From c9c4d38aa84d87a4d24a7857e98bfa7b6dff1f68 Mon Sep 17 00:00:00 2001
From: Andriy Gapon <avg@FreeBSD.org>
Date: Wed, 16 May 2018 06:52:08 +0000
Subject: [PATCH] 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
---
 sys/arm/arm/trap-v4.c  | 17 +++++++++++++++--
 sys/arm/arm/trap-v6.c  |  5 ++++-
 sys/arm64/arm64/trap.c | 12 ++++++++++--
 sys/mips/mips/trap.c   | 11 +++++++++--
 4 files changed, 38 insertions(+), 7 deletions(-)

diff --git a/sys/arm/arm/trap-v4.c b/sys/arm/arm/trap-v4.c
index bec22abf0dcd..3ee730432e75 100644
--- a/sys/arm/arm/trap-v4.c
+++ b/sys/arm/arm/trap-v4.c
@@ -404,7 +404,16 @@ dab_fatal(struct trapframe *tf, u_int fsr, u_int far, struct thread *td,
     struct ksig *ksig)
 {
 	const char *mode;
+#ifdef KDB
+	bool handled;
+#endif
 
+#ifdef KDB
+	if (kdb_active) {
+		kdb_reenter();
+		return (0);
+	}
+#endif
 #ifdef KDTRACE_HOOKS
 	if (!TRAP_USERMODE(tf))	{
 		if (dtrace_trap_func != NULL && (*dtrace_trap_func)(tf, far & FAULT_TYPE_MASK))
@@ -447,9 +456,13 @@ dab_fatal(struct trapframe *tf, u_int fsr, u_int far, struct thread *td,
 	printf(", pc =%08x\n\n", tf->tf_pc);
 
 #ifdef KDB
-	if (debugger_on_panic || kdb_active)
-		if (kdb_trap(fsr, 0, tf))
+	if (debugger_on_panic) {
+		kdb_why = KDB_WHY_TRAP;
+		handled = kdb_trap(fsr, 0, tf);
+		kdb_why = KDB_WHY_UNSET;
+		if (handled)
 			return (0);
+	}
 #endif
 	panic("Fatal abort");
 	/*NOTREACHED*/
diff --git a/sys/arm/arm/trap-v6.c b/sys/arm/arm/trap-v6.c
index d3efc0c0ee53..ae78401e91a3 100644
--- a/sys/arm/arm/trap-v6.c
+++ b/sys/arm/arm/trap-v6.c
@@ -599,8 +599,11 @@ abort_fatal(struct trapframe *tf, u_int idx, u_int fsr, u_int far,
 	printf(", pc =%08x\n\n", tf->tf_pc);
 
 #ifdef KDB
-	if (debugger_on_panic || kdb_active)
+	if (debugger_on_panic) {
+		kdb_why = KDB_WHY_TRAP;
 		kdb_trap(fsr, 0, tf);
+		kdb_why = KDB_WHY_UNSET;
+	}
 #endif
 	panic("Fatal abort");
 	/*NOTREACHED*/
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);
 		}
diff --git a/sys/mips/mips/trap.c b/sys/mips/mips/trap.c
index a796c6bd8ccb..746208e521fd 100644
--- a/sys/mips/mips/trap.c
+++ b/sys/mips/mips/trap.c
@@ -530,7 +530,12 @@ trap(struct trapframe *trapframe)
 	register_t *frame_regs;
 
 	trapdebug_enter(trapframe, 0);
-	
+#ifdef KDB
+	if (kdb_active) {
+		kdb_reenter();
+		return (0);
+	}
+#endif
 	type = (trapframe->cause & MIPS_CR_EXC_CODE) >> MIPS_CR_EXC_CODE_SHIFT;
 	if (TRAPF_USERMODE(trapframe)) {
 		type |= T_USER;
@@ -1095,8 +1100,10 @@ trap(struct trapframe *trapframe)
 #endif
 
 #ifdef KDB
-		if (debugger_on_panic || kdb_active) {
+		if (debugger_on_panic) {
+			kdb_why = KDB_WHY_TRAP;
 			kdb_trap(type, 0, trapframe);
+			kdb_why = KDB_WHY_UNSET;
 		}
 #endif
 		panic("trap");