From: Alex Colomar <alx.manpages@gmail.com>
To: "GNU C Library" <libc-alpha@sourceware.org>,
"Bastien Roucariès" <rouca@debian.org>
Cc: Stefan Puiu <stefan.puiu@gmail.com>,
linux-man <linux-man@vger.kernel.org>,
gcc@gcc.gnu.org, Igor Sysoev <igor@sysoev.ru>,
Rich Felker <dalias@libc.org>,
Andrew Clayton <a.clayton@nginx.com>,
Richard Biener <richard.guenther@gmail.com>,
Zack Weinberg <zack@owlfolio.org>,
Florian Weimer <fweimer@redhat.com>,
Joseph Myers <joseph@codesourcery.com>,
Jakub Jelinek <jakub@redhat.com>
Subject: Re: struct sockaddr_storage
Date: Tue, 24 Jan 2023 19:00:31 +0100 [thread overview]
Message-ID: <e4a07ca9-f438-265d-c476-46843c6f3597@gmail.com> (raw)
In-Reply-To: <Y8633MfNxeI9StbW@tucnak>
[-- Attachment #1.1: Type: text/plain, Size: 1472 bytes --]
Hi,
After reading more about transparent_unit, here's my idea of a fix for
the API. old_api() is an example for the libc functions that accept a
`struct sockaddr *`, and user_code() is an example for user code
functions that handle sockaddr structures. The interface would be the
same as it is currently, but the implementation inside libc would change
to use a union. In user code, uses of sockaddr_storage would be made
safe with these changes, I believe, and new code would be simpler, since
it wouldn't need casts.
void old_api(union my_sockaddr_ptr *sa);
struct sockaddr_storage {
union {
struct {
sa_family_t ss_family;
};
struct sockaddr_in sin;
struct sockaddr_in6 sin6;
struct sockaddr_un sun;
// ...
};
};
union [[gnu::transparent_union]] sockaddr_ptr {
struct sockaddr_storage *ss;
struct sockaddr *sa;
};
void old_api(struct sockaddr_storage *ss)
{
// Here libc uses the union, so it doesn't invoke UB.
ss->sun.sa_family = AF_UNIX;
//...
}
void user_code(void)
{
struct my_sockaddr_storage ss; // object definition
// ...
old_api(&ss); // The transparent_union allows no casts.
switch (ss.ss_family) {
// This is safe too.
// thanks to common initial sequence within a union.
}
}
This would in fact deprecate plain `struct sockaddr`, as Bastien suggested.
Cheers,
Alex
--
<http://www.alejandro-colomar.es/>
[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 833 bytes --]
next prev parent reply other threads:[~2023-01-24 18:00 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-19 14:11 Alejandro Colomar
2023-01-20 10:06 ` Stefan Puiu
2023-01-20 12:39 ` Alejandro Colomar
2023-01-23 7:40 ` Stefan Puiu
2023-01-23 16:03 ` Alejandro Colomar
2023-01-23 16:28 ` Richard Biener
2023-01-24 16:38 ` Alex Colomar
2023-01-23 16:37 ` Jakub Jelinek
2023-01-24 16:40 ` Alex Colomar
2023-01-24 18:00 ` Alex Colomar [this message]
2023-01-24 11:16 ` Rich Felker
2023-01-24 16:53 ` Alex Colomar
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=e4a07ca9-f438-265d-c476-46843c6f3597@gmail.com \
--to=alx.manpages@gmail.com \
--cc=a.clayton@nginx.com \
--cc=dalias@libc.org \
--cc=fweimer@redhat.com \
--cc=gcc@gcc.gnu.org \
--cc=igor@sysoev.ru \
--cc=jakub@redhat.com \
--cc=joseph@codesourcery.com \
--cc=libc-alpha@sourceware.org \
--cc=linux-man@vger.kernel.org \
--cc=richard.guenther@gmail.com \
--cc=rouca@debian.org \
--cc=stefan.puiu@gmail.com \
--cc=zack@owlfolio.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).