[RFC,v4] Add rseq extensible ABI support

Message ID 20231201230138.19848-1-mjeanson@efficios.com
State Superseded
Headers
Series [RFC,v4] Add rseq extensible ABI support |

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Commit Message

Michael Jeanson Dec. 1, 2023, 11:01 p.m. UTC
  Introduced in Linux v6.3 the rseq extensible ABI [1] will allow adding
rseq features past the initial 32 bytes of the original ABI.

While the rseq features in the latest kernel still fit within the
original ABI size, there are currently only 4 bytes left. It would thus
be a good time to add support for the extensible ABI so that when new
features are added, they are immediately available to GNU libc users.

This is a first draft of a possible implementation to gather some
feedback.

We use the ELF auxiliary vectors to query the kernel for the size and
alignment of the rseq area, if this fails we default to the original
fixed size and alignment of '32' which the kernel will accept as a
compatibility mode with the original ABI.

This makes the size of the rseq area variable and thus requires to
relocate it out of 'struct pthread'. We chose to move it after (in block
allocation order) the last TLS block since it required a fairly small
modification to the TLS block allocator and did not interfere with the
main executable TLS block which must always be first.

[1] https://lore.kernel.org/all/20221122203932.231377-4-mathieu.desnoyers@efficios.com/

Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Co-Authored-By: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-By: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Carlos O'Donell <carlos@redhat.com>
---
Changes since RFC v1:
- Insert the rseq area after the last TLS block
- Add proper support for TLS_TCB_AT_TP variant
Changes since RFC v2:
- Set __rseq_size even when the registration fails
- Adjust rseq tests to the new ABI
- Added support for statically linked executables
Changes since RFC v3:
- Fix RSEQ_SETMEM for rseq disabled
- Replace sys/auxv.h usage with dl-parse_auxv.h
- Fix offset for TLS_TCB_AT_TP with statically linked executables
- Zero the rseq area before registration
---
 csu/libc-tls.c                             | 42 +++++++++++++++-
 elf/dl-tls.c                               | 55 +++++++++++++++++++++
 elf/rtld_static_init.c                     | 12 +++++
 nptl/descr.h                               | 20 ++------
 nptl/pthread_create.c                      |  2 +-
 sysdeps/generic/ldsodefs.h                 | 12 +++++
 sysdeps/i386/nptl/tcb-access.h             | 56 ++++++++++++++++++++++
 sysdeps/nptl/dl-tls_init_tp.c              | 19 ++++----
 sysdeps/nptl/tcb-access.h                  |  5 ++
 sysdeps/unix/sysv/linux/dl-parse_auxv.h    |  3 ++
 sysdeps/unix/sysv/linux/rseq-internal.h    | 29 +++++++++--
 sysdeps/unix/sysv/linux/sched_getcpu.c     |  3 +-
 sysdeps/unix/sysv/linux/tst-rseq-disable.c | 20 ++++----
 sysdeps/unix/sysv/linux/tst-rseq.c         | 18 +++++--
 sysdeps/unix/sysv/linux/tst-rseq.h         |  5 +-
 sysdeps/x86_64/nptl/tcb-access.h           | 56 ++++++++++++++++++++++
 16 files changed, 310 insertions(+), 47 deletions(-)
  

Comments

Mathieu Desnoyers Dec. 4, 2023, 2:42 p.m. UTC | #1
On 2023-12-01 18:01, Michael Jeanson wrote:
[...]
> 
> diff --git a/csu/libc-tls.c b/csu/libc-tls.c
> index cdf6442c02..6c96284b0c 100644
> --- a/csu/libc-tls.c
> +++ b/csu/libc-tls.c
> @@ -62,6 +62,18 @@ size_t _dl_tls_static_surplus;
>      dynamic TLS access (e.g. with TLSDESC).  */
>   size_t _dl_tls_static_optional;
>   
> +/* Size of the features present in the rseq area.  */
> +size_t _dl_tls_rseq_feature_size;
> +
> +/* Alignment requirement of the rseq area.  */
> +size_t _dl_tls_rseq_align;
> +
> +/* Size of the rseq area in the static TLS block.  */
> +size_t _dl_tls_rseq_size;
> +
> +/* Offset of the rseq area from the thread pointer.  */
> +ptrdiff_t _dl_tls_rseq_offset;
> +
>   /* Generation counter for the dtv.  */
>   size_t _dl_tls_generation;
>   
> @@ -135,6 +147,21 @@ __libc_setup_tls (void)
>     /* Calculate the size of the static TLS surplus, with 0 auditors.  */
>     _dl_tls_static_surplus_init (0);
>   
> +  /* Get the rseq auxiliary vectors, 0 is returned when not implemented
> +     and we then default to the rseq ABI minimums.  */
> +  size_t rseq_size = MAX (GLRO(dl_tls_rseq_feature_size), 32);
> +  size_t rseq_align = MAX (GLRO(dl_tls_rseq_align), 32);
> +
> +  /* Make sure the rseq area size is a multiple of the requested
> +     aligment. */
> +  rseq_size = roundup (rseq_size, rseq_align);
> +
> +  /* Increase the max_align if necessary.  */
> +  max_align = MAX (max_align, rseq_align);
> +
> + /* Record the rseq_area block size.  */
> +  GLRO (dl_tls_rseq_size) = rseq_size;
> +
>     /* We have to set up the TCB block which also (possibly) contains
>        'errno'.  Therefore we avoid 'malloc' which might touch 'errno'.
>        Instead we use 'sbrk' which would only uses 'errno' if it fails.
> @@ -144,13 +171,13 @@ __libc_setup_tls (void)
>     /* Align the TCB offset to the maximum alignment, as
>        _dl_allocate_tls_storage (in elf/dl-tls.c) does using __libc_memalign
>        and dl_tls_static_align.  */
> -  tcb_offset = roundup (memsz + GLRO(dl_tls_static_surplus), max_align);
> +  tcb_offset = roundup (memsz + rseq_size + GLRO(dl_tls_static_surplus), max_align);

If memsz alignment is smaller than rseq_align, I think we are missing padding here.
I think we got it right in the dynamic loader case, but the static linking case
seems wrong.

