GDB is free software,
protected by the GNU
General Public License (GPL). The GPL gives you the freedom to copy
or adapt a licensed program—but every person getting a copy also gets with
it the freedom to modify that copy (which means that they must get access
to the source code), and the freedom to distribute further copies. Typical
software companies use copyrights to limit your freedoms; the Free Software
Foundation uses the GPL to preserve these freedoms. Fundamentally, the
General Public License is a license which says that you have these freedoms
and that you cannot take these freedoms away from anyone else.