Bcdedit Tips and Tricks For Debugging Part 1

Hello everyone, my name is Sean Walker, and I am on the Platforms OEM team in Washington.  This article is for those people who have had a hard time switching from the old boot.ini configuration to the new BCD store (myself included). Doing the simple tasks such as enabling kernel debugging over com1 are easy to do with bcdedit.exe or the msconfig GUI, you just enable them and reboot the computer. However, if you need to do something more advanced such as break into the early boot process during resume from hibernation, things get a more complicated.

 

This article has some samples for enabling and disabling debug settings that you may not be familiar with, and a list of bcdedit debug settings for Windows Vista/Server 2008 and Windows 7/Server 2008 R2.  This information has been helpful to me for quickly and accurately getting to the debug at hand rather than fumbling around with bcdedit.  Much of the following information has been taken from various sources, including the windbg help files, the OEM team blog, the MSDN bcdedit reference, and the WHDC debugger site.

 

NOTE: For the examples below, you will need to run bcdedit.exe from an administrator (UAC-elevated) command prompt.  To output a summary view of the current state of the BCD store, just run "bcdedit.exe" from the command prompt.  To get detailed information about all of the store(s) that Windows knows about, use the following command:

bcdedit /enum all

 

What is a BCD store?

A BCD store is a binary file that contains boot configuration data for Windows, basically it is a small registry file.  Boot applications use the system BCD store, located on the system partition, during the boot process.  You can also create additional BCD stores in separate files but only one store at a time can be designated as the system store.

 

NOTE: The "/store" switch can be used to specify a particular BCD store for bcdedit commands (instead of the default store).  To enumerate all the settings in another BCD store, in this case e:\bcd_store\BCD, use the following command:

bcdedit /store e:\bcd_store\BCD /enum all

This will show you which options are currently set, and what their values are.  When /store switch is omitted, the system store is used.

 
Using bootdebug

To enable debugging for early boot problems, you may need to enable the bootdebug switch.  This is easy to do with bcdedit:

bcdedit /set bootdebug on

 
However, this only sets bootdebug for the current "boot application", which is generally winload.exe, so it does not break into the very early boot process.  There are multiple applications used for booting, hibernating, and resuming (bootmgr.exe, winload.exe and winresume.exe are examples of these).  Each application (called BCD Objects) has its own settings (called BCD Elements) in the BCD store and each can be modified globally and/or individually.

So, to deal with different (or multiple) debug scenarios, you just enable boot debugging based on the boot application you are concerned with.  For early debugging, you can enable bootdebug for bootmgr:

bcdedit /set {bootmgr} bootdebug on

 
To set bootdebug for winload.exe (which will most often be your current, and default, boot object) all three of the following will give you the same result:

bcdedit /set bootdebug on
bcdedit /set {current} bootdebug on
bcdedit /set {default} bootdebug on

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