A bit of documentation on new debugging features.
This commit is contained in:
Eric Pouech
Alexandre Julliard
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fd0959013f
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I Introduction
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==============
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I.1 Processes and threads: in underlying OS and in Windows
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----------------------------------------------------------
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Before going into the depths of debugging in Wine, here's a small
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overview of process and thread handling in Wine. It has to be clear
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that there are two different beasts: processes/threads from the Unix
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point of view and processes/threads from a Windows point of view.
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Each Windows' thread is implemented as a Unix process (under Linux
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using the clone syscall), meaning that all threads of a same Windows'
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process share the same (unix) address space (currently, one of wine
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limitation is that several windows processes run in the same (unix)
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address space. it's being worked on).
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In the following:
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+ W-process means a process in Windows' terminology
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+ U-process means a process in Unix' terminology
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+ W-thread means a thread in Windows' terminology
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A W-process is made of one or several W-threads.
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Each W-thread is mapped to one and only one U-process. All U-processes
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of a same W-process share the same address space.
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Each Unix process can be identified by two values:
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- the Unix process id (upid in the following)
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- the Windows's thread id (tid)
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Each Windows' process has also a Windows' process (wpid in the
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following). It must be clear that upid and wpid are different and
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shall not be used instead of the other.
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Wpid and tid are defined (Windows) system wide. They must not be
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confused with process or thread handles which, as any handle, is an
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indirection to a system object (in this case process or thread). A
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same process can have several different handles on the same kernel
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object. The handles can be defined as local (the values is only valid
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in a process), or system wide (the same handle can be used by any
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W-process).
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I.2 Wine, debugging and WineDbg
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-------------------------------
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When talking of debugging in Wine, there are at least two levels to
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think of:
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+ the Windows' debugging API.
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+ the Wine integrated debugger, dubbed WineDbg.
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Wine implements most the the Windows' debugging API (the part in
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KERNEL32, not the one in IMAGEHLP.DLL), and allows any program
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(emulated or WineLib) using that API to debug a W-process.
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WineDbg is a WineLib application making use of this API to allow
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debugging both any Wine or WineLib applications as well as Wine itself
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(kernel and all DLLs).
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II WineDbg's modes of invocation
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================================
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II.1 Starting a process
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-----------------------
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Any application (either a Windows' native executable, or a WineLib
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application) can be run through WineDbg. Command line options and
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tricks are the same than for wine:
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winedbg telnet.exe
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winedbg "hl.exe -windowed"
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II.2 Attaching
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--------------
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WineDbg can also launched without any command line argument:
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- if a wineserver is running, WineDbg lists the running W-processes
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(and their wpid:s), and let you pick up the wpid of the W-process you
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want to debug.
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This is (for now) a neat feature for the following reasons:
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* debug an already started application
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+ launching WineDbg this way let WineDbg and the debugged process run
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in a *separate address space* (launching with 'winedbg myprog.exe'
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doesn't), and most of the deadlocks seen when running the debugger
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disappear (because there is no crit sect shared by both
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processes). That's the best (but far from being acceptable) current
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way to debug an application
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This last advantage shall disappear when address space separation is
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in place. At that time, only the ability to debug an already started
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process will remain.
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II.3 On exception
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-----------------
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When something goes wrong, Windows track this as an
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exception. Exceptions exist for segmentation violation, stack
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overflow, division by zero...
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When an exception occurs, Wine checks if the W-process is debugged. If
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so, the exception event is sent to the debugger, which takes care of
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it: end of the story. This mechanism is part of the standard Windows'
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debugging API.
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If the W-process is not debugged, Wine tries to launch a
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debugger. This debugger (normally WineDbg, see III Configuration for
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more details), at startup, attaches to the W-process which generated
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the exception event. In this case, you are able to look at the causes
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of the exception, and either fix the causes (and continue further the
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execution) or dig deeper to understand what went wrong.
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If WineDbg is the standard debugger, the 'pass' and 'cont' commands
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are the two ways to let the process go further for the handling of the
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exception event.
