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232 lines
8.5 KiB
ReStructuredText
232 lines
8.5 KiB
ReStructuredText
How to get a stacktrace with WinDbg
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===================================
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+--------------------------------------------------------------------+
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| This page is an import from MDN and the contents might be outdated |
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+--------------------------------------------------------------------+
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Introduction
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------------
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Sometimes you need to get a stacktrace (call stack) for a crash or hang
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but `Breakpad <http://kb.mozillazine.org/Breakpad>`__ fails because it's
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a special crash or a hang. This article describes how to get a
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stacktrace in those cases with WinDbg on Windows. (To get a stacktrace
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for Thunderbird or some other product, substitute the product name where
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ever you see Firefox in this instructions.)
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Requirements
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------------
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To get such a stacktrace you need to install the following software:
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Debugging Tools for Windows
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~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Microsoft distributes the Debugging Tools for Windows for free, those
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include WinDbg which you will need here. Download it from `Install
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Debugging Tools for
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Windows <https://docs.microsoft.com/en-us/windows-hardware/drivers/download-the-wdk>`__.
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(*You'll want the 32-bit version*, even if you are using a 64-bit
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version of Windows) Then install it, the standard settings in the
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installation process are fine.
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A Firefox nightly or release
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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You need a Firefox version for which symbols are availables from the
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:ref:`symbol server <Using The Mozilla Symbol Server>` to use
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with WinDbg. You can use any `official nightly
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build <https://ftp.mozilla.org/pub/firefox/nightly/>`__ or released
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version of Firefox from Mozilla. You can find the latest trunk nightly
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builds under
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`http://ftp.mozilla.org/pub/mozilla.o.../latest-trunk/ <https://ftp.mozilla.org/pub/firefox/nightly/latest-mozilla-central/>`__.
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Debugging
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---------
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To begin debugging, ensure that Firefox is not already running and open
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WinDbg from the Start menu. (Start->All Programs->Debugging Tools for
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Windows->WinDbg) Next, open the **"File"** menu and choose **"Open
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Executable..."**. In the file chooser window that appears, open the
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firefox.exe executable in your Firefox program folder (C:\Program
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Files\Mozilla Firefox).
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You should now see a "Command" text window with debug output at the top
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and an input box at the bottom. Before debugging can start, several
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commands must be entered into the one-line input box at the bottom of
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the Command window.
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.. note::
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Tip: All commands must be entered exactly as written, one line at a
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time, into the bottom of the Command box.
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- Copying and pasting each line is the easiest method to avoid
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mistakes
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- Some commands start with a period (.) or a pipe character (|),
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which is required. (The keystroke for a pipe character on US
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keyboards is SHIFT+\)
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- Submit the log file on a bug or via the support site, even if
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nothing seems to happen during the debug process
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Start debugging
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~~~~~~~~~~~~~~~
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Now that Firefox is opened in the debugger, you need to configure your
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WinDbg to download symbols from the Mozilla symbol server. To load the
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symbols, enter the three commands below, pressing enter after each one.
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(More details are available at :ref:`symbol server <Using The Mozilla Symbol Server>`.)
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::
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.sympath SRV*c:\symbols*http://symbols.mozilla.org/firefox;SRV*c:\symbols*http://msdl.microsoft.com/download/symbols
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.symfix+ c:\symbols
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.reload /f
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Now wait for the symbols to download. This may take some time depending
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on your connection speed; the total size of the Mozilla and Microsoft
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symbols download is around 1.4GB. WinDbg will show "Busy" at the bottom
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of the application window until the download is complete.
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Once the download is complete, you need to configure WinDbg to examine
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child processes, ignore a specific event caused by Flash Player, and
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record a log of loaded modules. You will also want to open a log file to
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save data you collect. To do this, enter these four commands, pressing
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enter after each one.
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::
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.logopen /t c:\temp\firefox-debug.log
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.childdbg 1
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.tlist
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sxn gp
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lm
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If you see firefox.exe listed in the output from .tlist more than once,
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then you are already running the application and need to close the
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running instance first before you start debugging, otherwise you won't
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get useful results.
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Now run Firefox by opening the **Debug** menu and clicking **Go**.
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**While Firefox is running, you will not be able to type any commands
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into the debugger.** After it starts, try to reproduce the crash or
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hanging issue that you are seeing.
