[PATCH v3] aarch64: Add split-stack TCB field

[Adhemerval Zanella <adhemerval dot zanella at linaro dot org>]

Changes from previous version [1]

  - Change the symbol exported by loader from a function to a data
    symbol (__libc_tcb_private_ss).  This allows binaries to fail at
    loading time instead of runtime on older glibc.

  - Fixed struct pthread alignment on TLS_PRE_TCB_SIZE.

--

This patch adds split-stack support pointer guard on glibc for aarch64.
Different from other architectures (powerpc, s390) where the memory is
placed on TCB, aarch64 one is placed bofore thread pointer initial
position.  It has an advantage over extending TCB because for aarch64
TLS variable placement take in consideration tcbhead_t size and by
changing its value would require to also update the static linker
(and it would also add incompatibility with glibc and older linkers).

For aarch64 tcb direct access is fastest for thread local variable on
all mode and related TLS access.  It requires just a direct load with
displacement of -8 (since thread pointer points to tcbhead_t).

It also adds a loader symbol (__tcb_private_ss) to signal de existence
of the split stack guard area.

Checked on aarch64-linux-gnu.

	* sysdeps/aarch64/Makefile [$(subdir) = elf] (sysdeps-dl-routines):
	Add tcb-version.
	* sysdeps/aarch64/Versions [ld] (GLIBC_2.26): Add
	__libc_tcb_private_ss.
	* sysdeps/aarch64/nptl/tls.h (tcbprehead_t): New struct.
	(TLS_PRE_TCB_SIZE): Take tcbprehead_t in consideration.
	(TLS_DEFINE_INIT_TP): Likewise.
	(THREAD_SELF): Likewise.
	(DB_THREAD_SELF): Likewise.
	* sysdeps/aarch64/tcb-version.c: New file.
	* sysdeps/unix/sysv/linux/aarch64/ld.abilist (GLIBC_2.26): Add.
	(__libc_tcb_private_ss): Likewise.
	* sysdeps/aarch64/nptl/tcb-offsets.sym (PTHREAD_SIZEOF): Rename to
	PTHREAD_PRE_TCB_SIZE.
	* sysdeps/unix/sysv/linux/aarch64/sysdep-cancel.h
	[!IS_IN (libprthread) && !IS_IN (libc) (SINGLE_THREAD_P): Use
	PTHREAD_PRE_TCB_SIZE instead of PTHREAD_SIZEOF.
---
 ChangeLog                                       | 20 ++++++++++++++++++++
 sysdeps/aarch64/Makefile                        |  2 +-
 sysdeps/aarch64/Versions                        |  8 ++++++++
 sysdeps/aarch64/nptl/tcb-offsets.sym            |  2 +-
 sysdeps/aarch64/nptl/tls.h                      | 25 ++++++++++++++++++++-----
 sysdeps/aarch64/tcb-version.c                   | 23 +++++++++++++++++++++++
 sysdeps/unix/sysv/linux/aarch64/ld.abilist      |  2 ++
 sysdeps/unix/sysv/linux/aarch64/sysdep-cancel.h |  2 +-
 8 files changed, 76 insertions(+), 8 deletions(-)
 create mode 100644 sysdeps/aarch64/tcb-version.c

diff --git a/sysdeps/aarch64/Makefile b/sysdeps/aarch64/Makefile
index 562c137..0155988 100644
--- a/sysdeps/aarch64/Makefile
+++ b/sysdeps/aarch64/Makefile
@@ -5,7 +5,7 @@ CFLAGS-backtrace.c += -funwind-tables
 endif
 
 ifeq ($(subdir),elf)
-sysdep-dl-routines += tlsdesc dl-tlsdesc
+sysdep-dl-routines += tlsdesc dl-tlsdesc tcb-version
 gen-as-const-headers += dl-link.sym
 endif
 
diff --git a/sysdeps/aarch64/Versions b/sysdeps/aarch64/Versions
index e1aa44f..da547a8 100644
--- a/sysdeps/aarch64/Versions
+++ b/sysdeps/aarch64/Versions
@@ -3,3 +3,11 @@ libc {
     _mcount;
   }
 }
+
+ld {
+  GLIBC_2.26 {
+    # Symbol used to version control the private GLIBC TCB split-stack
+    # field.
+    __libc_tcb_private_ss;
+  }
+}
diff --git a/sysdeps/aarch64/nptl/tcb-offsets.sym b/sysdeps/aarch64/nptl/tcb-offsets.sym
index 238647d..6004379 100644
--- a/sysdeps/aarch64/nptl/tcb-offsets.sym
+++ b/sysdeps/aarch64/nptl/tcb-offsets.sym
@@ -3,4 +3,4 @@
 
 PTHREAD_MULTIPLE_THREADS_OFFSET		offsetof (struct pthread, header.multiple_threads)
 PTHREAD_TID_OFFSET			offsetof (struct pthread, tid)
-PTHREAD_SIZEOF				sizeof (struct pthread)
+PTHREAD_PRE_TCB_SIZE			TLS_PRE_TCB_SIZE
diff --git a/sysdeps/aarch64/nptl/tls.h b/sysdeps/aarch64/nptl/tls.h
index 175df39..d7c8ea7 100644
--- a/sysdeps/aarch64/nptl/tls.h
+++ b/sysdeps/aarch64/nptl/tls.h
@@ -26,6 +26,7 @@
 # include <stddef.h>
 # include <stdint.h>
 # include <dl-dtv.h>
+# include <libc-internal.h>
 