You could try to test it with a modified implementation which fakes that getauxval
returns a huge alignment (e.g. 256MB) and see what breaks.

>     tlsblock = _dl_early_allocate (tcb_offset + TLS_INIT_TCB_SIZE + max_align);
>     if (tlsblock == NULL)
>       _startup_fatal_tls_error ();
>   #elif TLS_DTV_AT_TP
>     tcb_offset = roundup (TLS_INIT_TCB_SIZE, align ?: 1);
> -  tlsblock = _dl_early_allocate (tcb_offset + memsz + max_align
> +  tlsblock = _dl_early_allocate (tcb_offset + memsz + rseq_size + max_align

I think this also does not take into account padding needed between memsz
and rseq_size if memsz has a smaller alignment than rseq.

>   				 + TLS_PRE_TCB_SIZE
>   				 + GLRO(dl_tls_static_surplus));
>     if (tlsblock == NULL)
> @@ -175,9 +202,17 @@ __libc_setup_tls (void)
>     _dl_static_dtv[2].pointer.val = ((char *) tlsblock + tcb_offset
>   			       - roundup (memsz, align ?: 1));
>     main_map->l_tls_offset = roundup (memsz, align ?: 1);
> +
> + /* Record the rseq_area offset. The offset is negative with TLS_TCB_AT_TP
> +    because the TLS blocks are located before the thread pointer.  */
> +  GLRO (dl_tls_rseq_offset) = - roundup (main_map->l_tls_offset + rseq_size, rseq_align);

Not sure if padding after memsz is taken into account here.

>   #elif TLS_DTV_AT_TP
>     _dl_static_dtv[2].pointer.val = (char *) tlsblock + tcb_offset;
>     main_map->l_tls_offset = tcb_offset;
> +
> + /* Record the rseq_area offset. The offset is positive with TLS_DTV_AT_TP
> +    because the TLS blocks are located after the thread pointer.  */
> +  GLRO (dl_tls_rseq_offset) = roundup (tcb_offset + memsz, rseq_align);

Likewise.

>   #else
>   # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
>   #endif
> @@ -215,5 +250,8 @@ __libc_setup_tls (void)
>     memsz += tcb_offset;
>   #endif
>   
> +  /* Add rseq area to the used size.  */
> +  memsz = roundup (memsz + rseq_size, rseq_align);

Same.

> +
>     init_static_tls (memsz, MAX (TCB_ALIGNMENT, max_align));
>   }
> diff --git a/elf/dl-tls.c b/elf/dl-tls.c
> index 70446e71a8..6e6a8f4e13 100644
> --- a/elf/dl-tls.c
> +++ b/elf/dl-tls.c
> @@ -75,6 +75,12 @@
>   /* Default for dl_tls_static_optional.  */
>   #define OPTIONAL_TLS 512
>   
> +/* Minimum size of the rseq area.  */
> +#define TLS_DL_RSEQ_MIN_SIZE 32
> +
> +/* Minimum size of the rseq area alignment.  */
> +#define TLS_DL_RSEQ_MIN_ALIGN 32
> +

We should move those define in a header common between elf-dl-tls.c and
csu/libc-tls.c, as those "32" values are hardcoded in the latter.

Thanks,

Mathieu
  
Michael Jeanson Dec. 5, 2023, 3:56 p.m. UTC | #2
On 2023-12-04 09:42, Mathieu Desnoyers wrote:
> On 2023-12-01 18:01, Michael Jeanson wrote:
> [...]
>>
>> diff --git a/csu/libc-tls.c b/csu/libc-tls.c
>> index cdf6442c02..6c96284b0c 100644
>> --- a/csu/libc-tls.c
>> +++ b/csu/libc-tls.c
>> @@ -62,6 +62,18 @@ size_t _dl_tls_static_surplus;
>>      dynamic TLS access (e.g. with TLSDESC).  */
>>   size_t _dl_tls_static_optional;
>> +/* Size of the features present in the rseq area.  */
>> +size_t _dl_tls_rseq_feature_size;
>> +
>> +/* Alignment requirement of the rseq area.  */
>> +size_t _dl_tls_rseq_align;
>> +
>> +/* Size of the rseq area in the static TLS block.  */
>> +size_t _dl_tls_rseq_size;
>> +
>> +/* Offset of the rseq area from the thread pointer.  */
>> +ptrdiff_t _dl_tls_rseq_offset;
>> +
>>   /* Generation counter for the dtv.  */
>>   size_t _dl_tls_generation;
>> @@ -135,6 +147,21 @@ __libc_setup_tls (void)
>>     /* Calculate the size of the static TLS surplus, with 0 auditors.  */
>>     _dl_tls_static_surplus_init (0);
>> +  /* Get the rseq auxiliary vectors, 0 is returned when not implemented
>> +     and we then default to the rseq ABI minimums.  */
>> +  size_t rseq_size = MAX (GLRO(dl_tls_rseq_feature_size), 32);
>> +  size_t rseq_align = MAX (GLRO(dl_tls_rseq_align), 32);
>> +
>> +  /* Make sure the rseq area size is a multiple of the requested
>> +     aligment. */
>> +  rseq_size = roundup (rseq_size, rseq_align);
>> +
>> +  /* Increase the max_align if necessary.  */
>> +  max_align = MAX (max_align, rseq_align);
>> +
>> + /* Record the rseq_area block size.  */
>> +  GLRO (dl_tls_rseq_size) = rseq_size;
>> +
>>     /* We have to set up the TCB block which also (possibly) contains
>>        'errno'.  Therefore we avoid 'malloc' which might touch 'errno'.
>>        Instead we use 'sbrk' which would only uses 'errno' if it fails.
>> @@ -144,13 +171,13 @@ __libc_setup_tls (void)
>>     /* Align the TCB offset to the maximum alignment, as
>>        _dl_allocate_tls_storage (in elf/dl-tls.c) does using __libc_memalign
>>        and dl_tls_static_align.  */
>> -  tcb_offset = roundup (memsz + GLRO(dl_tls_static_surplus), max_align);
>> +  tcb_offset = roundup (memsz + rseq_size + GLRO(dl_tls_static_surplus), 
>> max_align);
> 
> If memsz alignment is smaller than rseq_align, I think we are missing padding 
> here.
> I think we got it right in the dynamic loader case, but the static linking case
> seems wrong.

