have different strengths and weaknesses. In
139 appropriate contexts, Portable Native Client can be faster, more secure,
140 and/or more compatible across operating systems and architectures than
143 Portable Native Client complement other technologies by giving web
144 developers a new capability: the ability to run fast, secure native code
145 from a web browser in an architecture-independent way.
147 If I want direct access to the OS, should I use Native Client?
148 --------------------------------------------------------------
150 No---Native Client does not provide direct access to the OS or devices,
151 or otherwise bypass the JavaScript security model. For more information,
152 see later sections of this FAQ.
155 Development Environments and Tools
156 ==================================
158 What development environment and development operating system do you recommend?
159 -------------------------------------------------------------------------------
161 You can develop on Windows, Mac, or Linux, and the resulting Native
162 Client or Portable Native Client application will run inside the Google
163 Chrome browser on all those platforms as well as ChromeOS. You can also
164 develop on ChromeOS with Crouton_, and we're working on
165 self-hosting a full development environment on Portable Native Client.
167 Any editor+shell combination should work as well as IDEs like Eclipse,
168 Visual Studio with the :doc:`Native Client Add-In
169 <devguide/devcycle/vs-addin>` on Windows, or Xcode on Mac OSX.
171 I'm not familiar with native development tools, can I still use the Native Client SDK?
172 --------------------------------------------------------------------------------------
174 You may find our :doc:`Tutorial <devguide/tutorial/index>` and :doc:`Building
175 instructions <devguide/devcycle/building>` useful, and you can look at
176 the code and Makefiles for the SDK examples to understand how the
177 examples are built and run.
179 You'll need to learn how to use some tools (like GCC, LLVM, make,
180 Eclipse, Visual Studio, or Xcode) before you can get very far with the
181 SDK. Try seaching for an `introduction to GCC
182 <https://www.google.com/search?q=gcc+introduction>`_.
185 Openness, and Supported Architectures and Languages
186 ===================================================
188 Is Native Client open? Is it a standard?
189 ----------------------------------------
191 Native Client is completely open: the executable format is open and the
192 `source code is open <nacl_project_>`_. Right
193 now the Native Client project is in its early stages, so it's premature
194 to consider Native Client for standardization.
196 We consistenly try to document our design and implementation and hope to
197 standardize Portable Native Client when it gains more traction. A good
198 example is our :doc:`PNaCl bitcode reference manual
199 <reference/pnacl-bitcode-abi>`.
201 What are the supported instruction set architectures?
202 -----------------------------------------------------
204 Portable Native Client uses an architecture-independent format (the
205 ``.pexe``) which can currently be translated to execute on processors
206 with the x86-32, x86-64, and ARM instruction set architectures, as well
207 as experimental support for MIPS. As new architectures come along and
208 become popular we expect Portable Native Client to support them without
209 developers having to recompile their code.
211 Native Client can currently execute on the same architectures as
212 Portable Native Client but is only supported on the Chrome Web
213 Store. Native Client's ``.nexe`` files are architecture-dependent and
214 cannot adapt to new architectures without recompilation, we therefore
215 deem them better suited to a web store than to the open web.
217 With Portable Native Client we deliver a system that has comparable
218 portability to JavaScript and can adapt to new instruction set
219 architectures without requiring recompilation. The web is better when
220 it's platform-independent, and we'd like it to stay that way.
224 Do I have to use C or C++? I'd really like to use another language.
225 -------------------------------------------------------------------
227 Right now only C and C++ are supported directly by the toolchain in the
228 SDK. C# and other languages in the .NET family are supported via the
229 `Mono port <https://github.com/elijahtaylor/mono>`_ for Native
230 Client. Moreover, there are several ongoing projects to support
231 additional language runtimes (e.g. `naclports supports Lua, Python and
233 <https://code.google.com/p/naclports/source/browse#svn%2Ftrunk%2Fsrc%2Fexamples%2Ftools>`_)
234 as well as to compile more languages to LLVM's intermediate
235 representation (e.g. support Haskell with `GHC
236 <http://www.haskell.org/ghc/docs/latest/html/users_guide/code-generators.html>`_
237 or support Fortran with `flang
238 <https://flang-gsoc.blogspot.ie/2013/09/end-of-gsoc-report.html>`_), or
239 transpile languages to C/C++ (source-to-source compilation).
241 If you're interested in getting other languages working, please contact the
242 Native Client team by way of the `native-client-discuss mailing list
243 <https://groups.google.com/group/native-client-discuss>`_.
