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Add <bits/indirect-return.h>

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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.
This commit is contained in:
H.J. Lu
2018-07-24 07:55:35 -07:00
parent 21526a507d
commit e27f41ba2b
7 changed files with 94 additions and 3 deletions
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6
stdlib/ucontext.h
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@ -22,6 +22,9 @@
#include <features.h>
/* Get definition of __INDIRECT_RETURN. */
#include <bits/indirect-return.h>
/* Get machine dependent definition of data structures. */
#include <sys/ucontext.h>
@ -36,7 +39,8 @@ extern int setcontext (const ucontext_t *__ucp) __THROWNL;
/* Save current context in context variable pointed to by OUCP and set
context from variable pointed to by UCP. */
extern int swapcontext (ucontext_t *__restrict __oucp,
const ucontext_t *__restrict __ucp) __THROWNL;
const ucontext_t *__restrict __ucp)
__THROWNL __INDIRECT_RETURN;
/* Manipulate user context UCP to continue with calling functions FUNC
and the ARGC-1 parameters following ARGC when the context is used