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Add <bits/indirect-return.h> and include it in <ucontext.h>. __INDIRECT_RETURN defined in <bits/indirect-return.h> indicates if swapcontext requires special compiler treatment. The default __INDIRECT_RETURN is empty. On x86, when shadow stack is enabled, __INDIRECT_RETURN is defined with indirect_return attribute, which has been added to GCC 9, to indicate that swapcontext returns via indirect branch. Otherwise __INDIRECT_RETURN is defined with returns_twice attribute. When shadow stack is enabled, remove always_inline attribute from prepare_test_buffer in string/tst-xbzero-opt.c to avoid: tst-xbzero-opt.c: In function ‘prepare_test_buffer’: tst-xbzero-opt.c:105:1: error: function ‘prepare_test_buffer’ can never be inlined because it uses setjmp prepare_test_buffer (unsigned char *buf) when indirect_return attribute isn't available. Reviewed-by: Carlos O'Donell <carlos@redhat.com> * bits/indirect-return.h: New file. * misc/sys/cdefs.h (__glibc_has_attribute): New. * sysdeps/x86/bits/indirect-return.h: Likewise. * stdlib/Makefile (headers): Add bits/indirect-return.h. * stdlib/ucontext.h: Include <bits/indirect-return.h>. (swapcontext): Add __INDIRECT_RETURN. * string/tst-xbzero-opt.c (ALWAYS_INLINE): New. (prepare_test_buffer): Use it.
38 lines
1.5 KiB
C
38 lines
1.5 KiB
C
/* Definition of __INDIRECT_RETURN. x86 version.
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Copyright (C) 2018 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#ifndef _UCONTEXT_H
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# error "Never include <bits/indirect-return.h> directly; use <ucontext.h> instead."
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#endif
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/* On x86, swapcontext returns via indirect branch when the shadow stack
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is enabled. Define __INDIRECT_RETURN to indicate whether swapcontext
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returns via indirect branch. */
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#if defined __CET__ && (__CET__ & 2) != 0
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# if __glibc_has_attribute (__indirect_return__)
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# define __INDIRECT_RETURN __attribute__ ((__indirect_return__))
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# else
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/* Newer compilers provide the indirect_return attribute, but without
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it we can use returns_twice to affect the optimizer in the same
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way and avoid unsafe optimizations. */
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# define __INDIRECT_RETURN __attribute__ ((__returns_twice__))
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# endif
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#else
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# define __INDIRECT_RETURN
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#endif
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