M-x debug

[Stephen J. Turnbull]

RandomDiscourse writes:

 > Just as I have written it in the Subject, this command exists. It acts
 > differently then "M-x gdb", and for the life of me, I can find absolutely no
 > documentation on it.

C-h f doesn't tell you that it's loaded from "debug.el" or something
like that?

You don't say what you're trying to debug.  M-x debug is for debugging
Emacs Lisp.  Probably there's a manual entry for it, too (C-h C-f
debug RET should take you there).  Use M-x find-library RET debug RET
to learn more about its internals.