[src/trunk]: src/sys/arch/aarch64/aarch64 aarch64: Fix stack traces from jump...

[riastradh <riastradh%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/c099e02d905c
branches:  trunk
changeset: 1026511:c099e02d905c
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Sat Nov 27 14:11:04 2021 +0000

description:
aarch64: Fix stack traces from jump-to-null.

diffstat:

 sys/arch/aarch64/aarch64/db_trace.c |  21 +++++++++++++++++----
 1 files changed, 17 insertions(+), 4 deletions(-)

diffs (42 lines):

diff -r 22dbddc06c4e -r c099e02d905c sys/arch/aarch64/aarch64/db_trace.c
--- a/sys/arch/aarch64/aarch64/db_trace.c       Sat Nov 27 10:00:01 2021 +0000
+++ b/sys/arch/aarch64/aarch64/db_trace.c       Sat Nov 27 14:11:04 2021 +0000
@@ -1,4 +1,4 @@
-/* $NetBSD: db_trace.c,v 1.13 2020/12/11 18:03:33 skrll Exp $ */
+/* $NetBSD: db_trace.c,v 1.14 2021/11/27 14:11:04 riastradh Exp $ */
 
 /*
  * Copyright (c) 2017 Ryo Shimizu <ryo%nerv.org@localhost>
@@ -28,7 +28,7 @@
 
 #include <sys/cdefs.h>
 
-__KERNEL_RCSID(0, "$NetBSD: db_trace.c,v 1.13 2020/12/11 18:03:33 skrll Exp $");
+__KERNEL_RCSID(0, "$NetBSD: db_trace.c,v 1.14 2021/11/27 14:11:04 riastradh Exp $");
 
 #include <sys/param.h>
 #include <sys/proc.h>
@@ -302,8 +302,21 @@
                        lastfp = (uint64_t)tf;
                        lastlr = lr;
                        lr = fp = 0;
-                       db_read_bytes((db_addr_t)&tf->tf_pc, sizeof(lr), (char *)&lr);
-                       db_read_bytes((db_addr_t)&tf->tf_reg[29], sizeof(fp), (char *)&fp);
+                       db_read_bytes((db_addr_t)&tf->tf_pc, sizeof(lr),
+                           (char *)&lr);
+                       if (lr == 0) {
+                               /*
+                                * The exception may have been from a
+                                * jump to null, so the null pc we
+                                * would return to is useless.  Try
+                                * x[30] instead -- that will be the
+                                * return address for the jump.
+                                */
+                               db_read_bytes((db_addr_t)&tf->tf_reg[30],
+                                   sizeof(lr), (char *)&lr);
+                       }
+                       db_read_bytes((db_addr_t)&tf->tf_reg[29], sizeof(fp),
+                           (char *)&fp);
                        lr = aarch64_strip_pac(lr);
 
                        /*