From 1345e8591ebc4ed6a97f228a1c0b49c9ce21339b Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Thu, 7 Jun 2018 20:50:11 -0700
Subject: [PATCH] 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 â€˜prepare_test_bufferâ€™:
tst-xbzero-opt.c:105:1: error: function â€˜prepare_test_bufferâ€™ can never be inlined because it uses setjmp
 prepare_test_buffer (unsigned char *buf)

when indirect_return attribute isn't available.

	* bits/indirect-return.h: New file.
	* 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.
---
 bits/indirect-return.h             | 25 +++++++++++++++++++++
 stdlib/Makefile                    |  2 +-
 stdlib/ucontext.h                  |  6 ++++-
 string/tst-xbzero-opt.c            | 10 ++++++++-
 sysdeps/x86/bits/indirect-return.h | 36 ++++++++++++++++++++++++++++++
 5 files changed, 76 insertions(+), 3 deletions(-)
 create mode 100644 bits/indirect-return.h
 create mode 100644 sysdeps/x86/bits/indirect-return.h

diff --git a/bits/indirect-return.h b/bits/indirect-return.h
new file mode 100644
index 0000000000..f309e160e7
--- /dev/null
+++ b/bits/indirect-return.h
@@ -0,0 +1,25 @@
+/* Definition of __INDIRECT_RETURN.  Generic version.
+   Copyright (C) 2018 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
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef _UCONTEXT_H
+# error "Never include <bits/indirect-return.h> directly; use <ucontext.h> instead."
+#endif
+
+/* __INDIRECT_RETURN is used on swapcontext() to indicate if it
+   requires special compiler treatment.  */
+#define __INDIRECT_RETURN
diff --git a/stdlib/Makefile b/stdlib/Makefile
index 808a8ceab7..b5e55b0a55 100644
--- a/stdlib/Makefile
+++ b/stdlib/Makefile
@@ -26,7 +26,7 @@ headers	:= stdlib.h bits/stdlib.h bits/stdlib-ldbl.h bits/stdlib-float.h      \
 	   monetary.h bits/monetary-ldbl.h				      \
 	   inttypes.h stdint.h bits/wordsize.h				      \
 	   errno.h sys/errno.h bits/errno.h bits/types/error_t.h	      \
-	   ucontext.h sys/ucontext.h					      \
+	   ucontext.h sys/ucontext.h bits/indirect-return.h		      \
 	   alloca.h fmtmsg.h						      \
 	   bits/stdlib-bsearch.h sys/random.h bits/stdint-intn.h	      \
 	   bits/stdint-uintn.h
diff --git a/stdlib/ucontext.h b/stdlib/ucontext.h
index eec7611631..ec630038f6 100644
--- a/stdlib/ucontext.h
+++ b/stdlib/ucontext.h
@@ -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
diff --git a/string/tst-xbzero-opt.c b/string/tst-xbzero-opt.c
index cf7041f37a..d49ddef9ae 100644
--- a/string/tst-xbzero-opt.c
+++ b/string/tst-xbzero-opt.c
@@ -100,7 +100,15 @@ static ucontext_t uc_main, uc_co;
 /* Always check the test buffer immediately after filling it; this
    makes externally visible side effects depend on the buffer existing
    and having been filled in.  */
-static inline __attribute__  ((always_inline)) void
+#if defined __CET__ && !__GNUC_PREREQ (9, 0)
+/* Note: swapcontext returns via indirect branch when SHSTK is enabled.
+   Without indirect_return attribute in GCC 9, swapcontext is marked
+   with returns_twice attribute, which prevents always_inline to work.  */
+# define ALWAYS_INLINE
+#else
+# define ALWAYS_INLINE	__attribute__  ((always_inline))
+#endif
+static inline ALWAYS_INLINE void
 prepare_test_buffer (unsigned char *buf)
 {
   for (unsigned int i = 0; i < PATTERN_REPS; i++)
diff --git a/sysdeps/x86/bits/indirect-return.h b/sysdeps/x86/bits/indirect-return.h
new file mode 100644
index 0000000000..96fa0d323d
--- /dev/null
+++ b/sysdeps/x86/bits/indirect-return.h
@@ -0,0 +1,36 @@
+/* Definition of __INDIRECT_RETURN.  x86 version.
+   Copyright (C) 2018 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
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef _UCONTEXT_H
+# error "Never include <bits/indirect-return.h> directly; use <ucontext.h> instead."
+#endif
+
+/* On x86, swapcontext() returns via indirect branch when the shadow
+   stack is enabled.  Define __INDIRECT_RETURN to indicate if
+   swapcontext() returns via indirect branch.  */
+#if defined __CET__ && (__CET__ & 2) != 0
+/* Note: Functions returned via indirect branch returns once.  Without
+   indirect_return attribute in GCC 9, use returns_twice attribute.  */
+# if __GNUC_PREREQ (9, 0)
+#  define __INDIRECT_RETURN __attribute__ ((__indirect_return__))
+# else
+#  define __INDIRECT_RETURN __attribute__ ((__returns_twice__))
+# endif
+#else
+# define __INDIRECT_RETURN
+#endif
-- 
2.17.1
