Using_the_Mozilla_symbol_server.rst

Using the Mozilla symbol server

===============================

The Mozilla project runs a symbol server for trunk Firefox nightly and

release builds on Windows. Symbols are available for at least 30

previous days worth of nightly builds, and Firefox releases from

2.0.0.4. This allows debugging of those builds without forcing all users

to download large debugging files. The server functions like

`Microsoft's symbol server <https://docs.microsoft.com/windows/win32/dxtecharts/debugging-with-symbols>`__

so the documentation there can be useful.

Note that because Mozilla release builds are heavily optimized,

debugging is not always easy. The debugger will not be able to show you

the content of all variables and the execution path can seem strange

because of inlining, tail calls, and other compiler optimizations. The

only workaround is to build an unoptimized local build.

The official symbol server URL for Firefox is ``https://symbols.mozilla.org/``.

You cannot visit this URL directly: you must add it to the symbol path of your

debugging tool. In the examples below, a local cache directory is used to avoid

repeatedly fetching the PDB from the server. Replace

``C:\Users\myname\symbols`` with an appropriate cache directory on your

machine.

Using the symbol server in Microsoft Visual C++

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

|The Tools menu of Visual C++ with the Options item selected| |The

Visual C++ 2017 Symbols pane of the Options dialog with the Mozilla

symbol server configured|

Using the symbol server in Windbg

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The Windbg symbol path is configured with a string value delimited with

asterisk characters. To use only the Mozilla symbol server, add the

following entry to your symbol path (**note:** you can replace ``C:\symcache\``

with any writable directory on your computer, if you'd prefer a different

location for downloaded symbols):

.. code::

    SRV*c:\symcache\*https://symbols.mozilla.org/

Set this string as ``_NT_SYMBOL_PATH`` in the environment, using

the Windbg menus, or by typing the ``.sympath`` command. If you

would like to get symbols from Microsoft's symbol server as well, you

should list that first (**note:** you can replace ``C:\symcache\``

with any writable directory on your computer, if you'd prefer a different

location for downloaded symbols):

.. code::

    SRV*c:\symcache\*http://msdl.microsoft.com/download/symbols;SRV*c:\symcache\*https://symbols.mozilla.org/

|Image:symbol-server-windbg-menu.jpg| |The WinDbg Symbol Search Path

dialog with the Mozilla symbol server configured|

The default symbol server only contains debug information for release builds.

In case you need to debug a minidump which was generated by a try build you'll

need to add the symbol server's `try` URL instead:

.. code::

    SRV*c:\symcache\*https://symbols.mozilla.org/try/

Note that you do not need _both_ URLs; despite its name, the `try`

endpoint-family will return symbols from both release and try builds

(in that order).

Downloading symbols using symchk.exe

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also download the symbols using symchk.exe, part of Microsoft's

Debugging Tools for Windows. The command should look like this (again,

you can replace ``C:\symcache\`` with any writable directory on

your computer, if you'd prefer a different location for downloaded

symbols):

::

    "C:\Program Files (x86)\Windows Kits\10\Debuggers\x64\symchk.exe" /r "C:\Program Files\Mozilla Firefox/*" /s SRV*C:\symcache\*https://symbols.mozilla.org/

Note the ``\*`` after the Mozilla directory. The output of this command should

be similar to:

::

    SYMCHK: api-ms-win-core-file-l1-2-0.dll FAILED  - api-ms-win-core-file-l1-2-0.pdb mismatched or not found

    SYMCHK: api-ms-win-core-file-l2-1-0.dll FAILED  - api-ms-win-core-file-l2-1-0.pdb mismatched or not found

    SYMCHK: api-ms-win-core-localization-l1-2-0.dll FAILED  - api-ms-win-core-localization-l1-2-0.pdb mismatched or not found

    SYMCHK: api-ms-win-core-processthreads-l1-1-1.dll FAILED  - api-ms-win-core-processthreads-l1-1-1.pdb mismatched or not found

    SYMCHK: api-ms-win-core-synch-l1-2-0.dll FAILED  - api-ms-win-core-synch-l1-2-0.pdb mismatched or not found

    SYMCHK: api-ms-win-core-timezone-l1-1-0.dll FAILED  - api-ms-win-core-timezone-l1-1-0.pdb mismatched or not found

    SYMCHK: api-ms-win-crt-conio-l1-1-0.dll FAILED  - api-ms-win-crt-conio-l1-1-0.pdb mismatched or not found

    SYMCHK: api-ms-win-crt-convert-l1-1-0.dll FAILED  - api-ms-win-crt-convert-l1-1-0.pdb mismatched or not found

    SYMCHK: api-ms-win-crt-environment-l1-1-0.dll FAILED  - api-ms-win-crt-environment-l1-1-0.pdb mismatched or not found

    SYMCHK: api-ms-win-crt-filesystem-l1-1-0.dll FAILED  - api-ms-win-crt-filesystem-l1-1-0.pdb mismatched or not found

    SYMCHK: api-ms-win-crt-heap-l1-1-0.dll FAILED  - api-ms-win-crt-heap-l1-1-0.pdb mismatched or not found