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.. note::
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If Firefox fails to start, and you see lines of text followed by a
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command prompt in the debugger, a "breakpoint" may have been
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triggered. If you are prompted for a command but don't see an error
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about a crash, go back to the **Debug** menu and press **Go**.
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Once the browser crashes, you will see an error (such as "Access
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violation") in the WinDbg Command window. If Firefox hangs and there is
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no command prompt available in the debugger, open the **Debug** menu and
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choose **Break.** Once the browser has crashed or been stopped, continue
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with the steps below.
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After the crash or hang
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~~~~~~~~~~~~~~~~~~~~~~~
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You need to capture the debug information to include in a bug comment or
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support request. Enter these three commands, one at a time, to get the
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stacktrace, crash/hang analysis and log of loaded modules. (Again, press
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Enter after each command.)
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::
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~* kp
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!analyze -v -f
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lm
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After these steps are completed, find the file
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**c:\temp\firefox-debug-(Today's Date).txt** on your hard drive. To
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provide the information to the development community, submit this file
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with a `support request <https://support.mozilla.com/>`__ or attach it
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to a related bug on `Bugzilla <https://bugzilla.mozilla.org/>`__.
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Producing a minidump
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~~~~~~~~~~~~~~~~~~~~
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Sometimes the stacktrace alone is not enough information for a developer
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to figure out what went wrong. A developer may ask you for a "minidump"
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or a "full memory dump", which are files containing more information
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about the process. :ref:`You can easily produce minidumps from WinDBG and
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provide them to developers <Capturing a minidump>`.
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FAQ
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Q: I am running Windows 7 (32-bit or 64-bit) and I see an exception in
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the WinDbg command window that says 'ntdll32!LdrpDoDebuggerBreak+0x2c'
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or 'ntdll32!LdrpDoDebuggerBreak+0x30'. What do I do now?
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A: If you see 'int 3' after either of those exceptions, you will need to
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execute the following commands in WinDbg.
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::
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bp ntdll!LdrpDoDebuggerBreak+0x30
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bp ntdll!LdrpDoDebuggerBreak+0x2c
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eb ntdll!LdrpDoDebuggerBreak+0x30 0x90
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eb ntdll!LdrpDoDebuggerBreak+0x2c 0x90
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| Make sure you enter them one at a time and press enter after each one.
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If you use the 64-bit version of Windows, you need to replace "ntdll"
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in these commands with "ntdll32".
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| Q: The first four frames of my stack trace look like this:
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::
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0012fe20 7c90e89a ntdll!KiFastSystemCallRet
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0012fe24 7c81cd96 ntdll!ZwTerminateProcess+0xc
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0012ff20 7c81cdee kernel32!_ExitProcess+0x62
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0012ff34 6000179e kernel32!ExitProcess+0x14
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This looks wrong to me?!
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A: You ran the application without the "Debug child processes also"
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check box being checked. You need to detach the debugger and open the
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application again, this time with the check box being checked.
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Q: WinDbg tells me that it is unable to verify checksum for firefox.exe.
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Is this normal?
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A: Yes, this is normal and can be ignored.
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Q: Should I click yes or no when WinDbg asks me to "Save information for
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workspace?"
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A: Click yes and WinDbg will save you from having to enter in the symbol
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location for Firefox.exe in the future. Click no if you'd rather not
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having WinDbg save this information.
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Q: I'm seeing "wow64" on top of each thread, is that ok ?
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A: No, you are running a 64 bit version of Windbg and trying to debug a
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32 bit version of the mozilla software. Redownload and install the 32
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bit version of windbg.
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Troubleshooting: Symbols will not download
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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If symbols will not download no matter what you do, the problem may be
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that Internet Explorer has been set to the **Work Offline** mode. You
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will not receive any warnings of this in Windbg, Visual C++ or Visual
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Studio. Even using the command line with symchk.exe to download symbols
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will fail. This is because Microsoft uses Internet Explorer's internet &
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proxy settings to download the symbol files. Check the File menu of
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Internet Explorer to ensure "Work Offline" is unchecked.
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See also
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--------
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- :ref:`symbol server <Using The Mozilla Symbol Server>` Maps addresses to human readable strings.
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- :ref:`source server <Using The Mozilla Source Server>` Maps addresses to source code lines
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