Getting Started with WinDbg (User-Mode)
WinDbg is a kernel-mode and user-mode debugger that is included in Debugging Tools for Windows. Here we provide hands-on exercises that will help you get started using WinDbg as a user-mode debugger.
For information about how to get Debugging Tools for Windows, see Debugging Tools for Windows (WinDbg, KD, CDB, NTSD).
After you have installed the debugging tools, locate the installation directories for 64-bit (x64) and 32-bit (x86) versions of the tools. For example:
- C:\Program Files (x86)\Windows Kits\10\Debuggers\x64
- C:\Program Files (x86)\Windows Kits\10\Debuggers\x86
Launch Notepad and attach WinDbg
Navigate to your installation directory, and open WinDbg.exe.
On the File menu, choose Open Executable. In the Open Executable dialog box, navigate to the folder that contains notepad.exe (typically, C:\Windows\System32). For File name, enter notepad.exe. Select Open.
Near the bottom of the WinDbg window, in the command line, enter this command:
The output is similar to this:
Symbol search path is: srv* Expanded Symbol search path is: cache*;SRVThe symbol search path tells WinDbg where to look for symbol (PDB) files. The debugger needs symbol files to obtain information about code modules (function names, variable names, and the like).
Enter this command, which tells WinDbg to do its initial finding and loading of symbol files:
To see the symbols for the Notepad.exe module, enter this command:
Note If you don't see any output, enter .reload again.
To see symbols in the Notepad.exe module that contain main, use the examine symbols command like this to list modules that match the mask:
x notepad!wWin*The output is similar to this:
00007ff6`6e76b0a0 notepad!wWinMain (wWinMain) 00007ff6`6e783db0 notepad!wWinMainCRTStartup (wWinMainCRTStartup)To put a breakpoint at notepad!wWinMain, enter this command:
To verify that your breakpoint was set, enter this command:
The output is similar to this:
0 e Disable Clear 00007ff6`6e76b0a0 0001 (0001) 0:**** notepad!wWinMainTo start Notepad running, enter this command:
Notepad runs until it comes to the WinMain function, and then breaks in to the debugger.
Breakpoint 0 hit notepad!wWinMain: 00007ff6`6e76b0a0 488bc4 mov rax,rspTo see a list of code modules that are loaded in the Notepad process, enter this command:
The output is similar to this:
0:000> lm start end module name 00007ff6`6e760000 00007ff6`6e798000 notepad (pdb symbols) C:\ProgramData\Dbg\sym\notepad.pdb\BC04D9A431EDE299D4625AD6201C8A4A1\notepad.pdb 00007ff8`066a0000 00007ff8`067ab000 gdi32full (deferred) 00007ff8`067b0000 00007ff8`068b0000 ucrtbase (deferred) 00007ff8`06a10000 00007ff8`06aad000 msvcp_win (deferred) 00007ff8`06ab0000 00007ff8`06ad2000 win32u (deferred) 00007ff8`06b40000 00007ff8`06e08000 KERNELBASE (deferred) 00007ff8`07220000 00007ff8`072dd000 KERNEL32 (deferred) 00007ff8`07420000 00007ff8`07775000 combase (deferred) 00007ff8`07820000 00007ff8`079c0000 USER32 (deferred) 00007ff8`079c0000 00007ff8`079f0000 IMM32 (deferred) 00007ff8`07c00000 00007ff8`07c2a000 GDI32 (deferred) 00007ff8`08480000 00007ff8`085ab000 RPCRT4 (deferred) 00007ff8`085b0000 00007ff8`0864e000 msvcrt (deferred) 00007ff8`08c40000 00007ff8`08cee000 shcore (deferred) 00007ff8`08db0000 00007ff8`08fa5000 ntdll (pdb symbols) C:\ProgramData\Dbg\sym\ntdll.pdb\53F12BFE149A2F50205C8D5D66290B481\ntdll.pdb 00007fff`f8580000 00007fff`f881a000 COMCTL32 (deferred)To see a stack trace, enter this command:
The output is similar to this:
0:000> k 00 000000c8`2647f708 00007ff6`6e783d36 notepad!wWinMain 01 000000c8`2647f710 00007ff8`07237034 notepad!__scrt_common_main_seh+0x106 02 000000c8`2647f750 00007ff8`08e02651 KERNEL32!BaseThreadInitThunk+0x14 03 000000c8`2647f780 00000000`00000000 ntdll!RtlUserThreadStart+0x21To start Notepad running again, enter this command:
To break in to Notepad, choose Break from the File menu.