245 Will you only support Chrome? What about other browsers?
246 --------------------------------------------------------
248 We aim to support multiple browsers. However, a number of features that
249 we consider requirements for a production-quality system that keeps the
250 user safe are difficult to implement without help from the
251 browser. Specific examples are an out-of-process plugin architecture and
252 appropriate interfaces for integrated 3D graphics. We have worked
253 closely with Chromium developers to deliver these features and we are
254 eager to collaborate with developers from other browsers.
256 What's the difference between NPAPI and Pepper?
257 -----------------------------------------------
259 :doc:`Pepper <pepper_stable/index>` (also known as PPAPI) is a new API that
260 lets Native Client modules communicate with the browser. Pepper supports
261 various features that don't have robust support in NPAPI, such as event
262 handling, out-of-process plugins, and asynchronous interfaces. Native
263 Client has transitioned from using NPAPI to using Pepper.
265 Is NPAPI part of the Native Client SDK?
266 ---------------------------------------
268 NPAPI is not supported by the Native Client SDK, and is `deprecated in
270 <http://blog.chromium.org/2013/09/saying-goodbye-to-our-old-friend-npapi.html>`_.
272 Does Native Client support SIMD vector instructions?
273 ----------------------------------------------------
275 Native Client currently supports SSE on x86 and NEON on ARM. Support for
276 AVX on x86 is under way.
278 Portable Native Client supports portable SIMD vectors, as detailed in
279 :ref:`Portable SIMD Vectors <portable_simd_vectors>`.
281 Can I use Native Client for 3D graphics?
282 ----------------------------------------
284 Yes. Native Client supports `OpenGL ES 2.0
285 <https://www.khronos.org/opengles/>`_.
287 To alert the user regarding their hardware platform's 3D feature set
288 before loading a large NaCl application, see :doc:`Vetting the driver in
289 Javascript <devguide/coding/3D-graphics>`.
291 Some GL extensions are exposed to Native Client applications, see the
293 <https://src.chromium.org/viewvc/chrome/trunk/src/ppapi/lib/gl/gles2/gles2.c>`_.
294 This file is part of the GL wrapper supplied by the library
295 ``ppapi_gles2`` which you'll want to include in your project. In most
296 cases extensions map to extensions available on other platforms, or
297 differ very slightly (if they differ, the extension is usually CHROMIUM
298 or ANGLE instead of EXT).
300 .. TODO Improve documentation for GL extensions.
302 Does Native Client support concurrency/parallelism?
303 ---------------------------------------------------
305 Native Client and Portable Native Client both support pthreads,
306 C11/C++11 threads, and low-level synchronization primitives (mutex,
307 barriers, atomic read/modify/write, compare-and-exchange, etc...), thus
308 allowing your Native Client application to utilize several CPU cores.
309 Note that this allows you to modify datastructures concurrently without
310 needing to copy them, which is often a limitation of shared-nothing
311 systems. For more information see :ref:`memory model and atomics
312 <memory_model_and_atomics>` and :ref:`threading
313 <language_support_threading>`.
315 Native Client doesn't support HTML5 Web Workers directly but can
316 interact with JavaScript code which does.
322 Do Native Client modules have access to external devices?
323 ---------------------------------------------------------
325 At this time Native Client modules do not have access to serial ports,
326 camera devices, or microphones: Native Client can only use native
327 resources that today's browsers can access. However, we intend to
328 recommend such features to the standards bodies and piggyback on their
329 efforts to make these resources available inside the browser.
331 You can generally think of Pepper as the C/C++ bindings to the
332 capabilities of HTML5. The goal is for Pepper and JavaScript to evolve
333 together and stay on par with each other with respect to features and
340 What happens to my data when I use Native Client?
341 -------------------------------------------------
343 Users can opt-in to sending usage statistics and crash information in
344 Chrome, which includes usage statistics and crash information about
345 Native Client. Crashes in your code won't otherwise send your
346 information to Google: Google counts the number of such crashes, but
347 does so anonymously without sending your application's data or its debug
350 For additional information about privacy and Chrome, see the `Google
351 Chrome privacy policy
352 <https://www.google.com/chrome/intl/en/privacy.html>`_ and the `Google
353 Chrome Terms of Service
354 <https://www.google.com/chrome/intl/en/eula_text.html>`_.
356 How does Native Client prevent sandboxed code from doing Bad Things?
357 --------------------------------------------------------------------
359 Native Client's sandbox works by validating the untrusted code (the
360 compiled Native Client module) before running it. The validator checks
363 * **Data integrity:** No loads or stores are permitted outside of the
364 data sandbox. In particular this means that once loaded into memory,
365 the binary is not writable. This is enforced by operating system
366 protection mechanisms. While new instructions can be inserted at
367 runtime to support things like JIT compilers, such instructions will
368 be subject to runtime verification according to the following
369 constraints before they are executed.
