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diff --git a/docs/contributing/debugging/debugging_on_windows.rst b/docs/contributing/debugging/debugging_on_windows.rst new file mode 100644 index 0000000000..3213299199 --- /dev/null +++ b/docs/contributing/debugging/debugging_on_windows.rst @@ -0,0 +1,330 @@ +Debugging On Windows +==================== + +This document explains how to debug Gecko based applications such as +Firefox, Thunderbird, and SeaMonkey on Windows using the Visual Studio IDE. + +If VS and your Gecko application hang shortly after you launch the +application under the debugger, see `Problems Loading Debug +Symbols <#problems-loading-debug-symbols>`__. + +Ways to start the debugger +~~~~~~~~~~~~~~~~~~~~~~~~~~ + +First of all, it's necessary to install a Visual Studio extension to be +able to follow child processes as they are created. Firefox, in general, +and even in non-e10s mode, does not start the main process directly, it +starts it via a Launcher Process. This means that Visual Studio will +only attach to the first process it finds, and will not hit any +break-point (and even notifies you that it cannot find their location). +`Microsoft Child Process Debugging Power +Tool <https://marketplace.visualstudio.com/items?itemName=vsdbgplat.MicrosoftChildProcessDebuggingPowerTool>`__ +allows automatically attaching to child processes, such as Web Content +process, GPU process, etc. Enable it by going its configuration menu in +"Debug > Other debugging targets > Child process debugging settings", +and ticking the box. + +If you have followed the steps in :ref:`Building Firefox for +Windows <Building Firefox On Windows>` +and have a local debug build, you can **execute this command from same command line.** + +.. code:: + + ./mach run --debug + +It would open Visual Studio with Firefox's +run options configured. You can **click "Start" button** to run Firefox +then, already attached in the debugger. + +Alternatively, if you have generated the Visual Studio solution, via +``./mach build-backend -b VisualStudio``, opening this solution allows +you to run ``firefox.exe`` directly in the debugger. To make it the +startup project, right click on the project and select ``Set As Startup +Project``. It appears bold when it's the case. Breakpoints are kept +across runs, this can be a good way to debug startup issues. + +**Run the program until you hit an assertion.** You will get a dialog +box asking if you would like to debug. Hit "Cancel". The MSDEV IDE will +launch and load the file where the assertion happened. This will also +create a Visual Studio Mozilla project in the directory of the executable +by default. + +**Attach the debugger to an existing Mozilla process**. In the Visual +Studio, select Debug > Attach to Process. If you want to debug a content +process, you can **hover on the tab** of page you want to debug, which +would show the pid. You can then select the process from dialog opened +from "Attach to Process". You can open ``about:processes`` to see the pid +for all subprocesses, including tabs but also GPU, networking etc. +For more information, see `Attach to Running Processes with the Visual Studio +Debugger <http://msdn.microsoft.com/en-us/library/vstudio/3s68z0b3.aspx>`__. + +**Starting an MSIX installed Firefox with the debugger**. In Visual +Studio, select Debug -> Other Debug Targets -> Debug Installed App Package. +In the dialog, select the installed Firefox package you wish to debug +and click "Start". + +Debugging Release and Nightly Builds +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Refer to the steps to :ref:`use the Mozilla symbol +server <Using The Mozilla Symbol Server>` and :ref:`source +server <Using The Mozilla Source Server>` + +Creating a Visual Studio project for Firefox +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Please refer to :ref:`this <Visual Studio Projects>`. + +Changing/setting the executable to debug +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +To change or set the executable to debug, go to Project > Properties > +Debugging > Command. (As of Visual Studio 2022.) + +It should show the executable you are debugging. If it is empty or +incorrect, manually add the correct path to the executable. + +Command line parameters and environment variables +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +To change or set the command line options, go to Project > Properties > +Debugging > Command Arguments. + +Some common options would be the URL of the file you want the browser to +open as soon as it starts, starting the Profile Manager, or selecting a +profile. You can also redirect the console output to a file (by adding +"``> filename.txt``" for example, without the quotes). + +Customizing the debugger's variable value view +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +You can customize how Visual Studio displays classes in the variable view. +By default VS displays "{...