Add <bits/indirect-return.h>
Commit Message
On Wed, Jul 18, 2018 at 1:58 PM, Joseph Myers <joseph@codesourcery.com> wrote:
> On Wed, 18 Jul 2018, H.J. Lu wrote:
>
>> +#ifndef __INDIRECT_RETURN
>> +# define __INDIRECT_RETURN
>> +#endif
>
> This default definition is missing a comment to define the semantics of
> this macro. And please avoid this #ifndef convention. Rather, the normal
> glibc convention would be to have e.g. a bits/indirect-return.h installed
> header, with a default version with an empty definition and a comment
> documenting the semantics, and a separate x86 version.
>
Here is the updated patch. I am running native tests on x86 and
scripts/build-many-glibcs.py now.
Thanks.
Comments
On Wed, 18 Jul 2018, H.J. Lu wrote:
> +/* __INDIRECT_RETURN is used on swapcontext() to indicate if it
As per the GNU Coding Standards, don't use () to indicate you're referring
to a function, only when referring to a function call with no arguments.
> +/* On x86, swapcontext() returns via indirect branch when the shadow
> + stack is enabled. Define __INDIRECT_RETURN to indicate if
> + swapcontext() returns via indirect branch. */
Likewise.
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>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
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.
* 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
new file mode 100644
@@ -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
@@ -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
@@ -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
@@ -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++)
new file mode 100644
@@ -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