Fix DDB to unwind across exception frames.

While here, add an extra line of information for exceptions and
interrupts and compress the per-frame line down to one line to match
other architectures.

Reviewed by:	mhorne, br
MFC after:	1 week
Sponsored by:	DARPA
Differential Revision:	https://reviews.freebsd.org/D23508

sys/riscv/riscv/db_trace.c

@@ -2,6 +2,7 @@
  * Copyright (c) 2015 The FreeBSD Foundation
  * Copyright (c) 2016 Ruslan Bukin <[email protected]>
  * All rights reserved.
+ * Copyright (c) 2020 John Baldwin <[email protected]>
  *
  * Portions of this software were developed by Semihalf under
  * the sponsorship of the FreeBSD Foundation.
@@ -38,15 +39,18 @@
 
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
+
 #include <sys/param.h>
-#include <sys/proc.h>
 #include <sys/kdb.h>
-#include <machine/pcb.h>
+#include <sys/proc.h>
+
 #include <ddb/ddb.h>
 #include <ddb/db_sym.h>
 
+#include <machine/pcb.h>
 #include <machine/riscvreg.h>
 #include <machine/stack.h>
+#include <machine/vmparam.h>
 
 void
 db_md_list_watchpoints()
@@ -80,9 +84,6 @@ db_stack_trace_cmd(struct unwind_state *frame)
 	while (1) {
 		pc = frame->pc;
 
-		if (unwind_frame(frame) < 0)
-			break;
-
 		sym = db_search_symbol(pc, DB_STGY_ANY, &offset);
 		if (sym == C_DB_SYM_NULL) {
 			value = 0;
@@ -94,11 +95,32 @@ db_stack_trace_cmd(struct unwind_state *frame)
 		db_printsym(frame->pc, DB_STGY_PROC);
 		db_printf("\n");
 
-		db_printf("\t pc = 0x%016lx ra = 0x%016lx\n",
-		    pc, frame->pc);
-		db_printf("\t sp = 0x%016lx fp = 0x%016lx\n",
-		    frame->sp, frame->fp);
-		db_printf("\n");
+		if (strcmp(name, "cpu_exception_handler_supervisor") == 0 ||
+		    strcmp(name, "cpu_exception_handler_user") == 0) {
+			struct trapframe *tf;
+
+			tf = (struct trapframe *)(uintptr_t)frame->sp;
+
+			if (tf->tf_scause & EXCP_INTR)
+				db_printf("--- interrupt %ld\n",
+				    tf->tf_scause & EXCP_MASK);
+			else
+				db_printf("--- exception %ld, tval = %#lx\n",
+				    tf->tf_scause & EXCP_MASK,
+				    tf->tf_stval);
+			frame->sp = (uint64_t)tf->tf_sp;
+			frame->fp = (uint64_t)tf->tf_s[0];
+			frame->pc = (uint64_t)tf->tf_sepc;
+			if (!INKERNEL(frame->fp))
+				break;
+			continue;
+		}
+
+		if (strcmp(name, "fork_trampoline") == 0)
+			break;
+
+		if (unwind_frame(frame) < 0)
+			break;
 	}
 }