    SYMCHK: api-ms-win-crt-locale-l1-1-0.dll FAILED  - api-ms-win-crt-locale-l1-1-0.pdb mismatched or not found

    SYMCHK: api-ms-win-crt-math-l1-1-0.dll FAILED  - api-ms-win-crt-math-l1-1-0.pdb mismatched or not found

    SYMCHK: api-ms-win-crt-multibyte-l1-1-0.dll FAILED  - api-ms-win-crt-multibyte-l1-1-0.pdb mismatched or not found

    SYMCHK: api-ms-win-crt-private-l1-1-0.dll FAILED  - api-ms-win-crt-private-l1-1-0.pdb mismatched or not found

    SYMCHK: api-ms-win-crt-process-l1-1-0.dll FAILED  - api-ms-win-crt-process-l1-1-0.pdb mismatched or not found

    SYMCHK: api-ms-win-crt-runtime-l1-1-0.dll FAILED  - api-ms-win-crt-runtime-l1-1-0.pdb mismatched or not found

    SYMCHK: api-ms-win-crt-stdio-l1-1-0.dll FAILED  - api-ms-win-crt-stdio-l1-1-0.pdb mismatched or not found

    SYMCHK: api-ms-win-crt-string-l1-1-0.dll FAILED  - api-ms-win-crt-string-l1-1-0.pdb mismatched or not found

    SYMCHK: api-ms-win-crt-time-l1-1-0.dll FAILED  - api-ms-win-crt-time-l1-1-0.pdb mismatched or not found

    SYMCHK: api-ms-win-crt-utility-l1-1-0.dll FAILED  - api-ms-win-crt-utility-l1-1-0.pdb mismatched or not found

    SYMCHK: d3dcompiler_47.dll   FAILED  - D3DCompiler_47.pdb mismatched or not found

    SYMCHK: maintenanceservice_installer.exe FAILED  - Built without debugging information.

    SYMCHK: msvcp140.dll         FAILED  - msvcp140.amd64.pdb mismatched or not found

    SYMCHK: ucrtbase.dll         FAILED  - ucrtbase.pdb mismatched or not found

    SYMCHK: vcruntime140.dll     FAILED  - vcruntime140.amd64.pdb mismatched or not found

    SYMCHK: helper.exe           FAILED  - Built without debugging information.

    SYMCHK: FAILED files = 27

    SYMCHK: PASSED + IGNORED files = 60

.. _Downloading symbols on Linux / Mac OS X:

Downloading symbols on Linux / Mac OS X

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If you are on Linux and running GDB 7.9 or newer, you can use `this GDB

Python script <https://gist.github.com/luser/193572147c401c8a965c>`__ to

automatically fetch symbols. You will need to source this script before

loading symbols (the part where it spends a few seconds loading each .so

when you attach gdb). If you want to reload symbols, you can try:

::

    nosharedlibrary

    sharedlibrary lib

On older GDB and Mac OS X there is a `Python script to download symbols

from the Mozilla symbol

server <http://hg.mozilla.org/users/jwatt_jwatt.org/fetch-symbols>`__

for :ref:`gdb <Debugging Firefox with GDB>`, Shark and other software

that uses symbols. Note that the symbol file for the XUL library is very

large and takes some time to download. This may make it appear as if the

script has gotten stuck, but it will continue.

Symbol indices are named like so:

symbols.mozilla.org/{lowercased:Name}/{lowercased:Name}-{Version}-{Platform}-{BuildID}-symbols.txt.

The Platform is either 'Darwin' (for Mac) or 'Linux'. The rest of values

are based on the contents of the application.ini file under the [App]

heading: For example, the Thunderbird 3.1b2 release with

Name=Thunderbird, Version=3.1b2, BuildID=20100430125415 would have a

filename of "thunderbird-3.1b2-Linux-20100430125415-symbols.txt" under

the thunderbird directory at symbols.mozilla.org. Its contents are a

list of paths to files, all relative to the directory the

BLAH-symbols.txt file is found in.

The source server

~~~~~~~~~~~~~~~~~

In addition to symbols, Mozilla also has a

:ref:`source server <Using The Mozilla Source Server>`, letting you do

source-level debugging and inspection on demand.

Troubleshooting: Symbols will not download

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

If symbols will not download no matter what you do, the problem may be

that Internet Explorer has been set to the **Work Offline** mode. You

will not receive any warnings of this in Windbg, Visual C++ or Visual

Studio. Even using the command line with symchk.exe to download symbols

will fail. This is because Microsoft uses Internet Explorer's internet &

proxy settings to download the symbol files. Check the File menu of

Internet Explorer to ensure "Work Offline" is unchecked.

.. |The Tools menu of Visual C++ with the Options item selected| image:: img/vs_tools_options.png

   :class: internal

.. |The Visual C++ 2017 Symbols pane of the Options dialog with the Mozilla symbol server configured| image:: img/snip_20170901070042.png

   :class: internal

.. |Image:symbol-server-windbg-menu.jpg| image:: img/symbol-server-windbg-menu.jpg

   :class: internal

.. |The WinDbg Symbol Search Path dialog with the Mozilla symbol server configured| image:: img/snip_20170901081816.png

   :class: internal

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