}" and you need to click the small + icon +to expand the members. You can change this behaviour, and make Visual +Studio display whatever data member you want in whatever order, formatted +however you like instead of just "{...}". + +You need to locate a file called "gecko.natvis" under toolkit/library. +The file contains a list of types and how they should be displayed in +the debugger. It is XML and after a little practice you should be well +on your way. + +To understand the file in detail refer to `Create custom views of C++ +objects in the debugger using the Natvis framework +<https://docs.microsoft.com/en-us/visualstudio/debugger/create-custom-views-of-native-objects>`__ + +The file already comes with a number of entries that will make your life +easier, like support for several string types. If you need to add a custom +type, or want to change an existing entry for debugging purposes, you can +easily edit the file. For your convenience it is included in all generated +Visual Studio projects, and if you edit and save it within Visual Studio, it +will pick up the changes immediately. + +Handling multiple processes in Visual Studio +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Turn off "Break all processes when one process breaks" to single step a single +process. + +Turning off "Break all processes when one process breaks" adds "Step Into +Current Process", "Step Over Current Process" and "Step Out Current Process" to +the "Debug" menu. + +To single step a single process with the other processes paused: + +- Turn on "Break all processes when one process breaks" +- Hit a breakpoint which stops all processes +- Turn off "Break all processes when one process breaks" +- Now using "Step Into Current Process" will leave the other processes stopped + and just advance the current one. + +Obtaining ``stdout`` and other ``FILE`` handles +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Running the following command in the Command Window in Visual Studio +returns the value of ``stdout``, which can be used with various +debugging methods (such as ``nsGenericElement::List``) that take a +``FILE*`` param: + +.. code:: + + Debug.EvaluateStatement {,,msvcr80d}(&__iob_func()[1]) + +(Alternatively you can evaluate ``{,,msvcr80d}(&__iob_func()[1])`` in +the Immediate window) + +Similarly, you can open a file on the disk using ``fopen``: + +.. code:: + + >Debug.EvaluateStatement {,,msvcr80d}fopen("c:\\123", "w") + 0x10311dc0 { ..snip.. } + >Debug.EvaluateStatement ((nsGenericElement*)0x03f0e710)->List((FILE*)0x10311dc0, 1) + <void> + >Debug.EvaluateStatement {,,msvcr80d}fclose((FILE*)0x10311dc0) + 0x00000000 + +Note that you may not see the debugging output until you flush or close +the file handle. + +Disabling ASSERTIONS +~~~~~~~~~~~~~~~~~~~~ + +There are basically two ways to disable assertions. One requires setting +an environment variable, while the other affects only the currently +running program instance in memory. + +Environment variable +^^^^^^^^^^^^^^^^^^^^ + +There is an environment variable that can disable breaking for +assertions. This is how you would normally set it: + +.. code:: + + set XPCOM_DEBUG_BREAK=warn + +The environment variable takes also other values besides ``warn``, see +``XPCOM_DEBUG_BREAK`` for more details. + +Note that unlike Unix, the default for Windows is not warn, it's to pop +up a dialog. To set the environment variable for Visual Studio, use +Project > Properties > Debugging > Environment and click the little box. +Then use + +.. code:: + + XPCOM_DEBUG_BREAK=warn + +Changing running code +^^^^^^^^^^^^^^^^^^^^^ + +You normally shouldn't need to do this (just quit the application, set +the environment variable described above, and run it again). And this +can be **dangerous** (like **trashing your hard disc and corrupting your +system**). So unless you feel comfortable with this, don't do it. **You +have been warned!