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diff --git a/toolkit/crashreporter/docs/index.rst b/toolkit/crashreporter/docs/index.rst new file mode 100644 index 000000000..76ab15693 --- /dev/null +++ b/toolkit/crashreporter/docs/index.rst @@ -0,0 +1,195 @@ +============== +Crash Reporter +============== + +Overview +======== + +The **crash reporter** is a subsystem to record and manage application +crash data. + +While the subsystem is known as *crash reporter*, it helps to think of +it more as a *process dump manager*. This is because the heart of this +subsystem is really managing process dump files and these files are +created not only from process crashes but also from hangs and other +exceptional events. + +The crash reporter subsystem is composed of a number of pieces working +together. + +Breakpad + Breakpad is a library and set of tools to make collecting process + information (notably dumps from crashes) easy. Breakpad is a 3rd + party project (originaly developed by Google) that is imported into + the tree. + +Dump files + Breakpad produces files called *dump files* that hold process data + (stacks, heap data, etc). + +Crash Reporter Client + The crash reporter client is a standalone executable that is launched + to handle dump files. This application optionally submits crashes to + Mozilla (or the configured server). + +Minidump Analyzer + The minidump analyzer is a standalone executable that is launched by the + crash reporter client or by the browser itself to extract stack traces from + the dump files generated during a crash. It appends the stack traces to the + .extra file associated with the crash dump. + +How Main-Process Crash Handling Works +===================================== + +The crash handler is hooked up very early in the Gecko process lifetime. +It all starts in ``XREMain::XRE_mainInit()`` from ``nsAppRunner.cpp``. +Assuming crash reporting is enabled, this startup function registers an +exception handler for the process and tells the crash reporter subsystem +about basic metadata such as the application name and version. + +The registration of the crash reporter exception handler doubles as +initialization of the crash reporter itself. This happens in +``CrashReporter::SetExceptionHandler()`` from ``nsExceptionHandler.cpp``. +The crash reporter figures out what application to use for reporting +dumped crashes and where to store these dump files on disk. The Breakpad +exception handler (really just a mechanism for dumping process state) is +initialized as part of this function. The Breakpad exception handler is +a ``google_breakpad::ExceptionHandler`` instance and it's stored as +``gExceptionHandler``. + +As the application runs, various other systems may write *annotations* +or *notes* to the crash reporter to indicate state of the application, +help with possible reasons for a current or future crash, etc. These are +performed via ``CrashReporter::AnnotateCrashReport()`` and +``CrashReporter::AppendAppNotesToCrashReport()`` from +``nsExceptionHandler.h``. + +For well running applications, this is all that happens. However, if a +crash or similar exceptional event occurs (such as a hang), we need to +write a crash report. + +When an event worthy of writing a dump occurs, the Breakpad exception +handler is invoked and Breakpad does its thing. When Breakpad has +finished, it calls back into ``CrashReporter::MinidumpCallback()`` from +``nsExceptionHandler.cpp`` to tell the crash reporter about what was +written. + +``MinidumpCallback()`` performs a number of actions once a dump has been +written. It writes a file with the time of the crash so other systems can +easily determine the time of the last crash. It supplements the dump +file with an *extra* file containing Mozilla-specific metadata. This data +includes the annotations set via ``CrashReporter::AnnotateCrashReport()`` +as well as time since last crash, whether garbage collection was active at +the time of the crash, memory statistics, etc. + +If the *crash reporter client* is enabled, ``MinidumpCallback()`` invokes +it. It simply tries to create a new *crash reporter client* process (e.g. +*crashreporter.exe*) with the path to the written minidump file as an +argument. + +The *crash reporter client* performs a number of roles. There's a lot going +on, so you may want to look at ``main()`` in ``crashreporter.cpp``. First, +stack traces are extracted from the dump via the *minidump analyzer* tool. +The resulting traces are appended to the .extra file of the crash. Then, the +*crash reporter client* verifies that the dump data is sane. If it isn't +(e.g. required metadata is missing), the dump data is ignored. If dump data +looks sane, the dump data +is moved into the *pending* directory for the