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To be more precise on the way Wine (and Windows) generates exception
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events, when a fault occurs (segmentation violation, stack
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overflow...), the event is first sent to the debugger (this is know as
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a first chance exception). The debugger can give two answers:
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- continue: the debugger had the ability to correct what's generated
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the exception, and is now able to continue process execution.
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- pass: the debugger couldn't correct the cause of the (first chance
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exception). Wine will now try to walk the list of exception handlers
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to see if one of them can handle the exception. If no exception
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handler is found, the exception is sent once again to the debugger to
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indicate the failure of the exception handling.
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Note: since some of Wine's code uses exceptions and try/catch blocks
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to provide some functionality, WineDbg can be entered in such cases
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with segv exceptions. This happens, for example, with IsBadReadPtr
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function. In that case, the pass command shall be used, to let the
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handling of the exception to be done by the catch block in
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IsBadReadPtr.
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II.4 Quitting
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-------------
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Unfortunately, Windows' don't provide a detach kind of API, meaning
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that once you started debugging a process, you must do so until the
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process dies. Killing (or stopping/aborting) the debugger will also
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kill the debugged process.
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This will be true for any Windows' debugging API compliant debugger,
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starting with WineDbg.
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III Configuration
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=================
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III.1 Registry configuration
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----------------------------
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The Windows' debugging API uses a registry entry to know with debugger
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to invoke when an unhandled exception occurs (see II.3 for some
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details).
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Two values in key
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"MACHINE\\Software\\Microsoft\\Windows NT\\CurrentVersion\\AeDebug"
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determine the behavior:
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+ Debugger: this is the command line used to launch the debugger (it
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uses two printf formats (%ld) to pass context dependent information to
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the debugger). You should put here a complete path to your debugger
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(WineDbg can of course be used, but any other Windows' debugging API
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aware debugger will do).
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+ Auto: if this value is zero, a message box will ask the user if
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he/she wishes to launch the debugger when an unhandled exception
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occurs. Otherwise, the debugger is automatically started.
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A regular Wine registry looks like:
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[MACHINE\\Software\\Microsoft\\Windows NT\\CurrentVersion\\AeDebug] 957636538
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"Auto"=dword:00000001
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"Debugger"="/usr/local/bin/winedbg %ld %ld"
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Note 1: creating this key is mandatory. Not doing so will not fire the
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debugger when an exception occurs.
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Note 2: wineinstall sets up this correctly. However, due to some
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limitation of the registry installed, if a previous Wine installation
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exists, it's safer to remove the whole
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[MACHINE\\Software\\Microsoft\\Windows NT\\CurrentVersion\\AeDebug]
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key before running again wineinstall to regenerate this key.
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III.2 WineDbg configuration
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---------------------------
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WineDbg can be configured thru a number of options. Those options are
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stored in the registry, on a per user basis. The key is (in *my*
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registry) [eric\\Software\\Wine\\WineDbg]
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Those options can be read/written while inside WineDbg, as part of the
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debugger expressions. To refer to one of this option, its name must be
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prefixed by a $ sign.
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For example,
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set $BreakAllThreadsStartup = 1
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sets the option 'BreakAllThreadsStartup' to TRUE.
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All the options are read from the registry when WineDbg starts (if no
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corresponding value is found, a default value is used), and are
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written back to the registry when WineDbg exits (hence, all
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modifications to those options are automatically saved when WineDbg
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terminates).
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Here's the list of all options:
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BreakAllThreadsStartup set to TRUE if at all threads start-up the
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debugger stops
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set to FALSE if only at the first thread
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startup of a given process the debugger stops.
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FALSE by default.
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BreakOnCritSectTimeOut set to TRUE if the debugger stops when a
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critical section times out (5 minutes);
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TRUE by default.
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BreakOnAttach, set to TRUE if when WineDbg attaches to an
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existing process after an unhandled exception,
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WineDbg shall be entered on the first attach
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event.
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Since the attach event is meaningless in the
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context of an exception event (the next event
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which is the exception event is of course
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relevant), that option is likely to be FALSE.
