From: Alejandro Colomar <alx.manpages@gmail.com>
To: linux-man@vger.kernel.org
Cc: "Alejandro Colomar" <alx@kernel.org>, GCC <gcc@gcc.gnu.org>,
glibc <libc-alpha@sourceware.org>,
"Bastien Roucariès" <rouca@debian.org>,
"Stefan Puiu" <stefan.puiu@gmail.com>,
"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>,
"Eric Blake" <eblake@redhat.com>
Subject: [PATCH] sockaddr.3type: BUGS: Document that libc should be fixed using a union
Date: Sun, 5 Feb 2023 16:28:36 +0100 [thread overview]
Message-ID: <20230205152835.17413-1-alx@kernel.org> (raw)
As discussed before, and Bastien and I seem to agree, ideally we should
define the following types:
struct sockaddr_storage {
union {
struct {
sa_family_t ss_family;
};
struct sockaddr_in sin;
struct sockaddr_in6 sin6;
struct sockaddr_un sun;
// ...
};
};
struct [[deprecated]] sockaddr {
sa_family_t sa_family;
};
union [[gnu::transparent_union]] sockaddr_ptr {
struct sockaddr_storage *ss;
struct sockaddr *sa;
};
And then we could define APIs like:
int bind(int sockfd, const union sockaddr_ptr *addr, socklen_t len);
Link: <https://lore.kernel.org/linux-man/ab492040-2058-bcbe-c920-a9088a20f071@gmail.com/T/#u>
Link: <https://inbox.sourceware.org/libc-alpha/20230120134043.10247-1-alx@kernel.org/T/#u>
Cc: GCC <gcc@gcc.gnu.org>
Cc: glibc <libc-alpha@sourceware.org>
Cc: Bastien Roucariès <rouca@debian.org>
Cc: Stefan Puiu <stefan.puiu@gmail.com>
Cc: Igor Sysoev <igor@sysoev.ru>
Cc: Rich Felker <dalias@libc.org>
Cc: Andrew Clayton <a.clayton@nginx.com>
Cc: Richard Biener <richard.guenther@gmail.com>
Cc: Zack Weinberg <zack@owlfolio.org>
Cc: Florian Weimer <fweimer@redhat.com>
Cc: Joseph Myers <joseph@codesourcery.com>
Cc: Jakub Jelinek <jakub@redhat.com>
Cc: Eric Blake <eblake@redhat.com>
Signed-off-by: Alejandro Colomar <alx@kernel.org>
---
man3type/sockaddr.3type | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
diff --git a/man3type/sockaddr.3type b/man3type/sockaddr.3type
index 319a5e552..239e836fc 100644
--- a/man3type/sockaddr.3type
+++ 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,
+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),
--
2.39.1
next reply other threads:[~2023-02-05 15:30 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-05 15:28 Alejandro Colomar [this message]
2023-02-05 15:31 ` Alejandro Colomar
2023-02-06 6:02 ` Xi Ruoyao
2023-02-06 11:20 ` Rich Felker
2023-02-06 11:55 ` Alejandro Colomar
2023-02-06 13:38 ` Rich Felker
2023-02-06 14:11 ` Alejandro Colomar
2023-02-06 17:21 ` Zack Weinberg
2023-02-06 17:48 ` Rich Felker
2023-02-05 23:43 ` Rich Felker
2023-02-05 23:59 ` Alejandro Colomar
2023-02-06 0:15 ` Rich Felker
2023-02-06 18:45 ` Eric Blake
2023-02-07 1:21 ` Alejandro Colomar
2023-03-18 7:54 ` roucaries bastien
2023-03-20 10:49 ` Alejandro Colomar
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