How to debug a boot loader?

I debugged small programs using gdb.

I have source code of GRUB. Second stage of GRUB is written in C. Can I debug it using gdb ?

Is it possible to debug a boot loader ? If yes, then how ?

What is boot debug?

The /bootdebug boot option enables or disables boot debugging of the current or specified Windows operating system boot entry.

How do I debug Windows startup?

To enable boot debugging, use the BCDEdit /bootdebug command and specify the appropriate boot component. If you wish to perform kernel debugging after Windows starts, use the BCDEdit /debug command as well. You must also select a debugging connection, just as in normal kernel debugging.