[src/trunk]: src/common/lib/libc/arch/aarch64/string Fix a broken corner case...

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

details:   https://anonhg.NetBSD.org/src/rev/c45ce61e8df8
branches:  trunk
changeset: 938293:c45ce61e8df8
user:      jakllsch <jakllsch%NetBSD.org@localhost>
date:      Sat Sep 05 20:24:43 2020 +0000

description:
Fix a broken corner case of strlen()/strnlen() on aarch64eb

Previously a string such as "\x1\x1\x1\x1\x1\x1\x1" would count as
0 instead of 7 on BE.

diffstat:

 common/lib/libc/arch/aarch64/string/strlen.S |  14 ++++++++++----
 1 files changed, 10 insertions(+), 4 deletions(-)

diffs (36 lines):

diff -r 8f11a8dd6238 -r c45ce61e8df8 common/lib/libc/arch/aarch64/string/strlen.S
--- a/common/lib/libc/arch/aarch64/string/strlen.S      Sat Sep 05 19:17:42 2020 +0000
+++ b/common/lib/libc/arch/aarch64/string/strlen.S      Sat Sep 05 20:24:43 2020 +0000
@@ -1,4 +1,4 @@
-/* $NetBSD: strlen.S,v 1.3 2018/08/01 17:09:26 ryo Exp $ */
+/* $NetBSD: strlen.S,v 1.4 2020/09/05 20:24:43 jakllsch Exp $ */
 
 /*-
  * Copyright (c) 2014 The NetBSD Foundation, Inc.
@@ -31,7 +31,7 @@
 
 #include <machine/asm.h>
 
-RCSID("$NetBSD: strlen.S,v 1.3 2018/08/01 17:09:26 ryo Exp $")
+RCSID("$NetBSD: strlen.S,v 1.4 2020/09/05 20:24:43 jakllsch Exp $")
 
 #ifdef STRNLEN
 #define FUNCNAME       strnlen
@@ -96,9 +96,15 @@
        /*
         * We know there is a NUL in this dword.  Use clz to find it.
         */
-#ifdef __AARCH64EL__
+#ifdef __AARCH64EB__
+       /* avoid BE problem due to carry propagation if last non-NUL is \x01 */
+       ldr     x7, [x4, #-8]           /* reload dword */
+       rev     x7, x7                  /* byte swap */
+       sub     x6, x7, x11             /* a = X - 1 */
+       orr     x7, x7, #MASK8_0x7f     /* b = X | 0x7f */
+       bic     x6, x6, x7              /* a & ~b */
+#endif
        rev     x6, x6                  /* convert to BE */
-#endif
        clz     x6, x6                  /* find null byte */
        add     x0, x0, x6, lsr #3      /* add offset to the length */