[RFC 2.0] Implementing hwcap2

[Richard Henderson]

On 2013-03-28 14:21, Ryan S. Arnold wrote:
> On Thu, Mar 28, 2013 at 1:06 PM, Richard Henderson <rth@twiddle.net> wrote:
>> On 03/28/2013 10:52 AM, Ryan Arnold wrote:
>>> +++ b/sysdeps/s390/s390-32/multiarch/ifunc-resolve.c
>>> @@ -19,6 +19,7 @@
>>>
>>>   #include <unistd.h>
>>>   #include <dl-procinfo.h>
>>> +#include <stdint.h>
>>>
>>>   #define STFLE_BITS_Z10  34 /* General instructions extension */
>>>   #define STFLE_BITS_Z196 45 /* Distinct operands, pop ... */
>>> @@ -38,7 +39,7 @@
>>>     extern void *FUNC##_z10 attribute_hidden;                          \
>>>     extern void *FUNC##_g5 attribute_hidden;                           \
>>>                                                                        \
>>> -  void *resolve_##FUNC (unsigned long int dl_hwcap)                  \
>>> +  void *resolve_##FUNC (uint64_t dl_hwcap)                           \
>>
>> This is an abi change for 32-bit big-endian systems.
>
> A uint64_t hwcap is already the default storage type for hwcap for all
> architectures.
>
>>From ldsodefs.h:
>
>    /* Mask for hardware capabilities that are available.  */
>    EXTERN uint64_t _dl_hwcap;
>
> Am I not understanding what you mean by 'abi change'?  Can you throw
> me a bone and describe a problematic use case where my suggestion
> breaks something?

Given "unsigned long int" = 32-bit and big-endian, e.g s390, then
currently the parameter is r2 = low(_dl_hwcap).

With your change, r2 = high(_dl_hwcap), r3 = low(_dl_hwcap).

You could preserve compatibility by changing the signature
to pass 32 bits per unsigned long argument, in an enforced
little-endian order.


r~