Add debugging information for nacl_io library.

native_client_sdk/src/doc/devguide/devcycle/debugging.rst

 .. _devcycle-debugging:
 
 #########
 Debugging
 #########
 
 This document describes tools and techniques you can use to debug, monitor,
 and measure your application's performance.
 
 .. contents:: Table Of Contents
@@ skipping 71 matching lines @@
   void logmsg(const char* pMsg){
     fprintf(stdout,"logmsg: %s\n",pMsg);
   }
   void errormsg(const char* pMsg){
     fprintf(stderr,"logerr: %s\n",pMsg);
   }
 
 By default stdout and stderr will appear in Chrome's stdout and stderr stream
 but they can also be redirected as described below.
 
+The stderr from the process is by default visible in the terminal that launched
+chrome (at least on mac and linux). Be sure that when you launch chrome it

[Sam Clegg, 2014/10/01 21:52:15]

The stderr and stderr streams for chrome are available on Mac and Linux by
launching chrome from a terminal window.

(also join this with previous paragraph?)

[jpmedley, 2014/10/07 17:01:43]

Done.

+doesn't attach to an existing instance. One simple way to do this is to pass a
+new directory to chrome as your user data directory (``chrome
+--user-data-dir=<newdir>``). It's also possible to redirect the NaCl's stderr to
+other places such as, for example, :ref:`log files  
+<redirecting-output-to-log>`. 

[Sam Clegg, 2014/10/01 21:52:15]

This last sentence is duplicated from the previous paragraph.  

[jpmedley, 2014/10/07 17:01:43]

Done.

+
+.. _redirecting-output-to-log:
 
 Redirecting output to log files
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 You can redirect stdout and stderr to output files by setting these environment
 variables:
 
 * ``NACL_EXE_STDOUT=c:\nacl_stdout.log``
 * ``NACL_EXE_STDERR=c:\nacl_stderr.log``
 
 There is another variable, ``NACLLOG``, that you can use to redirect Native
 Client's internally-generated messages. This variable is set to stderr by
 default; you can redirect these messages to an output file by setting the
 variable as follows:
 
 * ``NACLLOG=c:\nacl.log``
 
+The exception to this is the :doc:`nacl_io library <../coding/nacl_io>` which
+logs directly to the stderr stream.

[Sam Clegg, 2014/10/01 21:52:14]

I would drop this sentence.  nacl_io is just like all other untrusted libraries
in this sense (since it is untrusted code).  NACLLOG (I think)  only effects
logging from trusted code such as sel_ldr. 

[jpmedley, 2014/10/07 17:01:43]

Done.

+
 .. Note::
   :class: note
 
   **Note:** If you set the ``NACL_EXE_STDOUT``, ``NACL_EXE_STDERR``, or
   ``NACLLOG`` variables to redirect output to a file, you must run Chrome with
   the ``--no-sandbox`` flag.  You must also be careful that each variable points
   to a different file.
 
 Logging calls to Pepper interfaces
 ----------------------------------
@@ skipping 53 matching lines @@
 a ``.pexe`` file extension. The actual extension should not matter, but
 it helps distinguish between the two types of files.
 
 **Note** unlike the finalized copy of the pexe, the non-finalized debug copy
 is not considered stable. This means that a debug copy of the PNaCl
 application created by a Pepper N SDK is only guaranteed to run
 with a matching Chrome version N. If the version of the debug bitcode pexe
 does not match that of Chrome then the translation process may fail, and
 you will see an error message in the JavaScript console.
 
-Also, make sure you are passing the ``-g`` :ref:`compile option
-<compile_flags>` to ``pnacl-clang`` to enable generating debugging info.
-You might also want to omit ``-O2`` from the compile-time and link-time
-options, otherwise GDB not might be able to print variables' values when
-debugging (this is more of a problem with the PNaCl/LLVM toolchain than
-with GCC).
+Also, make sure you are passing the ``-g`` :ref:`compile option <compile_flags>`
+to ``pnacl-clang`` to enable generating debugging info.  You might also want to
+omit ``-O2`` from the compile-time and link-time options, otherwise GDB not
+might be able to print variables' values when debugging (this is more of a
+problem with the PNaCl/LLVM toolchain than with GCC).
 
