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diff --git a/docs/contributing/debugging/debugging_on_macos.rst b/docs/contributing/debugging/debugging_on_macos.rst new file mode 100644 index 0000000000..ef42c162f9 --- /dev/null +++ b/docs/contributing/debugging/debugging_on_macos.rst @@ -0,0 +1,359 @@ +Debugging On macOS +================== + +This document explains how to debug Gecko-based applications such as +Firefox, Thunderbird, and SeaMonkey on macOS using Xcode. If you want to +debug from the terminal see :ref:`Debugging Mozilla with +lldb <Debugging Firefox with LLDB>`. For specific +information on a way to debug hangs, see :ref:`Debugging a hang on macOS <Debugging A Hang On macOS>`. + +Creating a debuggable build +--------------------------- + +First, you need to build the application you're going to debug using +this in your .mozconfig + +.. code:: + + ac_add_options --disable-optimize + ac_add_options --enable-debug-symbols + +you can also add this flag if you want assertions etc. compiled in + +.. code:: + + ac_add_options --enable-debug + +See :ref:`Building Firefox for macOS <Building Firefox On MacOS>` +if you need help creating your own build. + +Debugging Firefox on macOS 10.14+ +--------------------------------- + +macOS 10.14 introduced Notarization and Hardened Runtime features for +improved application security. macOS 10.15 went further, requiring +applications to be Notarized with Hardened Runtime enabled in order to +launch (ignoring workarounds). When run on earlier macOS versions, +Notarization and Hardened Runtime settings have no effect. + +Official Builds +~~~~~~~~~~~~~~~ + +At this time, official builds of Firefox 69 and later are Notarized. +**As a result, it is not possible to attach a debugger to these official +Firefox releases on macOS 10.14+ without disabling System Integrity +Protection (SIP).** This is due to Notarization requiring Hardened +Runtime to be enabled with the ``com.apple.security.get-task-allow`` +entitlement disallowed. **Rather than disabling SIP (which has security +implications), it is recommended to debug with try builds or local +builds. The differences are explained below.** + +try Server Builds +~~~~~~~~~~~~~~~~~ + +In most cases, developers needing to debug a build as close as possible +to the production environment should use a :ref:`try +build <Pushing to Try>`. These +builds enable Hardened Runtime and only differ from production builds in +that they are not Notarized which should not otherwise affect +functionality, (other than the ability to easily launch the browser on +macOS 10.15+ -- see quarantine note below). At this time, developers can +obtain a Hardened Runtime build with the +``com.apple.security.get-task-allow`` entitlement allowed by submitting +a try build and downloading the dmg generated by the "Rpk" shippable +build job. A debugger can be attached to Firefox processes of these +builds. try builds use the ``developer.entitlements.xml`` file from the +source tree while production builds use ``production.entitlements.xml``. +**On macOS 10.15+, downloaded try builds will not launch by default +because Notarization is required. To workaround this problem, remove the +quarantine extended attribute from the downloaded Nightly:** + + ``$ xattr -r -d com.apple.quarantine /Path/to/Nightly.app`` + +Local Builds +~~~~~~~~~~~~ + +Local builds of mozilla-central do not enable Hardened Runtime and hence +do not have debugging restrictions. As a result, some functionality will +be permitted on local builds, but blocked on production builds which +have Hardened Runtime enabled. `Bug +1522409 <https://bugzilla.mozilla.org/show_bug.cgi?id=1522409>`__ was +filed to automate codesigning local builds to enable Hardened Runtime by +default and eliminate this discrepancy. + +To obtain a Hardened Runtime build without using try infrastructure, a +developer can manually codesign builds using the macOS ``codesign(1)`` +command with the ``developer.entitlements.xml`` file from the tree. This +requires creating a codesigning identity. + +Disabling System Integrity Protection (SIP) +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +If debugging a production build is required, follow Apple's documented +steps for disabling System Integrity Protection (SIP). Note that +disabling SIP bypasses Hardened Runtime restrictions which can mask some +bugs that only occur with Hardened Runtime so it is recommended to test +fixes with SIP enabled. **Disabling SIP has system security implications +that should be understood before taking this step.** + +Creating an Xcode project +------------------------- + +If you try to create a new Xcode project in an existing directory +then Xcode will delete its existing contents (Xcode will warn you +beforehand). To work around that, the steps below have you initialize +the project outside the Mozilla source tree, close the project, copy +the .xcodeproj project "file" into the source tree, and then reopen +the project to finish setting it up. + +Note also that since Xcode 7.3.1 it doesn't seem to be possible to +have the Xcode project live outside the source tree. If you try to do +that then Xcode will simply **copy** the source files under the +project directory rather than link to them which breaks debugging and the +possibility to modify-rebuild-relaunch from inside Xcode. + +These steps were last updated for Xcode 10.3: + +#. Open Xcode, and create a new Project with File > New Project. Select + the "Cross-platform" tab then under the "Other" template group select + the "Empty" project type. the click Next. Name the project and click + Next. Create/select a temporary directory to contain the