[PATCHi v2] aarch64: Add split-stack TCB field

[Florian Weimer]

On 03/14/2017 02:17 AM, Carlos O'Donell wrote:
> On 02/14/2017 05:03 AM, Florian Weimer wrote:
>> On 02/13/2017 08:45 PM, Adhemerval Zanella wrote:
>>> +/* 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), sizeof (struct pthread))    \ +
>>> : 0))
>>
>> How does this preserve the alignment of struct pthread?
>>
>> It's also not clear to me how the “version control” aspect of
>> __tcb_private_ss is supposed to work.  If the intent is to prevent
>> loading of split-stack binaries with an older glibc, then a data
>> symbol would be a safer choice.
>
> Why is a data symbol a safer choice?

No lazy binding and hence a more well-defined failure mode.

Thanks,
Florian