[rfc] a few kern.mk and bsd.sys.mk related changes

[Bruce Cran]

On Sat, May 28, 2011 at 06:23:26PM +0000, Alexander Best wrote:
> 
> well i'm not an expert on this. but are we 100% sure that a kernel on amd64
> compiled with -O2 frename-registers can be debugged the same way as one with
> -O? if that is the case: sure...-O2 is fine. ;)
> 
> however i've often read messages - mostly by bruce evans - claiming that
> anything greater than -O will in fact decrease a kernel's ability to be
> debugged just as well as a kernel with -O.
> 

The critical option when -O2 is used is -fno-omit-frame-pointers, since removing
frame pointers makes debugging impossible (on i386). With -O2 code is moved around and
removed, so debugging is more difficult, but can still provide useful
information.

-- 
Bruce Cran