Indeed, I'll address this in the next version.

> You could try to test it with a modified implementation which fakes that 
> getauxval
> returns a huge alignment (e.g. 256MB) and see what breaks.
> 
>>     tlsblock = _dl_early_allocate (tcb_offset + TLS_INIT_TCB_SIZE + max_align);
>>     if (tlsblock == NULL)
>>       _startup_fatal_tls_error ();
>>   #elif TLS_DTV_AT_TP
>>     tcb_offset = roundup (TLS_INIT_TCB_SIZE, align ?: 1);
>> -  tlsblock = _dl_early_allocate (tcb_offset + memsz + max_align
>> +  tlsblock = _dl_early_allocate (tcb_offset + memsz + rseq_size + max_align
> 
> I think this also does not take into account padding needed between memsz
> and rseq_size if memsz has a smaller alignment than rseq.
> 
>>                    + TLS_PRE_TCB_SIZE
>>                    + GLRO(dl_tls_static_surplus));
>>     if (tlsblock == NULL)
>> @@ -175,9 +202,17 @@ __libc_setup_tls (void)
>>     _dl_static_dtv[2].pointer.val = ((char *) tlsblock + tcb_offset
>>                      - roundup (memsz, align ?: 1));
>>     main_map->l_tls_offset = roundup (memsz, align ?: 1);
>> +
>> + /* Record the rseq_area offset. The offset is negative with TLS_TCB_AT_TP
>> +    because the TLS blocks are located before the thread pointer.  */
>> +  GLRO (dl_tls_rseq_offset) = - roundup (main_map->l_tls_offset + 
>> rseq_size, rseq_align);
> 
> Not sure if padding after memsz is taken into account here.
> 
>>   #elif TLS_DTV_AT_TP
>>     _dl_static_dtv[2].pointer.val = (char *) tlsblock + tcb_offset;
>>     main_map->l_tls_offset = tcb_offset;
>> +
>> + /* Record the rseq_area offset. The offset is positive with TLS_DTV_AT_TP
>> +    because the TLS blocks are located after the thread pointer.  */
>> +  GLRO (dl_tls_rseq_offset) = roundup (tcb_offset + memsz, rseq_align);
> 
> Likewise.
> 
>>   #else
>>   # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
>>   #endif
>> @@ -215,5 +250,8 @@ __libc_setup_tls (void)
>>     memsz += tcb_offset;
>>   #endif
>> +  /* Add rseq area to the used size.  */
>> +  memsz = roundup (memsz + rseq_size, rseq_align);
> 
> Same.
> 
>> +
>>     init_static_tls (memsz, MAX (TCB_ALIGNMENT, max_align));
>>   }
>> diff --git a/elf/dl-tls.c b/elf/dl-tls.c
>> index 70446e71a8..6e6a8f4e13 100644
>> --- a/elf/dl-tls.c
>> +++ b/elf/dl-tls.c
>> @@ -75,6 +75,12 @@
>>   /* Default for dl_tls_static_optional.  */
>>   #define OPTIONAL_TLS 512
>> +/* Minimum size of the rseq area.  */
>> +#define TLS_DL_RSEQ_MIN_SIZE 32
>> +
>> +/* Minimum size of the rseq area alignment.  */
>> +#define TLS_DL_RSEQ_MIN_ALIGN 32
>> +
> 
> We should move those define in a header common between elf-dl-tls.c and
> csu/libc-tls.c, as those "32" values are hardcoded in the latter.

Ack.

> 
> Thanks,
> 
> Mathieu
>
  

Patch

diff --git a/csu/libc-tls.c b/csu/libc-tls.c
index cdf6442c02..6c96284b0c 100644
--- a/csu/libc-tls.c
+++ b/csu/libc-tls.c
@@ -62,6 +62,18 @@  size_t _dl_tls_static_surplus;
    dynamic TLS access (e.g. with TLSDESC).  */
 size_t _dl_tls_static_optional;
 
+/* Size of the features present in the rseq area.  */
+size_t _dl_tls_rseq_feature_size;
+
+/* Alignment requirement of the rseq area.  */
+size_t _dl_tls_rseq_align;
+
+/* Size of the rseq area in the static TLS block.  */
+size_t _dl_tls_rseq_size;
+
+/* Offset of the rseq area from the thread pointer.  */
+ptrdiff_t _dl_tls_rseq_offset;
+
 /* Generation counter for the dtv.  */
 size_t _dl_tls_generation;
 
@@ -135,6 +147,21 @@  __libc_setup_tls (void)
   /* Calculate the size of the static TLS surplus, with 0 auditors.  */
   _dl_tls_static_surplus_init (0);
 
