[src/trunk]: src/sys/ddb Avoids signedness bit shift in db_get_value()

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

details:   https://anonhg.NetBSD.org/src/rev/5a872717aeed
branches:  trunk
changeset: 1002994:5a872717aeed
user:      kamil <kamil%NetBSD.org@localhost>
date:      Fri Aug 23 14:48:50 2019 +0000

description:
Avoids signedness bit shift in db_get_value()

Appease UBSan.

diffstat:

 sys/ddb/db_access.c |  11 +++++++----
 1 files changed, 7 insertions(+), 4 deletions(-)

diffs (42 lines):

diff -r 478c9af416c9 -r 5a872717aeed sys/ddb/db_access.c
--- a/sys/ddb/db_access.c       Fri Aug 23 14:12:39 2019 +0000
+++ b/sys/ddb/db_access.c       Fri Aug 23 14:48:50 2019 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: db_access.c,v 1.23 2018/02/04 09:17:54 mrg Exp $       */
+/*     $NetBSD: db_access.c,v 1.24 2019/08/23 14:48:50 kamil Exp $     */
 
 /*
  * Mach Operating System
@@ -30,7 +30,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: db_access.c,v 1.23 2018/02/04 09:17:54 mrg Exp $");
+__KERNEL_RCSID(0, "$NetBSD: db_access.c,v 1.24 2019/08/23 14:48:50 kamil Exp $");
 
 #if defined(_KERNEL_OPT)
 #include "opt_kgdb.h"
@@ -59,18 +59,21 @@
 db_get_value(db_addr_t addr, size_t size, bool is_signed)
 {
        char data[sizeof(db_expr_t)] __aligned(sizeof(db_expr_t));
+       uintmax_t uvalue;
        db_expr_t value;
        size_t i;
 
        db_read_bytes(addr, size, data);
 
-       value = 0;
+       uvalue = 0;
 #if BYTE_ORDER == LITTLE_ENDIAN
        for (i = size; i-- > 0;)
 #else /* BYTE_ORDER == BIG_ENDIAN */
        for (i = 0; i < size; i++)
 #endif /* BYTE_ORDER */
-               value = (value << 8) + (data[i] & 0xFF);
+               uvalue = (uvalue << 8) + (data[i] & 0xFF);
+
+       value = (db_expr_t)uvalue;
 
        if (size < sizeof(db_expr_t) && is_signed
            && (value & ((db_expr_t)1 << (8*size - 1)))) {