project and + then click Create. +#. Before going any further, close the project (File > Close Project) + and open Finder. Find the \*.xcodejproj directory in the temporary + directory, move it into your Mozilla source tree, and then + double-click on it to reopen it. +#. In the left-hand pane in Xcode you should see a tree item where the + root item has the project name. If the temporary directory that you + originally created the Xcode project in is under that, right click it + and delete it. Now, right click on the root item, select 'Add files + to "<project-name>"', select all the files and directories in your + source directory, untick "Copy items if needed", then click Add. + (These will then be progressively added under the root item + <project-name> in the left-hand pane. Note that subdirectories may + initially appear to be empty, but they too will progressively be + populated as Xcode processes the sourse files. Once done, you should + be able to open any file quickly by hitting Cmd-Shift-O and typing in + the name of a file.) +#. In the Product menu, select Scheme > New Scheme and name your scheme + (for example, "Debug"). After you click OK, Xcode should open the + settings window for the new scheme. (If not, then open its settings + from the Product > Edit Scheme menu.) +#. Select "Run" on the left-hand side of the settings window, then + select the "Info" tab. Set the Executable by clicking on "None" and + selecting "Other...". A new dialog titled "Choose an executable to + launch" will pop up. Browse to the ``.app`` file that you want to + debug (``Firefox.app``, ``Nightly``\ ``Debug.app`` etc). The ``.app`` + file is typically found inside the ``dist`` folder in your build + directory. +#. If you are debugging Firefox, Thunderbird, or some other application + that supports multiple profiles, using a separate profile for + debugging purposes is recommended. See "Having a profile for + debugging purposes" below. Select the "Arguments" tab in the scheme + editor, and click the '+' below the "Arguments passed on launch" + field. Add "-P *profilename*", where *profilename* is the name of a + profile you created previously. Repeat that to also add the argument + "-no-remote". +#. Also in the "Arguments" panel, you may want to add an environment + variable MOZ_DEBUG_CHILD_PROCESS set to the value 1 to help with + debugging e10s. +#. Select "Build" from the left of the scheme editor window, and check + that there is nothing listed under Targets (otherwise it may cause + problems when you try to run the executable for debugging since you + will get build errors). +#. Click "Close" to close the scheme editor. + +At this point you can run the application from Xcode, and when you pause +or hit breakpoints it should show open the correct source file at the +correct line. + +Setting up lldb +--------------- + +``lldb`` is the debugger Xcode provides/uses. + +.. warning:: + + One important issue that the Mozilla .lldbinit file fixes is that by + default some breakpoints will be listed as "pending", and Xcode will + not stop at them. If you don't include the Mozilla's .lldbinit, you + must at least put + ``settings set target.inline-breakpoint-strategy always`` in your + ``$HOME/.lldbinit`` as recommended on :ref:`Debugging Firefox with + lldb <Debugging Firefox with LLDB>`. + +The +`.lldbinit <http://searchfox.org/mozilla-central/source/.lldbinit>`__ +file in the source tree imports many useful `Mozilla specific lldb +settings, commands and +formatters <https://searchfox.org/mozilla-central/source/python/lldbutils/README.txt>`__ +into ``lldb``, but you may need to take one of the following steps to +make sure this file is used. + +If you are using ``lldb`` on the command line (independently of Xcode) +and you will always run it from either the top source directory, the +object directory or else the dist/bin subdirectory of the object +directory, then adding the following setting to your ``$HOME/.lldbinit`` +is sufficient: + +:: + + settings set target.load-cwd-lldbinit true + +*However*, if you will run lldb from a different directory, or if you +will be running it indirectly by debugging in Xcode (Xcode always runs +lldb from "/"), then this setting will not help you. Instead, add the +following to your ``$HOME/.lldbinit``: + +:: + + # This automatically sources the Mozilla project's .lldbinit as soon as lldb + # starts or attaches to a Mozilla app (that's in an object directory). + # + # This is mainly a workaround for Xcode not providing a way to specify that + # lldb should be run from a given directory. (Xcode always runs lldb from "/", + # regardless of what directory Xcode was started from, and regardless of the + # value of the "Custom working directory" field in the Scheme's Run options. + # Therefore setting `settings set target.load-cwd-lldbinit true` can't help us + # without Xcode providing that functionality.) + # + # The following works by setting a one-shot breakpoint to break on a function + # that we know will both run early (which we want when we start first start the + # app) and run frequently (which we want so that it will trigger ASAP if we + # attach to an already running app). The breakpoint runs some commands to + # figure out the object directory path from the attached target and then + # sources the .lldbinit from there. + # + # NOTE: This scripts actions take a few seconds to complete, so the custom + # formatters, commands etc. that are added may not be immediately available. + # + breakpoint set --name nsThread::ProcessNextEvent --thread-index 1 --auto-continue true --one-shot true + breakpoint command add -s python + # This script that we run does