[glibc/arm/morello/main] aarch64: morello: purecap rawmemchr

[Szabolcs Nagy <nsz@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=61c8e4890382f52761cd2821f71e8021c744a39d

commit 61c8e4890382f52761cd2821f71e8021c744a39d
Author: Carlos Eduardo Seo <carlos.seo@arm.com>
Date:   Mon Jul 12 15:06:26 2021 -0300

    aarch64: morello: purecap rawmemchr
    
    Modified rawmemchr to support Arm Morello Capabilities.

Diff:
---
 sysdeps/aarch64/morello/rawmemchr.S | 43 +++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

diff --git a/sysdeps/aarch64/morello/rawmemchr.S b/sysdeps/aarch64/morello/rawmemchr.S
new file mode 100644
index 0000000000..10e89ee6b7
--- /dev/null
+++ b/sysdeps/aarch64/morello/rawmemchr.S
@@ -0,0 +1,43 @@
+/* rawmemchr - find a character in a memory zone
+
+   Copyright (C) 2022 Free Software Foundation, Inc.
+
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library.  If not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <sysdep.h>
+
+/* Special case rawmemchr (s, 0) as strlen, otherwise tailcall memchr.
+   Call strlen without setting up a full frame - it preserves x14/x15.
+*/
+
+ENTRY (__rawmemchr)
+
+	cbz	w1, L(do_strlen)
+	mov	x2, -1
+	b	__memchr
+
+L(do_strlen):
+	mov	c15, c30
+	cfi_return_column (c15)
+	mov	c14, c0
+	bl	__strlen
+	add	c0, c14, x0
+	ret	c15
+
+END (__rawmemchr)
+weak_alias (__rawmemchr, rawmemchr)
+libc_hidden_builtin_def (__rawmemchr)