370 * **No unsafe instructions:** The validator ensures that the Native
371 Client application does not contain any unsafe instructions. Examples
372 of unsafe instructions are ``syscall``, ``int``, and ``lds``.
373 * **Control flow integrity:** The validator ensures that all direct and
374 indirect branches target a safe instruction.
376 The beauty of the Native Client sandbox is in reducing "safe" code to a
377 few simple rules that can be verified by a small trusted validator: the
378 compiler isn't trusted. The same applies to Portable Native Client where
379 even the ``.pexe`` to ``.nexe`` translator, a simplified compiler
380 backend, isn't trusted: it is validated before executing, and so is its
383 In addition to static analysis of untrusted code, the Native Client
384 runtime also includes an outer sandbox that mediates system calls. For
385 more details about both sandboxes, see `Native Client: A Sandbox for
386 Portable, Untrusted x86 Code <http://research.google.com/pubs/pub34913.html>`_
389 How does Google know that the safety measures in Native Client are sufficient?
390 ------------------------------------------------------------------------------
392 Google has taken several steps to ensure that Native Client's security
395 * Open source, peer-reviewed papers describing the design.
396 * A :doc:`security contest <community/security-contest/index>`.
397 * Multiple internal and external security reviews.
398 * The ongoing vigilance of our engineering and developer community.
400 Google is committed to making Native Client safer than JavaScript and
401 other popular browser technologies. If you have suggestions for security
402 improvements, let the team know, by way of the `native-client-discuss
403 mailing list <https://groups.google.com/group/native-client-discuss>`_.
411 Instructions on :ref:`debugging the SDK examples
412 <debugging_the_sdk_examples>` using GDB are available. You can also
413 debug Native Client modules with some :doc:`alternative approaches
414 <devguide/devcycle/debugging>`.
416 How do I build x86-32, x86-64 or ARM ``.nexes``?
417 ------------------------------------------------
419 By default, the applications in the ``/examples`` folder create
420 architecture-independent ``.pexe`` for Portable Native Client. To
421 generate a ``.nexe`` targetting one specific architecture using the
422 Native Client or Portable Native Client toolchains, see the
423 :doc:`Building instructions <devguide/devcycle/building>`.
425 How can my web application determine which ``.nexe`` to load?
426 -------------------------------------------------------------
428 Your application does not need to make the decision of loading an
429 x86-32, x86-64 or ARM ``.nexe`` explicitly---the Native Client runtime
430 examines a manifest file (``.nmf``) to pick the right ``.nexe`` file for
431 a given user. You can generate a manifest file using a Python script
432 that's included in the SDK (see the ``Makefile`` in any of the SDK
433 examples for an illustration of how to do so). Your HTML file specifies
434 the manifest filename in the ``src`` attribute of the ``<embed>``
435 tag. You can see the way the pieces fit together by examining the
436 examples included in the SDK.
438 Is it possible to build a Native Client module with just plain C (not C++)?
439 ---------------------------------------------------------------------------
441 Yes. See the ``"Hello, World!"`` in C example in the SDK under
442 ``examples/tutorial/using_ppapi_simple/``, or the Game of Life example
443 under ``examples/demo/life/life.c``.
445 What UNIX system calls can I make through Native Client?
446 --------------------------------------------------------
448 Native Client doesn't directly expose any system calls from the host OS
449 because of the inherent security risks and because the resulting
450 application would not be portable across operating systems. Instead,
451 Native Client provides portable cross-OS abstractions wrapping or
452 proxying OS functionality or emulating UNIX system calls. For example,
453 Native Client provides an ``mmap()`` system call that behaves much like
454 the standard UNIX ``mmap()`` system call.
456 Is my favorite third-party library available for Native Client?
457 ---------------------------------------------------------------
459 Google has ported several third-party libraries to Native Client; such
460 libraries are available in the naclports_ project. We encourage you to
461 contribute libraries to naclports, and/or to host your own ported
462 libraries, and to `let the team know about it
463 <https://groups.google.com/group/native-client-discuss>`_ when you do.
465 Do all the files in an application need to be served from the same domain?
466 --------------------------------------------------------------------------
468 The ``.nmf``, and ``.nexe`` or ``.pexe`` files must either be served from the
469 same origin as the embedding page or an origin that has been configured
470 correctly using CORS_.
472 For applications installed from the Chrome Web Store the Web Store manifest
473 must include the correct, verified domain of the embedding page.
