[PATCH] aarch64: Add split-stack TCB field
Szabolcs Nagy
szabolcs.nagy@arm.com
Tue Feb 13 19:40:00 GMT 2018
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
> of the split stack guard area.
>
> Checked on aarch64-linux-gnu.
>
> * sysdeps/aarch64/Makefile [$(subdir) = elf] (sysdeps-dl-routines):
> Add tcb-version.
> * sysdeps/aarch64/Versions [ld] (GLIBC_2.26): Add
> __libc_tcb_private_ss.
> * sysdeps/aarch64/nptl/tls.h (tcbprehead_t): New struct.
> (TLS_PRE_TCB_SIZE): Take tcbprehead_t in consideration.
> (TLS_DEFINE_INIT_TP): Likewise.
> (THREAD_SELF): Likewise.
> (DB_THREAD_SELF): Likewise.
> * sysdeps/aarch64/tcb-version.c: New file.
> * sysdeps/unix/sysv/linux/aarch64/ld.abilist (GLIBC_2.26): Add.
> (__libc_tcb_private_ss): Likewise.
> * sysdeps/aarch64/nptl/tcb-offsets.sym (PTHREAD_SIZEOF): Rename to
> PTHREAD_PRE_TCB_SIZE.
i don't see where PTHREAD_PRE_TCB_SIZE is used
(or PTHREAD_SIZEOF)
> ---
> ChangeLog | 17 +++++++++++++++++
> sysdeps/aarch64/Makefile | 2 +-
> sysdeps/aarch64/Versions | 8 ++++++++
> sysdeps/aarch64/nptl/tcb-offsets.sym | 2 +-
> sysdeps/aarch64/nptl/tls.h | 25 ++++++++++++++++++++-----
> sysdeps/aarch64/tcb-version.c | 23 +++++++++++++++++++++++
> sysdeps/unix/sysv/linux/aarch64/ld.abilist | 2 ++
> 7 files changed, 72 insertions(+), 7 deletions(-)
> create mode 100644 sysdeps/aarch64/tcb-version.c
>
> diff --git a/sysdeps/aarch64/Makefile b/sysdeps/aarch64/Makefile
> index 5f3e203..141442a 100644
> --- a/sysdeps/aarch64/Makefile
> +++ b/sysdeps/aarch64/Makefile
> @@ -1,7 +1,7 @@
> long-double-fcts = yes
>
> ifeq ($(subdir),elf)
> -sysdep-dl-routines += tlsdesc dl-tlsdesc
> +sysdep-dl-routines += tlsdesc dl-tlsdesc tcb-version
> gen-as-const-headers += dl-link.sym
> endif
>
> diff --git a/sysdeps/aarch64/Versions b/sysdeps/aarch64/Versions
> index e1aa44f..dcc395c 100644
> --- a/sysdeps/aarch64/Versions
> +++ b/sysdeps/aarch64/Versions
> @@ -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;
> + }
> +}
> 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 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)
> /* 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..aaddb24 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_2.28 GLIBC_2.28 A
> +GLIBC_2.28 __libc_tcb_private_ss D 0x8
>
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