Re: [PATCH] Add a new type attribute always_alias (PR79671)

[Florian Weimer <fweimer@redhat.com>]

On 04/06/2017 05:05 PM, Jakub Jelinek wrote:
> On Thu, Apr 06, 2017 at 04:51:01PM +0200, Florian Weimer wrote:
>> On 04/06/2017 04:43 PM, Jonathan Wakely wrote:
>>> On 06/04/17 16:23 +0200, Richard Biener wrote:
>>>> On Thu, 6 Apr 2017, Florian Weimer wrote:
>>>>
>>>>> On 04/06/2017 04:11 PM, Bernd Edlinger wrote:
>>>>>
>>>>>> I think it is not too complicated to done in the C++ FE.
>>>>>> The FE looks for array of std::byte and unsigned char,
>>>>>> and sets the attribute when the final type is constructed.
>>>>>>
>>>>>> What I am trying to do is just extend the semantic of may_alias
>>>>>> a bit, and then have the C++ FE use it in the way it has to.
>>>>>
>>>>> We also need this for some POSIX and Linux kernel interfaces.  A
>>>>> C++-only
>>>>> solution would not help with that.
>>>>
>>>> Example(s)?
>>>
>>> sockaddr_storage comes to mind.
>>
>> Right.  The kernel also has many APIs which return multiple variable-length
>> data blocks, such as getdents64, and many more interfaces in combination
>
> The kernel uses -fno-strict-aliasing I think, so it doesn't care.

These APIs (getdents64, inotify, lots of netlink stuff, probably more) 
extend to user space.

Thanks,
Florian