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ConChannelMask mask of active debugger output channels on
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console
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StdChannelMask mask of active debugger output channels on
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stderr
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UseXTerm set to TRUE if the debugger uses its own xterm
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window for console input/output
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set to FALSE is the debugger uses the current
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Unix console for input/output
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Those last 3 variables are jointly used in two generic ways:
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1/ default
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ConChannelMask = DBG_CHN_MESG (1)
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StdChannelMask = 0
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UseXTerm = 1
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In this case, all input/output goes into a specific xterm window (but
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all debug messages TRACE/WARN... still goes to tty where wine is run
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from).
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2/ to have all input/output go into the tty where Wine was started
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from (to be used in a X11-free environment)
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ConChannelMask = 0
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StdChannelMask = DBG_CHN_MESG (1)
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UseXTerm = 1
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Those variables also allow, for example for debugging purposes, to
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use:
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ConChannelMask = 0xfff
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StdChannelMask = 0xfff
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UseXTerm = 1
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This allows to redirect all WineDbg output to both tty Wine was
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started from, and xterm debugging window. If Wine (or WineDbg) was
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started with a redirection of stdout and/or stderr to a file (with for
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example >& shell redirect command), you'll get in that file both
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outputs. It may be interesting to look in the relay trace for specific
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values which the process segv:ed on.
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IV WineDbg commands
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===================
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IV.1 Misc
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---------
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abort aborts the debugger
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quit exits the debugger
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help prints some help on the commands
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help info prints some help on info commands
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mode 16 switch to 16 bit mode
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mode 32 switch to 32 bit mode
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IV.2 Flow control
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-----------------
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cont continue execution until next breakpoint or exception.
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pass pass the exception event up to the filter chain.
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step continue execution until next C line of code (enters
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function call)
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next continue execution until next C line of code (doesn't
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enter function call)
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stepi execute next assembly instruction (enters function
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call)
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nexti execute next assembly instruction (doesn't enter
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function call)
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finish do nexti commands until current function is exited
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cont, step, next, stepi, nexti can be postfixed by a number (N),
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meaning that the command must be executed N times.
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IV.3 Breakpoints, watch points
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------------------------------
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enable N enables (break|watch)point #N
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disable N disables (break|watch)point #N
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delete N deletes (break|watch)point #N
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cond N removes any a existing condition to (break|watch)point N
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cond N <expr> adds condition <expr> to (break|watch)point N. <expr>
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will be evaluated each time the breakpoint is hit. If
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the result is a zero value, the breakpoint isn't
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triggered
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break * N adds a breakpoint at address N
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break <id> adds a breakpoint at the address of symbol <id>
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break <id> N adds a breakpoint at the address of symbol <id> (N ?)
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break N adds a breakpoint at line N of current source file
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break adds a breakpoint at current $pc address
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watch * N adds a watch command (on write) at address N (on 4 bytes)
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watch <id> adds a watch command (on write) at the address of
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symbol <id>
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info break lists all (break|watch)points (with state)
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IV.4 Stack manipulation
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-----------------------
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bt print calling stack of current thread
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up goes up one frame in current thread's stack
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up N goes up N frames in current thread's stack
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dn goes down one frame in current thread's stack
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dn N goes down N frames in current thread's stack
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frame N set N as the current frame
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info local prints information on local variables for current
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function
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IV.5 Directory & source file manipulation
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-----------------------------------------
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show dir
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dir <pathname>
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dir
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symbolfile <pathname>
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list lists 10 source lines from current position
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list - lists 10 source lines before current position
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list N lists 10 source lines from line N in current file
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list <path>:N lists 10 source lines from line N in file <path>
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list <id> lists 10 source lines of function <id>
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list * N lists 10 source lines from address N
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You can specify the end target (to change the 10 lines value) using
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the ','. For example:
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list 123, 234 lists source lines from line 123 up to line 234 in
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current file
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list foo.c:1,56 lists source lines from line 1 up to 56 in file foo.c
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IV.6 Displaying
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---------------
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a display is an expression that's evaluated and printed after the
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execution of any WineDbg command
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display lists the active displays
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info display (same as above command)
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display <expr> adds a display for expression <expr>