configured data directory +(defined via the ``MOZ_CRASHREPORTER_DATA_DIRECTORY`` environment variable +or from the UI). Once this is done, the main crash reporter UI is displayed +via ``UIShowCrashUI()``. The crash reporter UI is platform specific: there +are separate versions for Windows, OS X, and various \*NIX presentation +flavors (such as GTK). The basic gist is a dialog is displayed to the user +and the user has the opportunity to submit this dump data to a remote +server. + +If a dump is submitted via the crash reporter, the raw dump files are +removed from the *pending* directory and a file containing the +crash ID from the remote server for the submitted dump is created in the +*submitted* directory. + +If the user chooses not to submit a dump in the crash reporter UI, the dump +files are deleted. + +And that's pretty much what happens when a crash/dump is written! + +Plugin and Child Process Crashes +================================ + +Crashes in plugin and child processes are also managed by the crash +reporting subsystem. + +Child process crashes are handled by the ``mozilla::dom::CrashReporterParent`` +class defined in ``dom/ipc``. When a child process crashes, the toplevel IPDL +actor should check for it by calling TakeMinidump in its ``ActorDestroy`` +Method: see ``mozilla::plugins::PluginModuleParent::ActorDestroy`` and +``mozilla::plugins::PluginModuleParent::ProcessFirstMinidump``. That method +is responsible for calling +``mozilla::dom::CrashReporterParent::GenerateCrashReportForMinidump`` with +appropriate crash annotations specific to the crash. All child-process +crashes are annotated with a ``ProcessType`` annotation, such as "content" or +"plugin". + +Submission of child process crashes is handled by application code. This +code prompts the user to submit crashes in context-appropriate UI and then +submits the crashes using ``CrashSubmit.jsm``. + +Memory Reports +============== + +When a process detects that it is running low on memory, a memory report is +saved. If the process crashes, the memory report will be included with the crash +report. ``nsThread::SaveMemoryReportNearOOM()`` checks to see if the process is +low on memory every 30 seconds at most and saves a report every 3 minutes at +most. Since a child process cannot actually save to the hard drive, it instead +notifies its parent process, which saves the report for it. If a crash does +occur, the memory report is moved to the *pending* directory with the other dump +data and an annotation is added to indicate the presence of the report. This +happens in ``nsExceptionHandler.cpp``, but occurs in different functions +depending on what process crashed. When the main process crashes, this happens +in ``MinidumpCallback()``. When a child process crashes, it happens in +``OnChildProcessDumpRequested()``, with the annotation being added in +``WriteExtraData()``. + +Flash Process Crashes +===================== + +On Windows Vista+, the Adobe Flash plugin creates two extra processes in its +Firefox plugin to implement OS-level sandboxing. In order to catch crashes in +these processes, Firefox injects a crash report handler into the process using the code at ``InjectCrashReporter.cpp``. When these crashes occur, the +ProcessType=plugin annotation is present, and an additional annotation +FlashProcessDump has the value "Sandbox" or "Broker". + +Plugin Hangs +============ + +Plugin hangs are handled as crash reports. If a plugin doesn't respond to an +IPC message after 60 seconds, the plugin IPC code will take minidumps of all +of the processes involved and then kill the plugin. + +In this case, there will be only one .ini file with the crash report metadata, +but there will be multiple dump files: at least one for the browser process and +one for the plugin process, and perhaps also additional dumps for the Flash +sandbox and broker processes. All of these files are submitted together as a +unit. Before submission, the filenames of the files are linked: + +- **uuid.ini** - *annotations, includes an additional_minidumps field* +- **uuid.dmp** - *plugin process dump file* +- **uuid-<other>.dmp** - *other process dump file as listed in additional_minidumps* + +Browser Hangs +============= + +There is a feature of Firefox that will crash Firefox if it stops processing +messages after a certain period of time. This feature doesn't work well and is +disabled by default. See ``xpcom/threads/HangMonitor.cpp``. Hang crashes +are annotated with ``Hang=1``. + +about:crashes +============= + +If the crash reporter subsystem is enabled, the *about:crashes* +page will be registered with the application. This page provides +information about previous and submitted crashes. + +It is also possible to submit crashes from *about:crashes*. |