+  /* Get the rseq auxiliary vectors, 0 is returned when not implemented
+     and we then default to the rseq ABI minimums.  */
+  size_t rseq_size = MAX (GLRO(dl_tls_rseq_feature_size), 32);
+  size_t rseq_align = MAX (GLRO(dl_tls_rseq_align), 32);
+
+  /* Make sure the rseq area size is a multiple of the requested
+     aligment. */
+  rseq_size = roundup (rseq_size, rseq_align);
+
+  /* Increase the max_align if necessary.  */
+  max_align = MAX (max_align, rseq_align);
+
+ /* Record the rseq_area block size.  */
+  GLRO (dl_tls_rseq_size) = rseq_size;
+
   /* We have to set up the TCB block which also (possibly) contains
      'errno'.  Therefore we avoid 'malloc' which might touch 'errno'.
      Instead we use 'sbrk' which would only uses 'errno' if it fails.
@@ -144,13 +171,13 @@  __libc_setup_tls (void)
   /* Align the TCB offset to the maximum alignment, as
      _dl_allocate_tls_storage (in elf/dl-tls.c) does using __libc_memalign
      and dl_tls_static_align.  */
-  tcb_offset = roundup (memsz + GLRO(dl_tls_static_surplus), max_align);
+  tcb_offset = roundup (memsz + rseq_size + GLRO(dl_tls_static_surplus), max_align);
   tlsblock = _dl_early_allocate (tcb_offset + TLS_INIT_TCB_SIZE + max_align);
   if (tlsblock == NULL)
     _startup_fatal_tls_error ();
 #elif TLS_DTV_AT_TP
   tcb_offset = roundup (TLS_INIT_TCB_SIZE, align ?: 1);
-  tlsblock = _dl_early_allocate (tcb_offset + memsz + max_align
+  tlsblock = _dl_early_allocate (tcb_offset + memsz + rseq_size + max_align
 				 + TLS_PRE_TCB_SIZE
 				 + GLRO(dl_tls_static_surplus));
   if (tlsblock == NULL)
@@ -175,9 +202,17 @@  __libc_setup_tls (void)
   _dl_static_dtv[2].pointer.val = ((char *) tlsblock + tcb_offset
 			       - roundup (memsz, align ?: 1));
   main_map->l_tls_offset = roundup (memsz, align ?: 1);
+
+ /* Record the rseq_area offset. The offset is negative with TLS_TCB_AT_TP
+    because the TLS blocks are located before the thread pointer.  */
+  GLRO (dl_tls_rseq_offset) = - roundup (main_map->l_tls_offset + rseq_size, rseq_align);
 #elif TLS_DTV_AT_TP
   _dl_static_dtv[2].pointer.val = (char *) tlsblock + tcb_offset;
   main_map->l_tls_offset = tcb_offset;
+
+ /* Record the rseq_area offset. The offset is positive with TLS_DTV_AT_TP
+    because the TLS blocks are located after the thread pointer.  */
+  GLRO (dl_tls_rseq_offset) = roundup (tcb_offset + memsz, rseq_align);
 #else
 # error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
 #endif
@@ -215,5 +250,8 @@  __libc_setup_tls (void)
   memsz += tcb_offset;
 #endif
 
+  /* Add rseq area to the used size.  */
+  memsz = roundup (memsz + rseq_size, rseq_align);
+
   init_static_tls (memsz, MAX (TCB_ALIGNMENT, max_align));
 }
diff --git a/elf/dl-tls.c b/elf/dl-tls.c
index 70446e71a8..6e6a8f4e13 100644
--- a/elf/dl-tls.c
+++ b/elf/dl-tls.c
@@ -75,6 +75,12 @@ 
 /* Default for dl_tls_static_optional.  */
 #define OPTIONAL_TLS 512
 
+/* Minimum size of the rseq area.  */
+#define TLS_DL_RSEQ_MIN_SIZE 32
+
+/* Minimum size of the rseq area alignment.  */
+#define TLS_DL_RSEQ_MIN_ALIGN 32
+
 /* Compute the static TLS surplus based on the namespace count and the
    TLS space that can be used for optimizations.  */
 static inline int
@@ -298,6 +304,29 @@  _dl_determine_tlsoffset (void)
       slotinfo[cnt].map->l_tls_offset = off;
     }
 
+  /* Insert the rseq area block after the last TLS block.  */
+
+  /* Get the rseq auxiliary vectors, 0 is returned when not implemented
+     and we then default to the rseq ABI minimums.  */
+  size_t rseq_size = MAX (GLRO (dl_tls_rseq_feature_size), TLS_DL_RSEQ_MIN_SIZE);
+  size_t rseq_align = MAX (GLRO (dl_tls_rseq_align), TLS_DL_RSEQ_MIN_ALIGN);
+
+  /* Make sure the rseq area size is a multiple of the requested
+     aligment. */
+  rseq_size = roundup (rseq_size, rseq_align);
+
+  /* Add the rseq area block to the global offset.  */
+  offset = roundup (offset, rseq_align) + rseq_size;
+
+  /* Increase the max_align if necessary.  */
+  max_align = MAX (max_align, rseq_align);
+
+ /* Record the rseq_area block size and offset. The offset is negative
+    with TLS_TCB_AT_TP because the TLS blocks are located before the
+    thread pointer.  */
+  GLRO (dl_tls_rseq_offset) = -offset;
+  GLRO (dl_tls_rseq_size) = rseq_size;
+
   GL(dl_tls_static_used) = offset;
   GLRO (dl_tls_static_size) = (roundup (offset + GLRO(dl_tls_static_surplus),
 					max_align)
@@ -343,6 +372,32 @@  _dl_determine_tlsoffset (void)
       offset = off + slotinfo[cnt].map->l_tls_blocksize - firstbyte;
     }
 