To set and verify a breakpoint at ZwWriteFile, enter these commands:
Enter g to start Notepad running again. In the Notepad window, enter some text and choose Save from the File menu. The running code breaks in when it comes to ZwCreateFile. Enter k to see the stack trace.
In the WinDbg window, just to the left of the command line, notice the processor and thread numbers. In this example the current processor number is 0, and the current thread number is 11. So we are looking at the stack trace for thread 11 (which happens to be running on processor 0).
To see a list of all threads in the Notepad process, enter this command (the tilde):
The output is similar to this:
0:011> ~ 0 Id: 5500.34d8 Suspend: 1 Teb: 000000c8`262c4000 Unfrozen 1 Id: 5500.3960 Suspend: 1 Teb: 000000c8`262c6000 Unfrozen 2 Id: 5500.5d68 Suspend: 1 Teb: 000000c8`262c8000 Unfrozen 3 Id: 5500.4c90 Suspend: 1 Teb: 000000c8`262ca000 Unfrozen 4 Id: 5500.4ac4 Suspend: 1 Teb: 000000c8`262cc000 Unfrozen 5 Id: 5500.293c Suspend: 1 Teb: 000000c8`262ce000 Unfrozen 6 Id: 5500.53a0 Suspend: 1 Teb: 000000c8`262d0000 Unfrozen 7 Id: 5500.3ca4 Suspend: 1 Teb: 000000c8`262d4000 Unfrozen 8 Id: 5500.808 Suspend: 1 Teb: 000000c8`262da000 Unfrozen 10 Id: 5500.3940 Suspend: 1 Teb: 000000c8`262dc000 Unfrozen . 11 Id: 5500.28b0 Suspend: 1 Teb: 000000c8`262de000 Unfrozen 12 Id: 5500.12bc Suspend: 1 Teb: 000000c8`262e0000 Unfrozen 13 Id: 5500.4c34 Suspend: 1 Teb: 000000c8`262e2000 UnfrozenIn this example, there are 14 threads with indexes 0 through 13.
To look at the stack trace for thread 0, enter these commands:
The output is similar to this:
0:011> ~0s 0:011> ~0s win32u!NtUserGetProp+0x14: 00007ff8`06ab1204 c3 ret 0:000> k # Child-SP RetAddr Call Site 00 000000c8`2647bd08 00007ff8`07829fe1 win32u!NtUserGetProp+0x14 01 000000c8`2647bd10 00007fff`f86099be USER32!GetPropW+0xd1 02 000000c8`2647bd40 00007ff8`07d12f4d COMCTL32!DefSubclassProc+0x4e 03 000000c8`2647bd90 00007fff`f8609aba SHELL32!CAutoComplete::_EditWndProc+0xb1 04 000000c8`2647bde0 00007fff`f86098b7 COMCTL32!CallNextSubclassProc+0x9a 05 000000c8`2647be60 00007ff8`0782e858 COMCTL32!MasterSubclassProc+0xa7 06 000000c8`2647bf00 00007ff8`0782de1b USER32!UserCallWinProcCheckWow+0x2f8 07 000000c8`2647c090 00007ff8`0782d68a USER32!SendMessageWorker+0x70b 08 000000c8`2647c130 00007ff8`07afa4db USER32!SendMessageW+0xdaTo quit debugging and detach from the Notepad process, enter this command:
Launch your own application and attach WinDbg
Suppose you have written and built this small console application.
...
void MyFunction(long p1, long p2, long p3)
{
long x = p1 + p2 + p3;
long y = 0;
y = x / p2;
}
void main ()
{
long a = 2;
long b = 0;
MyFunction(a, b, 5);
}
For this exercise, we will assume that the built application (MyApp.exe) and the symbol file (MyApp.pdb) are in C:\MyApp\x64\Debug. We will also assume that the application source code is in C:\MyApp\MyApp and that the target machine compiled MyApp.exe.