not work if we try to use the global 'lldb' + # object, since it is out of date at the time that the script runs (for + # example, `lldb.target.executable.fullpath` is empty). Therefore we must + # get the following objects from the 'frame' object. + target = frame.GetThread().GetProcess().GetTarget() + debugger = target.GetDebugger() + + # Delete our breakpoint (not actually necessary with `--one-shot true`): + target.BreakpointDelete(bp_loc.GetBreakpoint().GetID()) + + # For completeness, find and delete the dummy breakpoint (the breakpoint + # lldb creates when it can't initially find the method to set the + # breakpoint on): + # BUG WORKAROUND! GetID() on the *dummy* breakpoint appears to be returning + # the breakpoint index instead of its ID. We have to add 1 to correct for + # that! :-( + dummy_bp_list = lldb.SBBreakpointList(target) + debugger.GetDummyTarget().FindBreakpointsByName("nsThread::ProcessNextEvent", dummy_bp_list) + dummy_bp_id = dummy_bp_list.GetBreakpointAtIndex(0).GetID() + 1 + debugger.GetDummyTarget().BreakpointDelete(dummy_bp_id) + + # "source" the Mozilla project .lldbinit: + os.chdir(target.executable.fullpath.split("/dist/")[0]) + debugger.HandleCommand("command source -s true " + os.path.join(os.getcwd(), ".lldbinit")) + DONE + +see :ref:`Debugging Mozilla with +lldb <Debugging Firefox with LLDB>`. for more information. + +Having a profile for debugging purposes +--------------------------------------- + +It is recommended to create a separate profile to debug with, whatever +your task, so that you don't lose precious data like Bookmarks, saved +passwords, etc. So that you're not bothered with the profile manager +every time you start to debug, expand the "Executables" branch of the +"Groups & Files" list and double click on the Executable you added for +Mozilla. Click the plus icon under the "Arguments" list and type "-P +<profile name>" (e.g. "-P MozillaDebug"). Close the window when you're +done. + +Running a debug session +----------------------- + +Make sure breakpoints are active (which implies running under the +debugger) by opening the Product menu and selecting "Debug / Activate +Breakpoints" (also shown by the "Breakpoints" button in the top right +section of the main window). Then click the "Run" button or select "Run" +from the Product menu. + +Setting breakpoints +~~~~~~~~~~~~~~~~~~~ + +Setting a breakpoint is easy. Just open the source file you want to +debug in Xcode, and click in the margin to the left of the line of code +where you want to break. + +During the debugging session, each time that line is executed, the +debugger will break there, and you will be able to debug it. + +.. warning:: + + Note that with the default configuration, some breakpoints will be + listed as "pending", and Xcode will not stop at them. If you don't + include the Mozilla's .lldbinit, you must at least put + ``settings set target.inline-breakpoint-strategy always`` in your + ``$HOME/.lldbinit`` as recommended on :ref:`Debugging Mozilla with + lldb <Debugging Firefox with LLDB>`. + +Using Firefox-specific lldb commands +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +If you included the .lldbinit when `Setting up +lldb <#setting-up-lldb>`__, you can use Mozilla-specific lldb commands +in the console, located in the Debug area of Xcode. For example, type +``js`` to see the JavaScript stack. For more information, see :ref:`Debugging +Mozilla with lldb <Debugging Firefox with LLDB>`. + +Debugging e10s child processes +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Using Xcode to debug child processes created by an e10s-enabled browser +is a little trickier than debugging a single-process browser, but it can +be done. These directions were written using Xcode 6.3.1 + +#. Complete all the steps above under "Creating the Project" +#. From the "Product" menu, ensure the scheme you created is selected + under "Scheme", then choose "Scheme > Edit Scheme" +#. In the resulting popup, click "Duplicate Scheme" +#. Give the resulting scheme a more descriptive name than "Copy of + Scheme" +#. Select "Run" on the left-hand side of the settings window, then + select the "Info" tab. Set the Executable by clicking on the + "Executable" drop-down, and selecting the ``plugin-container.app`` + that is inside the app bundle of the copy of Firefox you want to + debug. +#. On the same tab, under "Launch" select "Wait for executable to be + launched" +#. On the "Arguments" tab, remove all arguments passed on launch. + +Now you're ready to start debugging: + +#. From the "Product" menu, ensure the scheme you created above is + selected under "Scheme" +#. Click the "Run" button. The information area at the top of the window + will show "Waiting for plugin-container to launch" +#. From a command line, run your build of Firefox. When that launches a + child process (for example, when you start to load a webpage), Xcode + will notice and attach to that child process. You can then debug the + child process like you would any other process. +#. When you are done debugging, click the "Stop" button and quit the + instance of Firefox that you were debugging in the normal way. + +For some help on using lldb see :ref:`Debugging Mozilla with +lldb <Debugging Firefox with LLDB>`. + +Other resources +--------------- + +Apple has an extensive list of `debugging tips and +techniques <https://developer.apple.com/library/mac/#technotes/tn2124/_index.html>`__. + +Questions? Problems? +~~~~~~~~~~~~~~~~~~~~ + +Try asking in our Element channels +`#developers <https://chat.mozilla.org/#/room/#developers:mozilla.org>`__ or +`#macdev <https://chat.mozilla.org/#/room/#macdev:mozilla.org>`__. |