aarch64: Add split-stack TCB field
Commit Message
On 13/02/2018 14:56, Szabolcs Nagy wrote:
> On 07/02/18 17:58, Adhemerval Zanella wrote:
>> 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 before 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 the existence
>
> __libc_tcb_private_ss
Fixed locally.
>
>> 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.
>
> i don't see where PTHREAD_PRE_TCB_SIZE is used
> (or PTHREAD_SIZEOF)
Indeed, it is an artefact from previous version. I removed it in the patch below.
>> diff --git a/sysdeps/aarch64/nptl/tls.h b/sysdeps/aarch64/nptl/tls.h
>> index ac39c24..2d88310 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-pointer-arith.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))
>>
>
> it looks ok, but a bit ugly, i don't see a clean way
> to express the requirements in c.
>
> if i understand correctly the tls layout is
>
> struct pthread tcbprehead_t tcbhead_t static tls
> <--------------><-------------><----------><----------->
> ^
> TP
>
> where tcbprehead_t may overlap with paddings at the end
> of struct pthread.
>
> and we have to make sure offsets from TP to the members
> of tcbprehead_t don't change.
>
> i think there should be a comment about this layout and
> the alignment/offset requirements somewhere in tls.h
> (so next time it's easier to allocate such a tls slot)
I have added a comment about the layout and possible newer member
additions on tcbprehead_t.
--
* sysdeps/aarch64/Makefile [$(subdir) = elf] (sysdeps-dl-routines):
Add tcb-version.
* sysdeps/aarch64/Versions [ld] (GLIBC_2.28): 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_2.28): Add.
(__libc_tcb_private_ss): Likewise.
---
@@ -1,7 +1,7 @@
long-double-fcts = yes
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
@@ -3,3 +3,11 @@ libc {
_mcount;
}
}
+
+ld {
+ GLIBC_2.28 {
+ # Symbol used to version control the private GLIBC TCB split-stack
+ # field.
+ __libc_tcb_private_ss;
+ }
+}
@@ -26,6 +26,7 @@
# include <stddef.h>
# include <stdint.h>
# include <dl-dtv.h>
+# include <libc-pointer-arith.h>
#else /* __ASSEMBLER__ */
# include <tcb-offsets.h>
@@ -43,12 +44,32 @@
/* Get the thread descriptor definition. */
# include <nptl/descr.h>
+/* The resulting TLS layout is:
+
+ |----------------|--------------|-----------|------------|
+ | struct pthread | tcbprehead_t | tcbhead_t | static tls |
+ |----------------|--------------|-----------|------------|
+ \_ Thread pointer
+
+ And tcbprehead_t might overlap the padding at the end of the
+ struct pthread, otherwise extra space is allocated (check TLS_PRE_TCB_SIZE
+ definition).
+
+ Additional fields on tcbhead_t must keep member offset constant (so they
+ should be added at the beggining of the struct). */
+
typedef struct
{
dtv_t *dtv;
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 +79,14 @@ 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 +111,8 @@ 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 +120,12 @@ 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) \
new file mode 100644
@@ -0,0 +1,23 @@
+/* TCB field abi advertise symbols.
+ Copyright (C) 2017-2018 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/>. */
+
+#include <libc-internal.h>
+
+/* Symbol used to version control the private GLIBC TCB split-stack
+ field. */
+long int attribute_relro __libc_tcb_private_ss;
@@ -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_2.28 GLIBC_2.28 A
+GLIBC_2.28 __libc_tcb_private_ss D 0x8