 Once you have built a non-stable debug copy of the pexe, list the URL of
 that copy in your application's manifest file:
 
 .. naclcode::
 
   {
     "program": {
       "portable": {
         "pnacl-translate": {
           "url": "release_version.pexe",
           "optlevel": 2
         },
         "pnacl-debug": {
           "url": "debug_version.bc",
           "optlevel": 0
         }
       }
     }
   }
 
 Copy the ``debug_version.bc`` and ``nmf`` files to the location that
 your local web server serves files from.
 
 When you run Chrome with ``--enable-nacl-debug``, Chrome will translate
 and run the ``debug_version.bc`` instead of ``release_version.pexe``.
 Once the debug version is loaded, you are ready to :ref:`run nacl-gdb
 <running_nacl_gdb>`
 
-Whether you publish the NMF file containing the debug URL to the release
-web server, is up to you. One reason to avoid publishing the debug URL
-is that it is only guaranteed to work for the Chrome version that matches
-the SDK version. Developers who may have left the ``--enable-nacl-debug``
-flag turned on may end up loading the debug copy of your application
-(which may or may not work, depending on their version of Chrome).
+Whether you publish the NMF file containing the debug URL to the
+release web server, is up to you. One reason to avoid publishing the
+debug URL is that it is only guaranteed to work for the Chrome version
+that matches the SDK version. Developers who may have left the
+``--enable-nacl-debug`` flag turned on may end up loading the debug
+copy of your application (which may or may not work, depending on
+their version of Chrome).
 
 
 Debugging PNaCl pexes (with older Pepper toolchains)
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 If you want to use GDB to debug a program that is compiled with the PNaCl
 toolchain, you must convert the ``pexe`` file to a ``nexe``.  (You can skip
 this step if you are using the GCC toolchain, or if you are using
 pepper 35 or later.)
 
 * Firstly, make sure you are passing the ``-g`` :ref:`compile option
   <compile_flags>` to ``pnacl-clang`` to enable generating debugging info.
   You might also want to omit ``-O2`` from the compile-time and link-time
   options.
 
 * Secondly, use ``pnacl-translate`` to convert your ``pexe`` to one or more
+
   ``nexe`` files.  For example:
 
   .. naclcode::
     :prettyprint: 0
 
     nacl_sdk/pepper_<version>/toolchain/win_pnacl/bin/pnacl-translate \
       --allow-llvm-bitcode-input hello_world.pexe -arch x86-32 \
       -o hello_world_x86_32.nexe
     nacl_sdk/pepper_<version>/toolchain/win_pnacl/bin/pnacl-translate \
       --allow-llvm-bitcode-input hello_world.pexe -arch x86-64 \
@@ skipping 269 matching lines @@
 
 If you cannot use the :ref:`Visual Studio add-in <visual_studio>`, or you want
 to use a debugger other than nacl-gdb, you must manually build your module as a
 Pepper plugin (sometimes referred to as a "`trusted
 <http://www.chromium.org/nativeclient/getting-started/getting-started-background-and-basics#TOC-Trusted-vs-Untrusted>`_"
 or "in-process" plugin).  Pepper plugins (.DLL files on Windows; .so files on
 Linux; .bundle files on Mac) are loaded directly in either the Chrome renderer
 process or a separate plugin process, rather than in Native Client. Building a
 module as a trusted Pepper plugin allows you to use standard debuggers and
 development tools on your system, but when you're finished developing the
-plugin, you need to port it to Native Client (i.e., build the module with one
-of the toolchains in the NaCl SDK so that the module runs in Native Client).
-For details on this advanced development technique, see `Debugging a Trusted
-Plugin
+plugin, you need to port it to Native Client (i.e., build the module with one of
+the toolchains in the NaCl SDK so that the module runs in Native Client).  For
+details on this advanced development technique, see `Debugging a Trusted Plugin
 <http://www.chromium.org/nativeclient/how-tos/debugging-documentation/debugging-a-trusted-plugin>`_.
 Note that starting with the ``pepper_22`` bundle, the NaCl SDK for Windows
 includes pre-built libraries and library source code, making it much easier to
 build a module into a .DLL.
 
-
 .. |menu-icon| image:: /images/menu-icon.png
 .. |puzzle| image:: /images/puzzle.png