Attempt to make break-to-debugger and alternative break-to-debugger more

accessible:

(1) Always compile in support for breaking into the debugger if options
    KDB is present in the kernel.

(2) Disable both by default, but allow them to be enabled via tunables
    and sysctls debug.kdb.break_to_debugger and
    debug.kdb.alt_break_to_debugger.

(3) options BREAK_TO_DEBUGGER and options ALT_BREAK_TO_DEBUGGER continue
    to behave as before -- only now instead of compiling in
    break-to-debugger support, they change the default values of the
    above sysctls to enable those features by default.  Current kernel
    configurations should, therefore, continue to behave as expected.

(4) Migrate alternative break-to-debugger state machine logic out of
    individual device drivers into centralised KDB code.  This has a
    number of upsides, but also one downside: it's now tricky to release
    sio spin locks when entering the debugger, so we don't.  However,
    similar logic does not exist in other device drivers, including uart.

(5) dcons requires some special handling; unlike other console types, it
    allows overriding KDB's own debugger selection, so we need a new
    interface to KDB to allow that to work.

GENERIC kernels in -CURRENT will now support break-to-debugger as long as
appropriate boot/run-time options are set, which should improve the
debuggability of BETA kernels significantly.

MFC after:	3 weeks
Reviewed by:	kib, nwhitehorn
Approved by:	re (bz)

1 files changed, 2 insertions, 0 deletions

diff --git a/sys/sys/kdb.h b/sys/sys/kdb.h
index 2982e03c75f1..61ee0973eb14 100644
--- a/sys/sys/kdb.h
+++ b/sys/sys/kdb.h
@@ -64,6 +64,8 @@ extern struct pcb *kdb_thrctx;		/* Current context. */
 extern struct thread *kdb_thread;	/* Current thread. */
 
 int	kdb_alt_break(int, int *);
+int	kdb_alt_break_gdb(int, int *);
+int	kdb_break(void);
 void	kdb_backtrace(void);
 int	kdb_dbbe_select(const char *);
 void	kdb_enter(const char *, const char *);