+  /* Insert the rseq area block after the last TLS block.  */
+
+  /* Get the rseq auxiliary vectors, 0 is returned when not implemented
+     and we then default to the rseq ABI minimums.  */
+  size_t rseq_size = MAX (GLRO (dl_tls_rseq_feature_size), TLS_DL_RSEQ_MIN_SIZE);
+  size_t rseq_align = MAX (GLRO (dl_tls_rseq_align), TLS_DL_RSEQ_MIN_ALIGN);
+
+  /* Make sure the rseq area size is a multiple of the requested
+     aligment. */
+  rseq_size = roundup (rseq_size, rseq_align);
+
+  /* Align the global offset to the beginning of the rseq area.  */
+  offset = roundup (offset, rseq_align);
+
+  /* Record the rseq_area block size and offset. The offset is positive
+     with TLS_DTV_AT_TP because the TLS blocks are located after the
+     thread pointer.  */
+  GLRO (dl_tls_rseq_size) = rseq_size;
+  GLRO (dl_tls_rseq_offset) = offset;
+
+  /* Add the rseq area block to the global offset.  */
+  offset += rseq_size;
+
+  /* Increase the max_align if necessary.  */
+  max_align = MAX (max_align, rseq_align);
+
   GL(dl_tls_static_used) = offset;
   GLRO (dl_tls_static_size) = roundup (offset + GLRO(dl_tls_static_surplus),
 				       TCB_ALIGNMENT);
diff --git a/elf/rtld_static_init.c b/elf/rtld_static_init.c
index aec8cc056b..5d7ee37d67 100644
--- a/elf/rtld_static_init.c
+++ b/elf/rtld_static_init.c
@@ -78,6 +78,18 @@  __rtld_static_init (struct link_map *map)
   extern __typeof (dl->_dl_tls_static_size) _dl_tls_static_size
     attribute_hidden;
   dl->_dl_tls_static_size = _dl_tls_static_size;
+  extern __typeof (dl->_dl_tls_rseq_feature_size) _dl_tls_rseq_feature_size
+    attribute_hidden;
+  dl->_dl_tls_rseq_feature_size = _dl_tls_rseq_feature_size;
+  extern __typeof (dl->_dl_tls_rseq_align) _dl_tls_rseq_align
+    attribute_hidden;
+  dl->_dl_tls_rseq_align = _dl_tls_rseq_align;
+  extern __typeof (dl->_dl_tls_rseq_size) _dl_tls_rseq_size
+    attribute_hidden;
+  dl->_dl_tls_rseq_size = _dl_tls_rseq_size;
+  extern __typeof (dl->_dl_tls_rseq_offset) _dl_tls_rseq_offset
+    attribute_hidden;
+  dl->_dl_tls_rseq_offset = _dl_tls_rseq_offset;
   dl->_dl_find_object = _dl_find_object;
 
   __rtld_static_init_arch (map, dl);
diff --git a/nptl/descr.h b/nptl/descr.h
index 0171576c23..fadba1f619 100644
--- a/nptl/descr.h
+++ b/nptl/descr.h
@@ -404,25 +404,11 @@  struct pthread
   /* Used on strsignal.  */
   struct tls_internal_t tls_state;
 
-  /* rseq area registered with the kernel.  Use a custom definition
-     here to isolate from kernel struct rseq changes.  The
-     implementation of sched_getcpu needs acccess to the cpu_id field;
-     the other fields are unused and not included here.  */
-  union
-  {
-    struct
-    {
-      uint32_t cpu_id_start;
-      uint32_t cpu_id;
-    };
-    char pad[32];		/* Original rseq area size.  */
-  } rseq_area __attribute__ ((aligned (32)));
-
   /* Amount of end padding, if any, in this structure.
-     This definition relies on rseq_area being last.  */
+     This definition relies on tls_state being last.  */
 #define PTHREAD_STRUCT_END_PADDING \
-  (sizeof (struct pthread) - offsetof (struct pthread, rseq_area) \
-   + sizeof ((struct pthread) {}.rseq_area))
+  (sizeof (struct pthread) - offsetof (struct pthread, tls_state) \
+   + sizeof ((struct pthread) {}.tls_state))
 } __attribute ((aligned (TCB_ALIGNMENT)));
 
 static inline bool
diff --git a/nptl/pthread_create.c b/nptl/pthread_create.c
index 63cb684f04..4ee0f24741 100644
--- a/nptl/pthread_create.c
+++ b/nptl/pthread_create.c
@@ -691,7 +691,7 @@  __pthread_create_2_1 (pthread_t *newthread, const pthread_attr_t *attr,
 
   /* Inherit rseq registration state.  Without seccomp filters, rseq
      registration will either always fail or always succeed.  */
-  if ((int) THREAD_GETMEM_VOLATILE (self, rseq_area.cpu_id) >= 0)
+  if ((int) RSEQ_GETMEM_VOLATILE (rseq_get_area(), cpu_id) >= 0)
     pd->flags |= ATTR_FLAG_DO_RSEQ;
 
   /* Initialize the field for the ID of the thread which is waiting
diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
index 9b50ddd09f..14ed361d94 100644
--- a/sysdeps/generic/ldsodefs.h
+++ b/sysdeps/generic/ldsodefs.h
@@ -610,6 +610,18 @@  struct rtld_global_ro
      See comments in elf/dl-tls.c where it is initialized.  */
   EXTERN size_t _dl_tls_static_surplus;
 
