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

[roucaries bastien <roucaries.bastien+debian@gmail.com>]

Hi,

I have opened a defect at austin group
https://www.austingroupbugs.net/view.php?id=1641

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
>