Re: [PATCH] sockaddr.3type: BUGS: Document that libc should be fixed using a union

[Alejandro Colomar <alx.manpages@gmail.com>]

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Hi Bastien and Eric!

On 3/18/23 08:54, roucaries bastien wrote:
> Hi,
> 
> I have opened a defect at austin group
> https://www.austingroupbugs.net/view.php?id=1641

Sorry for not having prepared yet my report as I promised to Eric.
I've been busy with other stuff, but still had in mind doing it :).
But yes, basically that report is what I would have written, so you
have my +1.  ;)

Cheers,

Alex

> 
> Bastien
> 
> Le lun. 6 févr. 2023 à 18:45, Eric Blake <eblake@redhat.com> a écrit :
>>
>> On Sun, Feb 05, 2023 at 04:28:36PM +0100, Alejandro Colomar wrote:
>>
>> Regardless of the merits of the patch, let's not introduce typos:
>>
>>> +++ b/man3type/sockaddr.3type
>>> @@ -120,6 +120,26 @@ .SH NOTES
>>>  .I <netinet/in.h>
>>>  and
>>>  .IR <sys/un.h> .
>>> +.SH BUGS
>>> +.I sockaddr_storage
>>> +was designed back when strict aliasing wasn't a problem.
>>> +Back then,
>>> +one would define a variable of that type,
>>> +and then access it as any of the other
>>> +.IR sockaddr_ *
>>> +types,
>>> +depending on the value of the first member.
>>> +This is Undefined Behavior.
>>> +However, there is no way to use these APIs without invoking Unedfined Behavior,
>>
>> Undefined
>>
>>> +either in the user program or in libc,
>>> +so it is still recommended to use this method.
>>> +The only correct way to use different types in an API is through a union.
>>> +However,
>>> +that union must be implemented in the library,
>>> +since the type must be shared between the library and user code,
>>> +so libc should be fixed by implementing
>>> +.I sockaddr_storage
>>> +as a union.
>>>  .SH SEE ALSO
>>>  .BR accept (2),
>>>  .BR bind (2),
>>
>> Also, while I could raise the issue with the Austin Group on your
>> behalf to get the POSIX wording improved, I think it would work better
>> if you initiate a bug report rather than having me do it:
>>
>> https://www.austingroupbugs.net/main_page.php
>>
>> --
>> Eric Blake, Principal Software Engineer
>> Red Hat, Inc.           +1-919-301-3266
>> Virtualization:  qemu.org | libvirt.org
>>

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