followup to r332730/r332752: set kdb_why to "trap" for fatal traps

This change updates arm, arm64 and mips achitectures.  Additionally, it
removes redundant checks for kdb_active where it already results in
kdb_reenter() and adds kdb_reenter() calls where they were missing.

Some architectures check the return value of kdb_trap(), but some don't.
I haven't changed any of that.

Some trap handling routines have a return code.  I am not sure if I
provided correct ones for returns after kdb_reenter().  kdb_reenter
should never return unless kdb_jmpbufp is NULL for some reason.

Only compile tested for all affected architectures.  There can be bugs
resulting from my poor understanding of architecture specific details.

Reported by:	jhb
Reviewed by:	jhb, eadler
MFC after:	4 weeks
Differential Revision: https://reviews.freebsd.org/D15431

1 files changed, 10 insertions, 2 deletions

diff --git a/sys/arm64/arm64/trap.c b/sys/arm64/arm64/trap.c
index 71237bb98e4f..e0f2f448c445 100644
--- a/sys/arm64/arm64/trap.c
+++ b/sys/arm64/arm64/trap.c
@@ -156,6 +156,9 @@ data_abort(struct thread *td, struct trapframe *frame, uint64_t esr,
 	vm_prot_t ftype;
 	vm_offset_t va;
 	int error, sig, ucode;
+#ifdef KDB
+	bool handled;
+#endif
 
 	/*
 	 * According to the ARMv8-A rev. A.g, B2.10.5 "Load-Exclusive
@@ -226,9 +229,14 @@ data_abort(struct thread *td, struct trapframe *frame, uint64_t esr,
 			printf(" esr:         %.8lx\n", esr);
 
 #ifdef KDB
-			if (debugger_on_panic || kdb_active)
-				if (kdb_trap(ESR_ELx_EXCEPTION(esr), 0, frame))
+			if (debugger_on_panic) {
+				kdb_why = KDB_WHY_TRAP;
+				handled = kdb_trap(ESR_ELx_EXCEPTION(esr), 0,
+				    frame);
+				kdb_why = KDB_WHY_UNSET;
+				if (handled)
 					return;
+			}
 #endif
 			panic("vm_fault failed: %lx", frame->tf_elr);
 		}