.context (Set User-Mode Address Context)

The .context command specifies which page directory of a process will be used for the user-mode address context, or displays the current user-mode address context.

.context [PageDirectoryBase]

Parameters

PageDirectoryBase
Specifies the base address for a page directory of a desired process. The user-mode address context will be set to this page directory. If PageDirectoryBase is zero, the user-mode address context will be set to the page directory for the current system state. If PageDirectoryBase is omitted, the current user-mode address context is displayed.

Environment

Additional Information

For more information about the user-mode address context and other context settings, see Changing Contexts.

Remarks

Generally, when you are doing kernel debugging, the only visible user-mode address space is the one associated with the current process.

The .context command instructs the kernel debugger to use the specified page directory as the user-mode address context. After this command is executed, the debugger will have access to this virtual address space. The page tables for this address space will be used to interpret all user-mode memory addresses. This allows you to read and write to this memory.

The .process (Set Process Context) command has a similar effect. However, the .context command sets the user-mode address context to a specific page directory, while the .process command sets the process context to a specific process. On an x86 processor, these two commands have essentially the same effect. See Process Context for more details.

If you are doing live debugging, you should issue a .cache forcedecodeuser command in addition to the .context command. This forces the debugger to look up the physical addresses of the memory space needed. (This can be slow, because it often means a huge amount of data must be transferred across the debug cable.)

If you are doing crash dump debugging, the .cache command is not needed. However, you will not have access to any portions of the virtual address space of the user-mode process that were paged to disk when the crash occurred.

Here is an example. Use the !process extension to find the directory base for the desired process:

kd> !process 0 0
**** NT ACTIVE PROCESS DUMP ****
PROCESS fe5039e0  SessionId: 0  Cid: 0008    Peb: 00000000  ParentCid: 0000
    DirBase: 00030000  ObjectTable: fe529b68  TableSize:  50.
    Image: System

...

PROCESS fe3c0d60  SessionId: 0  Cid: 0208    Peb: 7ffdf000  ParentCid: 00d4
 DirBase: 0011f000  ObjectTable: fe3d0f48  TableSize:  30.
    Image: regsvc.exe

Now use the .context command with this page directory base.

kd> .context 0011f000

This enables you to examine the address space in various ways. For example, here is the output of the !peb extension:

kd> !peb
PEB at 7FFDF000
    InheritedAddressSpace:    No
    ReadImageFileExecOptions: No
    BeingDebugged:            No
    ImageBaseAddress:         01000000
    Ldr.Initialized: Yes
    Ldr.InInitializationOrderModuleList: 71f40 . 77f68
    Ldr.InLoadOrderModuleList: 71ec0 . 77f58
    Ldr.InMemoryOrderModuleList: 71ec8 . 77f60
        01000000 C:\WINNT\system32\regsvc.exe
        77F80000 C:\WINNT\System32\ntdll.dll
        77DB0000 C:\WINNT\system32\ADVAPI32.dll
        77E80000 C:\WINNT\system32\KERNEL32.DLL
        77D40000 C:\WINNT\system32\RPCRT4.DLL
        77BE0000 C:\WINNT\system32\secur32.dll
    SubSystemData:     0
    ProcessHeap:       70000
    ProcessParameters: 20000
        WindowTitle: "'C:\WINNT\system32\regsvc.exe'"
        ImageFile:    'C:\WINNT\system32\regsvc.exe'
        CommandLine:  'C:\WINNT\system32\regsvc.exe'
        DllPath:     'C:\WINNT\system32;.;C:\WINNT\System32;C:\WINNT\system;C:\WINNT;C:\WINNT\system32;C:\WINNT;C:\WINNT\System32\Wbem;C:\PROGRA~1\COMMON~1\AUTODE~1'
        Environment:  0x10000