[glibc/arm/gcs] aarch64: mark swapcontext with indirect_return

[Szabolcs Nagy <nsz@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=99f884d57f17afea877006284f469747711e1d51

commit 99f884d57f17afea877006284f469747711e1d51
Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date:   Thu Dec 28 15:53:38 2023 +0000

    aarch64: mark swapcontext with indirect_return

Diff:
---
 sysdeps/aarch64/bits/indirect-return.h | 36 ++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/sysdeps/aarch64/bits/indirect-return.h b/sysdeps/aarch64/bits/indirect-return.h
new file mode 100644
index 0000000000..99905f21fa
--- /dev/null
+++ b/sysdeps/aarch64/bits/indirect-return.h
@@ -0,0 +1,36 @@
+/* Definition of __INDIRECT_RETURN.  AArch64 version.
+   Copyright (C) 2024 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/>.  */
+
+#ifndef _UCONTEXT_H
+# error "Never include <bits/indirect-return.h> directly; use <ucontext.h> instead."
+#endif
+
+/* __INDIRECT_RETURN indicates that swapcontext may return via
+   an indirect branch.  This happens when GCS is enabled, so
+   add the attribute if available, otherwise returns_twice has
+   a similar effect, but it prevents some code transformations
+   that can cause build failures in some rare cases so it is
+   only used when GCS is enabled.  */
+#if __glibc_has_attribute (__indirect_return__)
+# define __INDIRECT_RETURN __attribute__ ((__indirect_return__))
+#elif __glibc_has_attribute (__returns_twice__) \
+      && defined __ARM_FEATURE_GCS_DEFAULT
+# define __INDIRECT_RETURN __attribute__ ((__returns_twice__))
+#else
+# define __INDIRECT_RETURN
+#endif