Open WinDbg.
On the File menu, choose Open Executable. In the Open Executable dialog box, navigate to C:\MyApp\x64\Debug. For File name, enter MyApp.exe. Select Open.
Enter these commands:
.sympath+ C:\MyApp\x64\Debug
Now WinDbg knows where to find symbols and source code for your application. In this case, the source code location doesn't need to be set with .srcpath because the symbols have fully qualified paths to the source files.
Enter these commands:
Your application breaks in to the debugger when it comes to its main function.
WinDbg displays your source code and the Command window.
On the Debug menu, choose Step Into (or press F11). Continue stepping until you have stepped into MyFunction. When you step into the line
y = x / p2, your application will crash and break in to the debugger. The output is similar to this:(1450.1424): Integer divide-by-zero - code c0000094 (first chance) First chance exceptions are reported before any exception handling. This exception may be expected and handled. MyApp!MyFunction+0x44: 00007ff6`3be11064 f77c2428 idiv eax,dword ptr [rsp+28h] ss:00000063`2036f808=00000000Enter this command:
WinDbg displays an analysis of the problem (division by 0 in this case).
FAULTING_IP: MyApp!MyFunction+44 [c:\myapp\myapp\myapp.cpp @ 7] 00007ff6`3be11064 f77c2428 idiv eax,dword ptr [rsp+28h] EXCEPTION_RECORD: ffffffffffffffff -- (.exr 0xffffffffffffffff) ExceptionAddress: 00007ff63be11064 (MyApp!MyFunction+0x0000000000000044) ExceptionCode: c0000094 (Integer divide-by-zero) ExceptionFlags: 00000000 NumberParameters: 0 ... STACK_TEXT: 00000063`2036f7e0 00007ff6`3be110b8 : ... : MyApp!MyFunction+0x44 00000063`2036f800 00007ff6`3be1141d : ... : MyApp!main+0x38 00000063`2036f840 00007ff6`3be1154e : ... : MyApp!__tmainCRTStartup+0x19d 00000063`2036f8b0 00007ffc`b1cf16ad : ... : MyApp!mainCRTStartup+0xe 00000063`2036f8e0 00007ffc`b1fc4629 : ... : KERNEL32!BaseThreadInitThunk+0xd 00000063`2036f910 00000000`00000000 : ... : ntdll!RtlUserThreadStart+0x1d STACK_COMMAND: dt ntdll!LdrpLastDllInitializer BaseDllName ;dt ntdll!LdrpFailureData ;.cxr 0x0 ;kb FOLLOWUP_IP: MyApp!MyFunction+44 [c:\myapp\myapp\myapp.cpp @ 7] 00007ff6`3be11064 f77c2428 idiv eax,dword ptr [rsp+28h] FAULTING_SOURCE_LINE: c:\myapp\myapp\myapp.cpp FAULTING_SOURCE_FILE: c:\myapp\myapp\myapp.cpp FAULTING_SOURCE_LINE_NUMBER: 7 FAULTING_SOURCE_CODE: 3: void MyFunction(long p1, long p2, long p3) 4: { 5: long x = p1 + p2 + p3; 6: long y = 0; > 7: y = x / p2; 8: } 9: 10: void main () 11: { 12: long a = 2; ...
Summary of commands
- Contents command on the Help menu
- .sympath (Set Symbol Path)
- .reload (Reload Module)
- x (Examine Symbols)
- g (Go)
- Break command on the Debug menu
- lm (List Loaded Modules)
- k (Display Stack Backtrace)
- bu (Set Breakpoint)
- bl (Breakpoint List)
- ~ (Thread Status)
- ~s (Set Current Thread)
- .sympath+ (Set Symbol Path) append to existing symbol path
- .srcpath (Set Source Path)
- Step Into command on the Debug menu (F11)
- !analyze -v
- qd (Quit and Detach)
See also
Getting Started with WinDbg (Kernel-Mode)
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