sysdeps/x86/bits/indirect-return.h

   1 /* Definition of __INDIRECT_RETURN.  x86 version.
   2    Copyright (C) 2018-2019 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    <http://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