+  /* Size of the features present in the rseq area.  */
+  EXTERN size_t _dl_tls_rseq_feature_size;
+
+  /* Alignment requirement of the rseq area.  */
+  EXTERN size_t _dl_tls_rseq_align;
+
+  /* Size of the rseq area in the static TLS block.  */
+  EXTERN size_t _dl_tls_rseq_size;
+
+  /* Offset of the rseq area from the thread pointer.  */
+  EXTERN ptrdiff_t _dl_tls_rseq_offset;
+
   /* Name of the shared object to be profiled (if any).  */
   EXTERN const char *_dl_profile;
   /* Filename of the output file.  */
diff --git a/sysdeps/i386/nptl/tcb-access.h b/sysdeps/i386/nptl/tcb-access.h
index 28f0a5625f..e73802f5f5 100644
--- a/sysdeps/i386/nptl/tcb-access.h
+++ b/sysdeps/i386/nptl/tcb-access.h
@@ -123,3 +123,59 @@ 
 			 "i" (offsetof (struct pthread, member)),	      \
 			 "r" (idx));					      \
        }})
+
+
+/* Read member of the RSEQ area directly.  */
+#define RSEQ_GETMEM_VOLATILE(descr, member) \
+  ({ __typeof (descr->member) __value;					      \
+     ptrdiff_t _rseq_offset = GLRO (dl_tls_rseq_offset);		      \
+     _Static_assert (sizeof (__value) == 1				      \
+		     || sizeof (__value) == 4				      \
+		     || sizeof (__value) == 8,				      \
+		     "size of per-thread data");			      \
+     if (sizeof (__value) == 1)						      \
+       asm volatile ("movb %%gs:%P2(%3),%b0"				      \
+		     : "=q" (__value)					      \
+		     : "0" (0), "i" (offsetof (struct rseq_area, member)),   \
+		     "r" (_rseq_offset));					      \
+     else if (sizeof (__value) == 4)					      \
+       asm volatile ("movl %%gs:%P1(%2),%0"				      \
+		     : "=r" (__value)					      \
+		     : "i" (offsetof (struct rseq_area, member)),	      \
+		       "r" (_rseq_offset));					      \
+     else /* 8 */							      \
+       {								      \
+	 asm volatile  ("movl %%gs:%P1(%2),%%eax\n\t"			      \
+			"movl %%gs:4+%P1(%2),%%edx"			      \
+			: "=&A" (__value)				      \
+			: "i" (offsetof (struct rseq_area, member)),	      \
+			  "r" (_rseq_offset));				      \
+       }								      \
+     __value; })
+
+/* Set member of the RSEQ area directly.  */
+#define RSEQ_SETMEM(descr, member, value) \
+  ({									      \
+     ptrdiff_t _rseq_offset = GLRO (dl_tls_rseq_offset);		      \
+     _Static_assert (sizeof (descr->member) == 1			      \
+		     || sizeof (descr->member) == 4			      \
+		     || sizeof (descr->member) == 8,			      \
+		     "size of per-thread data");			      \
+     if (sizeof (descr->member) == 1)					      \
+       asm volatile ("movb %b0,%%gs:%P1(%2)" :				      \
+		     : "iq" (value),					      \
+		       "i" (offsetof (struct rseq_area, member)),	      \
+		       "r" (_rseq_offset));					      \
+     else if (sizeof (descr->member) == 4)				      \
+       asm volatile ("movl %0,%%gs:%P1(%2)" :				      \
+		     : "ir" (value),					      \
+		       "i" (offsetof (struct rseq_area, member)),	      \
+		       "r" (_rseq_offset));					      \
+     else /* 8 */							      \
+       {								      \
+	 asm volatile ("movl %%eax,%%gs:%P1(%2)\n\t"			      \
+		       "movl %%edx,%%gs:4+%P1(%2)" :			      \
+		       : "A" ((uint64_t) cast_to_integer (value)),	      \
+			 "i" (offsetof (struct rseq_area, member)),	      \
+			 "r" (_rseq_offset));				      \
+       }})
diff --git a/sysdeps/nptl/dl-tls_init_tp.c b/sysdeps/nptl/dl-tls_init_tp.c
index 2ed98c5a31..bc4549d240 100644
--- a/sysdeps/nptl/dl-tls_init_tp.c
+++ b/sysdeps/nptl/dl-tls_init_tp.c
@@ -103,13 +103,16 @@  __tls_init_tp (void)
   {
     bool do_rseq = true;
     do_rseq = TUNABLE_GET (rseq, int, NULL);
-    if (rseq_register_current_thread (pd, do_rseq))
-      {
-        /* We need a writable view of the variables.  They are in
-           .data.relro and are not yet write-protected.  */
-        extern unsigned int size __asm__ ("__rseq_size");
-        size = sizeof (pd->rseq_area);
-      }
+    rseq_register_current_thread (pd, do_rseq);
+
+    // FIXME: Even if the registration fails, we need to communicate the size
+    // of the allocated rseq area to an application that could attempt the
+    // registration itself.
+
+    /* We need a writable view of the variables.  They are in
+       .data.relro and are not yet write-protected.  */
+    extern unsigned int size __asm__ ("__rseq_size");
+    size = GLRO (dl_tls_rseq_size);
 
 #ifdef RSEQ_SIG
     /* This should be a compile-time constant, but the current
@@ -118,7 +121,7 @@  __tls_init_tp (void)
        if the rseq registration may have happened because RSEQ_SIG is
        defined.  */
     extern ptrdiff_t offset __asm__ ("__rseq_offset");
-    offset = (char *) &pd->rseq_area - (char *) __thread_pointer ();
+    offset = GLRO (dl_tls_rseq_offset);
 #endif
   }
 
diff --git a/sysdeps/nptl/tcb-access.h b/sysdeps/nptl/tcb-access.h
index d6dfd41391..7092428d38 100644
--- a/sysdeps/nptl/tcb-access.h
+++ b/sysdeps/nptl/tcb-access.h
@@ -30,3 +30,8 @@ 
   descr->member = (value)
 #define THREAD_SETMEM_NC(descr, member, idx, value) \
   descr->member[idx] = (value)
+
+#define RSEQ_GETMEM_VOLATILE(descr, member) \
+  THREAD_GETMEM_VOLATILE(descr, member)
+#define RSEQ_SETMEM(descr, member, value) \
+  THREAD_SETMEM(descr, member, value)
diff --git a/sysdeps/unix/sysv/linux/dl-parse_auxv.h b/sysdeps/unix/sysv/linux/dl-parse_auxv.h
index cf5e81bf2c..fa6e6db398 100644
--- a/sysdeps/unix/sysv/linux/dl-parse_auxv.h
+++ b/sysdeps/unix/sysv/linux/dl-parse_auxv.h
@@ -57,5 +57,8 @@  void _dl_parse_auxv (ElfW(auxv_t) *av, dl_parse_auxv_t auxv_values)
     GLRO(dl_sysinfo) = auxv_values[AT_SYSINFO];
 #endif
 
+  GLRO(dl_tls_rseq_feature_size) = auxv_values[AT_RSEQ_FEATURE_SIZE];
+  GLRO(dl_tls_rseq_align) = auxv_values[AT_RSEQ_ALIGN];
+
   DL_PLATFORM_AUXV
 }
diff --git a/sysdeps/unix/sysv/linux/rseq-internal.h b/sysdeps/unix/sysv/linux/rseq-internal.h
index 294880c04e..d372f95315 100644
--- a/sysdeps/unix/sysv/linux/rseq-internal.h
+++ b/sysdeps/unix/sysv/linux/rseq-internal.h
@@ -24,6 +24,24 @@ 
 #include <stdbool.h>
 #include <stdio.h>
 #include <sys/rseq.h>
+#include <thread_pointer.h>
+#include <ldsodefs.h>
+
+/* rseq area registered with the kernel.  Use a custom definition
+   here to isolate from kernel struct rseq changes.  The
+   implementation of sched_getcpu needs acccess to the cpu_id field;
+   the other fields are unused and not included here.  */
+struct rseq_area
+{
+  uint32_t cpu_id_start;
+  uint32_t cpu_id;
+};
+
+static inline struct rseq_area *
+rseq_get_area(void)
+{
+  return (struct rseq_area *) ((char *) __thread_pointer() + GLRO (dl_tls_rseq_offset));
+}
 