478 Do I have to do anything special to make my application run on different operating systems?
479 -------------------------------------------------------------------------------------------
481 No. Native Client and Portable Native Client applications run without
482 modification on all supported operating systems.
484 However, to run on different instruction set architectures (such as
485 x86-32, x86-64 or ARM), you currently have to either:
487 * Use Portable Native Client.
488 * Build and supply a separate ``.nexe`` file for each architecture, and
489 make them available on the Chrome Web Store. See :doc:`target
490 architectures <devguide/devcycle/building>` for details about which
491 ``.nexe`` files will run on which architectures.
493 How easy is it to port my existing native code to Native Client?
494 ----------------------------------------------------------------
496 In most cases you won't have to rewrite much, if any, code. The Native
497 Client-specific tools, such as ``pnacl-clang++`` or ``x86_64-nacl-g++``,
498 take care of most of the necessary changes. You may need to make some
499 changes to your operating system calls and interactions with external
500 devices to work with the web. Porting existing Linux libraries is
501 generally straightforward, with large libraries often requiring no
504 The following kinds of code may be more challenging to port:
506 * Code that does direct TCP/IP or UDP networking. For security reasons
507 these APIs are only available to packaged applications, not on the
508 open web, after asking for the appropriate permissions. Native Client
509 is otherwise restricted to the networking APIs available in the
511 * Code that creates processes, including UNIX forks. Creating processes
512 is not supported for security reasons. However, threads are supported.
513 * Code that needs to do local file I/O. Native Client is restricted to
514 accessing URLs and to local storage in the browser (the Pepper file I/O API
515 has access to the same per-application storage that JavaScript has via Local
516 Storage). HTML5 File System can be used, among others. For POSIX compatabiliy
517 the Native Client SDK includes a library called nacl_io which allows the
518 application to interact with all these types of files via standard POSIX I/O
519 functions (e.g. open/fopen/read/write/...). See :doc:`Using NaCl I/O
520 <devguide/coding/nacl_io>` for more details.
522 .. _faq_troubleshooting:
527 My ``.pexe`` isn't loading, help!
528 ---------------------------------
530 * You must use Google Chrome version 31 or greater for Portable Native
531 Client. Make sure you have Portable Native Client installed in
532 ``about:nacl``; if not open ``about:components`` and "Check for
534 * PNaCl ``.pexe`` must be compiled with pepper_31 SDK or higher (earlier
535 SDK versions had experimental support for PNaCl, now deprecated).
536 * Your application can verify that Portable Native Client is supported
537 in JavaScript with ``navigator.mimeTypes['application/x-pnacl'] !==
538 undefined``. This is preferred over checking the Chrome version.
540 My ``.nexe`` files never finish loading. What gives?
541 ----------------------------------------------------
543 Here are ways to resolve some common problems that can prevent loading:
545 * You must use Google Chrome version 14 or greater for Native Client.
546 * If you haven't already done so, enable the Native Client flag in
547 Google Chrome. Type ``about:flags`` in the Chrome address bar, scroll
548 down to "Native Client", click the "Enable" link, scroll down to the
549 bottom of the page, and click the "Relaunch Now" button (all browser
550 windows will restart).
551 * Verify that the Native Client plugin is enabled in Google Chrome. Type
552 ``about:plugins`` in the Chrome address bar, scroll down to "Native
553 Client", and click the "Enable" link. (You do not need to relaunch
554 Chrome after you enable the Native Client plugin).
555 * Make sure that the ``.nexe`` files are being served from a web
556 server. Native Client uses the same-origin security policy, which
557 means that modules will not load in pages opened with the ``file://``
558 protocol. In particular, you can't run the examples in the SDK by
559 simply dragging the HTML files from the desktop into the browser. See
560 :doc:`Running Native Client Applications <devguide/devcycle/running>`
561 for instructions on how to run the httpd.py mini-server included in
563 * The ``.nexe`` files must have been compiled using SDK version 0.5 or
565 * You must load the correct ``.nexe`` file for your machine's specific
566 instruction set architecture (x86-32, x86-64 or ARM). You can ensure
567 you're loading the correct ``.nexe`` file by building a separate
568 ``.nexe`` for each architecture, and using a ``.nmf`` manifest file to
569 let the browser select the correct ``.nexe`` file. Note: the need to
570 select a processor-specific ``.nexe`` goes away with Portable Native
572 * If things still aren't working, :doc:`ask for help <help>`!
574 .. _CORS: http://en.wikipedia.org/wiki/Cross-origin_resource_sharing
575 .. _naclports: https://code.google.com/p/naclports
576 .. _Crouton: https://github.com/dnschneid/crouton