The manual is worth a read. This is a software (as gcc) in which the "man" page or the information displayed with "--help" is not near the bunch of things there are described in the complete documentation.

(for those who don't know, the full manual can be read with `info gdb` - `man gdb` is only a short help)

People have been ignoring info for almost exactly as long as the FSF has been trying to supersede man with it.

Yes. The GNU manuals tend to be excellent sources. GNU Make's is particularly great. https://www.gnu.org/software/make/manual/make.html