Created attachment 151355 [details] patch vt(4) misses the ALT_BREAK_TO_DEBUGGER feature (at least in 9-STABLE but probably in all versions). This patch brings it back.
It looks like Ed committed this to head in r276282 but it was never merged.
A commit references this bug: Author: emaste Date: Thu Aug 13 19:48:20 UTC 2015 New revision: 286742 URL: https://svnweb.freebsd.org/changeset/base/286742 Log: MFC r276282: Support ALT_BREAK_TO_DEBUGGER in vt(4) PR: 196511 Changes: _U stable/10/ stable/10/sys/dev/vt/vt.h stable/10/sys/dev/vt/vt_core.c
A commit references this bug: Author: emaste Date: Thu Aug 13 19:51:23 UTC 2015 New revision: 286743 URL: https://svnweb.freebsd.org/changeset/base/286743 Log: MFC r276282: Support ALT_BREAK_TO_DEBUGGER in vt(4) PR: 196511 Changes: _U stable/9/sys/ _U stable/9/sys/dev/ stable/9/sys/dev/vt/vt.h stable/9/sys/dev/vt/vt_core.c
Merge to HEAD in r276282, stable/10 in r286742 and stable/9 in r286743