mips,kgdb: kdb low level trap catch and stack trace

The only way the debugger can handle a trap in inside rcu_lock,
notify_die, or atomic_notifier_call_chain without a recursive fault is
to have a low level "first opportunity handler" do_trap_or_bp() handler.

Generally this will be something the vast majority of folks will not
need, but for those who need it, it is added as a kernel .config
option called KGDB_LOW_LEVEL_TRAP.

Also added was a die notification for oops such that kdb can catch an
oops for analysis.

There appeared to be no obvious way to pass the struct pt_regs from
the original exception back to the stack back tracer, so a special
case was added to show_stack() for when kdb is active because you
generally desire to generally look at the back trace of the original
exception.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Acked-by: Ralf Baechle <ralf@linux-mips.org>

1 files changed, 21 insertions, 1 deletions

diff --git a/arch/mips/kernel/kgdb.c b/arch/mips/kernel/kgdb.c
index 6ed4c83c869b..9b78ff6e9b84 100644
--- a/arch/mips/kernel/kgdb.c
+++ b/arch/mips/kernel/kgdb.c
@@ -203,7 +203,7 @@ static int kgdb_mips_notify(struct notifier_block *self, unsigned long cmd,
         if (atomic_read(&kgdb_active) != -1)
                 kgdb_nmicallback(smp_processor_id(), regs);
 
-        if (kgdb_handle_exception(trap, compute_signal(trap), 0, regs))
+        if (kgdb_handle_exception(trap, compute_signal(trap), cmd, regs))
                 return NOTIFY_DONE;
 
         if (atomic_read(&kgdb_setting_breakpoint))
@@ -217,6 +217,26 @@ static int kgdb_mips_notify(struct notifier_block *self, unsigned long cmd,
         return NOTIFY_STOP;
 }
 
+#ifdef CONFIG_KGDB_LOW_LEVEL_TRAP
+int kgdb_ll_trap(int cmd, const char *str,
+                 struct pt_regs *regs, long err, int trap, int sig)
+{
+        struct die_args args = {
+                .regs   = regs,
+                .str    = str,
+                .err    = err,
+                .trapnr = trap,
+                .signr  = sig,
+
+        };
+
+        if (!kgdb_io_module_registered)
+                return NOTIFY_DONE;
+
+        return kgdb_mips_notify(NULL, cmd, &args);
+}
+#endif /* CONFIG_KGDB_LOW_LEVEL_TRAP */
+
 static struct notifier_block kgdb_notifier = {
         .notifier_call = kgdb_mips_notify,
 };