r265785 introduced kern.opts.mk for kernel options, but did not update make showconfig and/or tools/build/options/makeman, so a subsequent regeneration of src.conf.5 in r266158 removed the description for kernel options like MK_DEBUG_SYMBOLS A fix is fairly straightforward, but I'm not sure if there are plans to evolve the kernel/userland config so I'll let Warner choose the best fix.
Possible approach from Warner, - @${MAKE} -n -f src.opts.mk -V dummy -dg1 2>&1 | grep ^MK_ | sort + @(${MAKE} -n -f src.opts.mk -V dummy -dg1 2>&1; \ + ${MAKE} -n -f sys/conf/kern.opts.mk -V dummy -dg1 2>&1) | grep ^MK_ | sort
A commit references this bug: Author: imp Date: Tue Oct 21 20:29:51 UTC 2014 New revision: 273418 URL: https://svnweb.freebsd.org/changeset/base/273418 Log: Generate both userland and kernel option settings for showconfig. PR: 191920 Changes: head/Makefile.inc1
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