1 /* Definition of __INDIRECT_RETURN.  x86 version.
2    Copyright (C) 2018-2021 Free Software Foundation, Inc.
3    This file is part of the GNU C Library.
4 
5    The GNU C Library is free software; you can redistribute it and/or
6    modify it under the terms of the GNU Lesser General Public
7    License as published by the Free Software Foundation; either
8    version 2.1 of the License, or (at your option) any later version.
9 
10    The GNU C Library is distributed in the hope that it will be useful,
11    but WITHOUT ANY WARRANTY; without even the implied warranty of
12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
13    Lesser General Public License for more details.
14 
15    You should have received a copy of the GNU Lesser General Public
16    License along with the GNU C Library; if not, see
17    <https://www.gnu.org/licenses/>.  */
18 
19 #ifndef _UCONTEXT_H
20 # error "Never include <bits/indirect-return.h> directly; use <ucontext.h> instead."
21 #endif
22 
23 /* On x86, swapcontext returns via indirect branch when the shadow stack
24    is enabled.  Define __INDIRECT_RETURN to indicate whether swapcontext
25    returns via indirect branch.  */
26 #if defined __CET__ && (__CET__ & 2) != 0
27 # if __glibc_has_attribute (__indirect_return__)
28 #  define __INDIRECT_RETURN __attribute__ ((__indirect_return__))
29 # else
30 /* Newer compilers provide the indirect_return attribute, but without
31    it we can use returns_twice to affect the optimizer in the same
32    way and avoid unsafe optimizations.  */
33 #  define __INDIRECT_RETURN __attribute__ ((__returns_twice__))
34 # endif
35 #else
36 # define __INDIRECT_RETURN
37 #endif
38