 #ifdef RSEQ_SIG
 static inline bool
@@ -31,20 +49,23 @@  rseq_register_current_thread (struct pthread *self, bool do_rseq)
 {
   if (do_rseq)
     {
-      int ret = INTERNAL_SYSCALL_CALL (rseq, &self->rseq_area,
-                                       sizeof (self->rseq_area),
+      /* The kernel expects 'rseq_area->rseq_cs == NULL' on registration, zero
+         the whole rseq area.  */
+      memset(rseq_get_area(), 0, GLRO (dl_tls_rseq_size));
+      int ret = INTERNAL_SYSCALL_CALL (rseq, rseq_get_area(),
+                                       GLRO (dl_tls_rseq_size),
                                        0, RSEQ_SIG);
       if (!INTERNAL_SYSCALL_ERROR_P (ret))
         return true;
     }
-  THREAD_SETMEM (self, rseq_area.cpu_id, RSEQ_CPU_ID_REGISTRATION_FAILED);
+  RSEQ_SETMEM (rseq_get_area(), cpu_id, RSEQ_CPU_ID_REGISTRATION_FAILED);
   return false;
 }
 #else /* RSEQ_SIG */
 static inline bool
 rseq_register_current_thread (struct pthread *self, bool do_rseq)
 {
-  THREAD_SETMEM (self, rseq_area.cpu_id, RSEQ_CPU_ID_REGISTRATION_FAILED);
+  RSEQ_SETMEM (rseq_get_area(), cpu_id, RSEQ_CPU_ID_REGISTRATION_FAILED);
   return false;
 }
 #endif /* RSEQ_SIG */
diff --git a/sysdeps/unix/sysv/linux/sched_getcpu.c b/sysdeps/unix/sysv/linux/sched_getcpu.c
index 4457d714bc..6109c68625 100644
--- a/sysdeps/unix/sysv/linux/sched_getcpu.c
+++ b/sysdeps/unix/sysv/linux/sched_getcpu.c
@@ -19,6 +19,7 @@ 
 #include <sched.h>
 #include <sysdep.h>
 #include <sysdep-vdso.h>
+#include <rseq-internal.h>
 
 static int
 vsyscall_sched_getcpu (void)
@@ -37,7 +38,7 @@  vsyscall_sched_getcpu (void)
 int
 sched_getcpu (void)
 {
-  int cpu_id = THREAD_GETMEM_VOLATILE (THREAD_SELF, rseq_area.cpu_id);
+  int cpu_id = RSEQ_GETMEM_VOLATILE (rseq_get_area(), cpu_id);
   return __glibc_likely (cpu_id >= 0) ? cpu_id : vsyscall_sched_getcpu ();
 }
 #else /* RSEQ_SIG */
diff --git a/sysdeps/unix/sysv/linux/tst-rseq-disable.c b/sysdeps/unix/sysv/linux/tst-rseq-disable.c
index cc7e94b3fe..a58d35ba02 100644
--- a/sysdeps/unix/sysv/linux/tst-rseq-disable.c
+++ b/sysdeps/unix/sysv/linux/tst-rseq-disable.c
@@ -23,6 +23,7 @@ 
 #include <sysdep.h>
 #include <thread_pointer.h>
 #include <sys/rseq.h>
+#include <sys/auxv.h>
 #include <unistd.h>
 
 #ifdef RSEQ_SIG
@@ -31,22 +32,23 @@ 
 static void
 check_rseq_disabled (void)
 {
-  struct pthread *pd = THREAD_SELF;
+  size_t rseq_size = MAX (getauxval (AT_RSEQ_FEATURE_SIZE), 32);
+  struct rseq *rseq_area = (struct rseq *) ((char *) __thread_pointer () + __rseq_offset);
 
   TEST_COMPARE (__rseq_flags, 0);
-  TEST_VERIFY ((char *) __thread_pointer () + __rseq_offset
-               == (char *) &pd->rseq_area);
-  TEST_COMPARE (__rseq_size, 0);
-  TEST_COMPARE ((int) pd->rseq_area.cpu_id, RSEQ_CPU_ID_REGISTRATION_FAILED);
+  //FIXME: unsure how to test this
+  //TEST_VERIFY ((char *) __thread_pointer () + __rseq_offset
+  //             == (char *) &pd->rseq_area);
+  TEST_COMPARE (__rseq_size, rseq_size);
+  TEST_COMPARE ((int) rseq_area->cpu_id, RSEQ_CPU_ID_REGISTRATION_FAILED);
 
-  int ret = syscall (__NR_rseq, &pd->rseq_area, sizeof (pd->rseq_area),
-                     0, RSEQ_SIG);
+  int ret = syscall (__NR_rseq, rseq_area, __rseq_size, 0, RSEQ_SIG);
   if (ret == 0)
     {
-      ret = syscall (__NR_rseq, &pd->rseq_area, sizeof (pd->rseq_area),
+      ret = syscall (__NR_rseq, rseq_area, __rseq_size,
                      RSEQ_FLAG_UNREGISTER, RSEQ_SIG);
       TEST_COMPARE (ret, 0);
-      pd->rseq_area.cpu_id = RSEQ_CPU_ID_REGISTRATION_FAILED;
+      rseq_area->cpu_id = RSEQ_CPU_ID_REGISTRATION_FAILED;
     }
   else
     {
diff --git a/sysdeps/unix/sysv/linux/tst-rseq.c b/sysdeps/unix/sysv/linux/tst-rseq.c
index 16983503b1..ed62c0f64a 100644
--- a/sysdeps/unix/sysv/linux/tst-rseq.c
+++ b/sysdeps/unix/sysv/linux/tst-rseq.c
@@ -31,18 +31,28 @@ 
 # include <syscall.h>
 # include <thread_pointer.h>
 # include <tls.h>
+# include <sys/auxv.h>
 # include "tst-rseq.h"
 
 static void
 do_rseq_main_test (void)
 {
-  struct pthread *pd = THREAD_SELF;
+  size_t rseq_size = MAX (getauxval (AT_RSEQ_FEATURE_SIZE), 32);
 
