Add AArch64 HWCAPs from Linux 5.0

[Szabolcs Nagy]

On 19/03/2019 14:34, Florian Weimer wrote:
> * Szabolcs Nagy:
> 
>>> diff --git a/sysdeps/unix/sysv/linux/aarch64/bits/hwcap.h
>>> b/sysdeps/unix/sysv/linux/aarch64/bits/hwcap.h
>>> index 9a395c597f..5f50623953 100644
>>> --- a/sysdeps/unix/sysv/linux/aarch64/bits/hwcap.h
>>> +++ b/sysdeps/unix/sysv/linux/aarch64/bits/hwcap.h
>>> @@ -51,3 +51,6 @@
>>>  #define HWCAP_ILRCPC		(1 << 26)
>>>  #define HWCAP_FLAGM		(1 << 27)
>>>  #define HWCAP_SSBS		(1 << 28)
>>> +#define HWCAP_SB		(1 << 29)
>>> +#define HWCAP_PACA		(1 << 30)
>>> +#define HWCAP_PACG		(1UL << 31)
>>
>> Note: we ran out of 32bit hwcaps, so further flags here
>> would not be compatible with ilp32 auxv.
>>
>> the plan is to introduce hwcap2 and keep adding flags
>> there, however that will require a change in ifunc
>> resolver abi if we want to pass down hwcap2.
>> i will try to come up with a fix for that in this
>> release cycle.
> 
> Yuck.  The last bit should have been used for indicating that
> additional IFUNC resolver information is available. 8-(

the ilp32 port passes uint64_t hwcap to the resolver currently
so the top 32bit can be used by glibc to signal the presence
of additional arguments to the resolver (this should work for
both lp64 and ilp32) however i havent worked out yet what
the additional argument should be (so it's extensible reasonably
in the future).

> 
> Is there still a way to fix this without requiring additional ABI
> symbols?
>