Using DBH

Άρθρο
06/19/2024

DBH is a command-line tool that exposes many of the functions in the DbgHelp API (dbghelp.dll). It can display information about the contents of a symbol file, display specific details of the symbols in the file, and search through the file for symbols matching various criteria. For more information, see Debug Help Library.

The functionality provided by DBH is similar to that provided within WinDbg, KD, and CDB by commands such as x (Examine Symbols).

Running DBH in Interactive Mode

You start DBH with a simple command line, on which you specify the target module whose symbols you wish to investigate. A target module can be an EXE program or a PDB symbol file. You can also specify a process ID (PID) to investigate. See DBH Command-Line Options for the full syntax.

When DBH starts, it loads the symbols for the specified module, and then presents you with a prompt at which you can type a variety of commands. See DBH Commands for a list of available commands.

For example, the following sequence starts DBH by specifying the target process with process ID 4672, then executes the enum command at the DBH prompt to display symbols matching a specific pattern, and then executes the q command to quit DBH:

C:\> dbh -p:4672 
            400000 : TimeTest
          77820000 : ntdll
          77740000 : kernel32

pid:4672 mod:TimeTest[400000]: enum TimeTest!ma* 

 index            address     name
     1             42cc56 :   main
     3             415810 :   malloc
     5             415450 :   mainCRTStartup

pid:4672 mod:TimeTest[400000]: q 

goodbye

Running DBH in Batch Mode

If you wish to run only a single DBH command, you can specify it at the end of the command line. This causes DBH to start, load the specified module, run the specified command, and then exit.

For example, the previous example could be replaced with a single command line:

C:\> dbh -p:4672 enum TimeTest!ma* 
           400000 : TimeTest
         77820000 : ntdll
         77740000 : kernel32

index            address     name
    1             42cc56 :   main
    3             415810 :   malloc
    5             415450 :   mainCRTStartup

This method of running DBH is called batch mode, because it can be easily used in batch files. This version of the command line can also be followed by a pipe ( | ) which redirects the DBH output to another program.

Specifying the Target

DBH can select a target in three ways: by the process ID of a running process, by the name of the executable, or by the name of the symbol file. For example, if there is exactly one instance of MyProg.exe currently running, with process ID 1234, then the following commands are almost equivalent:

C:\> dbh -v -p:1234 
C:\> dbh -v c:\mydir\myprog.exe 
C:\> dbh -v c:\mydir\myprog.pdb

One difference between these commands is that when you start DBH by specifying the process ID, DBH uses the actual virtual addresses being used by this process. When you start DBH by specifying the executable name or the symbol file name, DBH assumes that the module's base address is a standard value (for example, 0x01000000). You can then use the base command to specify the actual base address, thus shifting the addresses of all the symbols in the module.

DBH does not attach to the target process in the way that a debugger does. DBH cannot cause a process to begin or end, nor can it alter how that process runs. For DBH to attach to a process by its process ID, the target process has to be running, but once DBH has been started the target process can be terminated and DBH will continue to access its symbols.

Decorated and Undecorated Symbols

By default, DBH uses undecorated symbol names when displaying and searching for symbols. If you turn off the SYMOPT_UNDNAME symbol option, or include the -d option on the DBH command line, decorations will be included.

For information on symbol decorations, see Public and Private Symbols.

Exiting DBH

To exit DBH, use the q command at the DBH prompt.

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