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display /fmt <expr> adds a display for expression <expr>. Printing
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evaluated <expr> is done using the given format (see
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print command for more on formats)
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del display N deletes display #N
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undisplay N (same as del display)
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IV.7 Disassembly
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----------------
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disas disassemble from current position
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disas <expr> disassemble from address <expr>
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disas <expr>,<expr>disassembles code between addresses specified by
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the two <expr>
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IV.8 Information on Wine's internals
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------------------------------------
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info class <id> prints information on Windows's class <id>
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walk class lists all Windows' class registered in Wine
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info share lists all the dynamic libraries loaded the debugged
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program (including .so files, NE and PE DLLs)
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info module N prints information on module of handle N
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walk module lists all modules loaded by debugged program
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info queue N prints information on Wine's queue N
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walk queue lists all queues allocated in Wine
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info regs prints the value of CPU register
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info segment N prints information on segment N
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info segment lists all allocated segments
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info stack prints the values on top of the stack
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info map lists all virtual mappings used by the debugged
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program
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info wnd N prints information of Window of handle N
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walk wnd lists all the window hierarchy starting from the
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desktop window
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walk wnd N lists all the window hierarchy starting from the
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window of handle N
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walk process lists all w-processes in Wine session
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walk thread lists all w-threads in Wine session
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walk modref (no longer avail)
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IV.9 Memory (reading, writing, typing)
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x <expr> examines memory at <expr> address
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x /fmt <expr> examines memory at <expr> address using format /fmt
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print <expr> prints the value of <expr> (possibly using its type)
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print /fmt <expr> prints the value of <expr> (possibly using its
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type)
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set <lval>=<expr> writes the value of <expr> in <lval>
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whatis <expr> prints the C type of expression <expr>
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/fmt is either /<letter> or /<count><letter>
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letter can be
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s => an ASCII string
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u => an Unicode UTF16 string
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i => instructions (disassemble)
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x => 32 bit unsigned hexadecimal integer
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d => 32 bit signed decimal integer
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w => 16 bit unsigned hexadecimal integer
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c => character (only printable 0x20-0x7f are actually
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printed)
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b => 8 bit unsigned hexadecimal integer
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V Other debuggers
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=================
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V.1 Using other Unix debuggers
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------------------------------
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You can also use other debuggers (like gdb), but you must be aware of
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a few items:
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- you need to attach the unix debugger to the correct unix process
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(representing the correct windows thread) (you can "guess" it from a
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'ps fax' for example: When running the emulator, usually the first
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two upids are for the Windows' application running the desktop, the
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first thread of the application is generally the third upid; when
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running a WineLib program, the first thread of the application is
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generally the first upid)
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Note: even if latest gdb implements the notion of threads, it won't
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work with Wine because the thread abstraction used for implementing
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Windows' thread is not 100% mapped onto the linux posix threads
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implementation. It means that you'll have to spawn a different gdb
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session for each Windows' thread you wish to debug.
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V.2 Using other Windows debuggers
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---------------------------------
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You can use any Windows' debugging API compliant debugger with
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Wine. Some reports have been made of success with VisualStudio
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debugger (in remote mode, only the hub runs in Wine).
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GoVest fully runs in Wine, but is plagued with the same address space
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issues as WineDbg as stated in II.2
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V.3 Main differences between winedbg and regular Unix debuggers
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---------------------------------------------------------------
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+----------------------------------+---------------------------------+
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| WineDbg | gdb |
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+----------------------------------+---------------------------------+
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|WineDbg debugs a Windows' process:|gdb debugs a Windows' thread: |
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|+ the various threads will be |+ a separate gdb session is |
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| handled by the same WineDbg | needed for each thread of |
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| session | Windows' process |
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|+ a breakpoint will be triggered |+ a breakpoint will be triggered |
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| for any thread of the w-process | only for the w-thread debugged |
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+----------------------------------+---------------------------------+
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|WineDbg supports debug information|gdb supports debug information |
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|from: |from: |
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|+ stabs (standard Unix format) |+ stabs (standard Unix format) |
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|+ Microsoft's C, CodeView, .DBG | |
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+----------------------------------+---------------------------------+
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VI Limitations
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==============
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16 bit processes are not supported (but calls to 16 bit code in 32 bit
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applications is).
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Lack of address space separation exhibits some deadlocks.
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Last updated: 5/21/2000 by ericP
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