 #else /* __ASSEMBLER__ */
 # include <tcb-offsets.h>
@@ -49,6 +50,12 @@ typedef struct
   void *private;
 } tcbhead_t;
 
+typedef struct
+{
+  /* GCC split stack support.  */
+  void *__private_ss;
+} tcbprehead_t;
+
 /* This is the size of the initial TCB.  */
 # define TLS_INIT_TCB_SIZE	sizeof (tcbhead_t)
 
@@ -58,8 +65,14 @@ typedef struct
 /* This is the size of the TCB.  */
 # define TLS_TCB_SIZE		sizeof (tcbhead_t)
 
-/* This is the size we need before TCB.  */
-# define TLS_PRE_TCB_SIZE	sizeof (struct pthread)
+/* This is the size we need before TCB.  Check if there is room for
+   tcbprehead_t in struct pthread's final padding and if not add it on
+   required pre-tcb size.  */
+# define TLS_PRE_TCB_SIZE \
+  (sizeof (struct pthread)						\
+   + (PTHREAD_STRUCT_END_PADDING < sizeof (tcbprehead_t)		\
+      ? ALIGN_UP (sizeof (tcbprehead_t), __alignof__ (struct pthread))	\
+      : 0))
 
 /* Alignment requirements for the TCB.  */
 # define TLS_TCB_ALIGN		__alignof__ (struct pthread)
@@ -84,7 +97,8 @@ typedef struct
   ({ __asm __volatile ("msr tpidr_el0, %0" : : "r" (tcbp)); NULL; })
 
 /* Value passed to 'clone' for initialization of the thread register.  */
-# define TLS_DEFINE_INIT_TP(tp, pd) void *tp = (pd) + 1
+# define TLS_DEFINE_INIT_TP(tp, pd) \
+  void *tp = (void*)((uintptr_t) (pd) + TLS_PRE_TCB_SIZE)
 
 /* Return the address of the dtv for the current thread.  */
 # define THREAD_DTV() \
@@ -92,11 +106,12 @@ typedef struct
 
 /* Return the thread descriptor for the current thread.  */
 # define THREAD_SELF \
- ((struct pthread *)__builtin_thread_pointer () - 1)
+  ((struct pthread *)((uintptr_t) __builtin_thread_pointer () \
+		      - TLS_PRE_TCB_SIZE))
 
 /* Magic for libthread_db to know how to do THREAD_SELF.  */
 # define DB_THREAD_SELF \
-  CONST_THREAD_AREA (64, sizeof (struct pthread))
+  CONST_THREAD_AREA (64, TLS_PRE_TCB_SIZE)
 
 /* Access to data in the thread descriptor is easy.  */
 # define THREAD_GETMEM(descr, member) \
diff --git a/sysdeps/aarch64/tcb-version.c b/sysdeps/aarch64/tcb-version.c
new file mode 100644
index 0000000..c94e5d3
--- /dev/null
+++ b/sysdeps/aarch64/tcb-version.c
@@ -0,0 +1,23 @@
+/* TCB field abi advertise symbols.
+   Copyright (C) 2017 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/>.  */
+
+#include <libc-internal.h>
+
+/* Symbol used to version control the private GLIBC TCB split-stack
+   field.  */
+long int attribute_relro __libc_tcb_private_ss;
diff --git a/sysdeps/unix/sysv/linux/aarch64/ld.abilist b/sysdeps/unix/sysv/linux/aarch64/ld.abilist
index ec7f617..645d02d 100644
--- a/sysdeps/unix/sysv/linux/aarch64/ld.abilist
+++ b/sysdeps/unix/sysv/linux/aarch64/ld.abilist
@@ -8,3 +8,5 @@ GLIBC_2.17 calloc F
 GLIBC_2.17 free F
 GLIBC_2.17 malloc F
 GLIBC_2.17 realloc F
+GLIBC_2.26 GLIBC_2.26 A
+GLIBC_2.26 __libc_tcb_private_ss D 0x8
diff --git a/sysdeps/unix/sysv/linux/aarch64/sysdep-cancel.h b/sysdeps/unix/sysv/linux/aarch64/sysdep-cancel.h
index 4be2259..e4ac2ba 100644
--- a/sysdeps/unix/sysv/linux/aarch64/sysdep-cancel.h
+++ b/sysdeps/unix/sysv/linux/aarch64/sysdep-cancel.h
@@ -114,7 +114,7 @@ extern int __local_multiple_threads attribute_hidden;
 #  else
 #   define SINGLE_THREAD_P(R)						\
 	mrs     x##R, tpidr_el0;					\
-	sub	x##R, x##R, PTHREAD_SIZEOF;				\
+	sub	x##R, x##R, PTHREAD_PRE_TCB_SIZE;			\
 	ldr	w##R, [x##R, PTHREAD_MULTIPLE_THREADS_OFFSET]
 #  endif
 # endif
-- 
2.7.4