** + +It is possible to change the interrupt code in memory (which causes you +to break into debugger) to be a NOP (no operation). + +You do this by running the program in the debugger until you hit an +assertion. You should see some assembly code. One assembly code +instruction reads "int 3". Check the memory address for that line. Now +open memory view. Type/copy/drag the memory address of "int 3" into the +memory view to get it to update on that part of the memory. Change the +value of the memory to "90", close the memory view and hit "F5" to +continue. + +Automatically handling ASSERTIONS without a debugger attached +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +When an assertion happens and there is not a debugger attached, a small +helper application +(```windbgdlg.exe`` </En/Automatically_Handle_Failed_Asserts_in_Debug_Builds>`__) +is run. That application can automatically select a response to the "Do +you want to debug" dialog instead of prompting if you configure it, for +more info, see +```windbgdlg.exe`` </En/Automatically_Handle_Failed_Asserts_in_Debug_Builds>`__. + +Debugging optimized builds +~~~~~~~~~~~~~~~~~~~~~~~~~~ + +To effectively debug optimized builds, you should enable debugging +information which effectively leaves the debug symbols in optimized code +so you can still set breakpoints etc. Because the code is optimized, +stepping through the code may occasionally provide small surprises when +the debugger jumps over something. + +You need to make sure this configure parameter is set: + +.. code:: + + ac_add_options --enable-debug + +You can also choose to include or exclude specific modules. + +Console debugging +~~~~~~~~~~~~~~~~~ + +When printing to STDOUT from a content process, the console message will +not appear on Windows. One way to view it is simply to disable e10s +(``./mach run --disable-e10s``) but in order to debug with e10s enabled +one can run + +:: + + ./mach run ... 2>&1 | tee + +It may also be necessary to disable the content sandbox +(``MOZ_DISABLE_CONTENT_SANDBOX=1 ./mach run ...``). + +Running two instances of Mozilla simultaneously +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +You can run two instances of Mozilla (e.g. debug and optimized) +simultaneously by setting the environment variable ``MOZ_NO_REMOTE``: + +.. code:: + + set MOZ_NO_REMOTE=1 + +Or, starting with Firefox 2 and other Gecko 1.8.1-based applications, +you can use the ``-no-remote`` command-line switch instead (implemented +in +`bug 325509 <https://bugzilla.mozilla.org/show_bug.cgi?id=325509>`__). + +You can also specify the profile to use with the ``-P profile_name`` +command-line argument. + +Debugging JavaScript +~~~~~~~~~~~~~~~~~~~~ + +You can use helper functions from +`nsXPConnect.cpp <https://searchfox.org/mozilla-central/source/js/xpconnect/src/nsXPConnect.cpp>`__ +to inspect and modify the state of JavaScript code from the MSVS +debugger. + +For example, to print current JavaScript stack to stdout, evaluate this +in Immediate window: + +.. code:: + + {,,xul}DumpJSStack() + +Visual Studio will show you something in the quick watch window, but +not the stack, you have to look in the OS console for the output. + +Also this magical command only works when you have JS on the VS stack. + +Debugging minidumps +~~~~~~~~~~~~~~~~~~~ + +See :ref:`debugging a minidump <Debugging A Minidump>`. + +Problems post-mortem debugging on Windows 7 SP1 x64? +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +If you attempt to use ``NS_DebugBreak`` etc to perform post-mortem +debugging on a 64bit Windows 7, but as soon as you try and continue +debugging the program crashes with an Access Violation, you may be +hitting a Windows bug relating to AVX support. For more details, +including a work-around see `this blog +post <http://www.os2museum.com/wp/?p=960>`__ or `this social.msdn +thread <http://social.msdn.microsoft.com/Forums/vstudio/en-US/392ca62c-e502-42d9-adbc-b4e22d5da0c3/jit-debugging-32bit-app-crashing-with-access-violation>`__. +(And just in-case those links die, the work-around is to execute + +:: + + bcdedit /set xsavedisable 1 + +from an elevated command-prompt to disable AVX support.) + +Got a tip? +~~~~~~~~~~ + +If you think you know a cool Mozilla debugging trick, feel free to +discuss it with `#developers <https://chat.mozilla.org/#/room/#developers:mozilla.org>`__ and +then post it here. + +.. |Screenshot of disabling assertions| image:: https://developer.mozilla.org/@api/deki/files/420/=Win32-debug-nop.png + :class: internal |