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

[Alexander Best]

On Sat May 28 11, Pan Tsu wrote:
> Alexander Best <arundel at freebsd.org> writes:
> 
> > On Fri May 27 11, Alexander Best wrote:
> >> On Fri May 27 11, Warner Losh wrote:
> >> > These look generally good.  Just one thing I had a question on:
> >> > 
> >> >  #
> >> > +# Enable FreeBSD kernel-specific printf format specifiers. Also instruct gcc to
> >> > +# enable some diagnostics, which make it easier to pinpoint tinderbox failures.
> >> > +CFLAGS+=	-fformat-extensions -fdiagnostics-show-option
> >> > +
> >> > 
> >> > Does this put sand in the gears of clang support?
> >
> > i've improved the above comment so as to note that clang won't be affected by
> > -fdiagnostics-show-option. the new patch is available here:
> >
> > http://people.freebsd.org/~arundel/patches/kern.mk-bsy.sys.mk.patch
> >
> > another "issue" i've come across is the fact that on amd64, -O2 is always being
> > set, no matter, if debugging is enabled or disabled. i think amd64 should also
> > (just like all the other archs) be using -O, when debugging was enabled.
> 
> Any reason a kernel with symbols (DEBUG) *must* be pessimized to -O1 level?
> Looking at r140606 it's not clear how symbols are related to a bump
> from -O1 to -O2 for non-amd64 archs. And -RELEASE kernels since at least
> 6.0R have `makeoptions DEBUG=-g' uncommented in GENERIC.

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.

cheers.
alex

> 
> > changing this is quite easy. so if people think this is something worth
> > changing i can integrate it into my existing patch.

-- 
a13x