   TEST_VERIFY_EXIT (rseq_thread_registered ());
   TEST_COMPARE (__rseq_flags, 0);
-  TEST_VERIFY ((char *) __thread_pointer () + __rseq_offset
-               == (char *) &pd->rseq_area);
-  TEST_COMPARE (__rseq_size, sizeof (pd->rseq_area));
+  TEST_COMPARE (__rseq_size, rseq_size);
+  /* rseq area minimum ABI size is 32 bytes. */
+  TEST_VERIFY (__rseq_size >= 32);
+#if TLS_TCB_AT_TP
+  /* rseq area block should come before the thread pointer and be at least 32 bytes. */
+  TEST_VERIFY (__rseq_offset <= 32);
+#elif TLS_DTV_AT_TP
+  /* rseq area block should come after the thread pointer. */
+  TEST_VERIFY (__rseq_offset >= 0);
+#else
+# error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
+#endif
 }
 
 static void
diff --git a/sysdeps/unix/sysv/linux/tst-rseq.h b/sysdeps/unix/sysv/linux/tst-rseq.h
index 95d12048df..dbfee88c07 100644
--- a/sysdeps/unix/sysv/linux/tst-rseq.h
+++ b/sysdeps/unix/sysv/linux/tst-rseq.h
@@ -23,11 +23,14 @@ 
 #include <syscall.h>
 #include <sys/rseq.h>
 #include <tls.h>
+#include <rseq-internal.h>
 
 static inline bool
 rseq_thread_registered (void)
 {
-  return THREAD_GETMEM_VOLATILE (THREAD_SELF, rseq_area.cpu_id) >= 0;
+  struct rseq_area *rseq = (struct rseq_area *) ((char *) __thread_pointer () + __rseq_offset);
+
+  return __atomic_load_n (&rseq->cpu_id, __ATOMIC_RELAXED) >= 0;
 }
 
 static inline int
diff --git a/sysdeps/x86_64/nptl/tcb-access.h b/sysdeps/x86_64/nptl/tcb-access.h
index 110b1be44d..3a943b2fba 100644
--- a/sysdeps/x86_64/nptl/tcb-access.h
+++ b/sysdeps/x86_64/nptl/tcb-access.h
@@ -130,3 +130,59 @@ 
 			 "i" (offsetof (struct pthread, member[0])),	      \
 			 "r" (idx));					      \
        }})
+
+/* Read member of the RSEQ area directly.  */
+# define RSEQ_GETMEM_VOLATILE(descr, member) \
+  ({ __typeof (descr->member) __value;					      \
+     ptrdiff_t _rseq_offset = GLRO (dl_tls_rseq_offset);		      \
+     _Static_assert (sizeof (__value) == 1				      \
+		     || sizeof (__value) == 4				      \
+		     || sizeof (__value) == 8,				      \
+		     "size of per-thread data");			      \
+     if (sizeof (__value) == 1)						      \
+       asm volatile ("movb %%fs:%P2(%q3),%b0"				      \
+		     : "=q" (__value)					      \
+		     : "0" (0), "i" (offsetof (struct rseq_area, member)),    \
+		       "r" (_rseq_offset));					      \
+     else if (sizeof (__value) == 4)					      \
+       asm volatile ("movl %%fs:%P1(%q2),%0"				      \
+		     : "=r" (__value)					      \
+		     : "i" (offsetof (struct rseq_area, member)),	      \
+		       "r" (_rseq_offset));					      \
+     else /* 8 */							      \
+       {								      \
+	 asm volatile ("movq %%fs:%P1(%q2),%q0"				      \
+		       : "=r" (__value)					      \
+		       : "i" (offsetof (struct rseq_area, member)),	      \
+			 "r" (_rseq_offset));				      \
+       }								      \
+     __value; })
+
+/* Set member of the RSEQ area directly.  */
+# define RSEQ_SETMEM(descr, member, value) \
+  ({									      \
+     ptrdiff_t _rseq_offset = GLRO (dl_tls_rseq_offset);		      \
+     _Static_assert (sizeof (descr->member) == 1			      \
+		     || sizeof (descr->member) == 4			      \
+		     || sizeof (descr->member) == 8,			      \
+		     "size of per-thread data");			      \
+     if (sizeof (descr->member) == 1)					      \
+       asm volatile ("movb %b0,%%fs:%P1(%q2)" :				      \
+		     : "iq" (value),					      \
+		       "i" (offsetof (struct rseq_area, member)),	      \
+		       "r" (_rseq_offset));					      \
+     else if (sizeof (descr->member) == 4)				      \
+       asm volatile ("movl %0,%%fs:%P1(%q2)" :				      \
+		     : IMM_MODE (value),				      \
+		       "i" (offsetof (struct rseq_area, member)),	      \
+		       "r" (_rseq_offset));					      \
+     else /* 8 */							      \
+       {								      \
+	 /* Since movq takes a signed 32-bit immediate or a register source   \
+	    operand, use "er" constraint for 32-bit signed integer constant   \
+	    or register.  */						      \
+	 asm volatile ("movq %q0,%%fs:%P1(%q2)" :			      \
+		       : "er" ((uint64_t) cast_to_integer (value)),	      \
+			 "i" (offsetof (struct rseq_area, member)),	      \
+			 "r" (_rseq_offset));				      \
+       }})