If you’re getting messages in gdb like …
Cannot insert breakpoint
… and …
Temporarily disabling shared library breakpoints
… in Gentoo-hardened it might be because you have the Pax extensions installed as the following site indicates: http://www.gentoo.org/proj/en/hardened/hardenedfaq.xml#hardeneddebug. Solution is given in the link and another solution is of course running a non-hardened kernel while debugging.