From patchwork Sun Feb 5 15:28:36 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Alejandro Colomar X-Patchwork-Id: 64328 Return-Path: X-Original-To: patchwork@sourceware.org Delivered-To: patchwork@sourceware.org Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id E79C53858417 for ; Sun, 5 Feb 2023 15:30:46 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org E79C53858417 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sourceware.org; s=default; t=1675611046; bh=VU2zRmdDezhcg1tV1N9BKQByb+mc/HyDCQKGJKdaU84=; h=To:Cc:Subject:Date:List-Id:List-Unsubscribe:List-Archive: List-Post:List-Help:List-Subscribe:From:Reply-To:From; b=LCpzbptjpCLVfe49xtV7WrEbJNfNxHTNH7++myk9tXqzdcH/Zf0vPfd7vBrKm1IhD B/dKO8MpuTB8i1+7AtXiPvqIUKCSx0BUZrQilDE4em6l4Dl2aIsoNPrh/vePUEPQSs UiZ5dQrl2OB2NG0hI8r8QFgFySnzpfGsiH1zCqGQ= X-Original-To: libc-alpha@sourceware.org Delivered-To: libc-alpha@sourceware.org Received: from mail-wr1-x436.google.com (mail-wr1-x436.google.com [IPv6:2a00:1450:4864:20::436]) by sourceware.org (Postfix) with ESMTPS id 09CAA3858D32 for ; 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Sun, 05 Feb 2023 07:30:22 -0800 (PST) Received: from asus5775.alejandro-colomar.es ([170.253.36.171]) by smtp.googlemail.com with ESMTPSA id b12-20020adff90c000000b002c3e89039casm914150wrr.12.2023.02.05.07.30.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 05 Feb 2023 07:30:22 -0800 (PST) X-Google-Original-From: Alejandro Colomar To: linux-man@vger.kernel.org Cc: Alejandro Colomar , GCC , glibc , =?utf-8?q?Bastien_Roucari=C3=A8s?= , Stefan Puiu , Igor Sysoev , Rich Felker , Andrew Clayton , Richard Biener , Zack Weinberg , Florian Weimer , Joseph Myers , Jakub Jelinek , Eric Blake Subject: [PATCH] sockaddr.3type: BUGS: Document that libc should be fixed using a union Date: Sun, 5 Feb 2023 16:28:36 +0100 Message-Id: <20230205152835.17413-1-alx@kernel.org> X-Mailer: git-send-email 2.39.1 MIME-Version: 1.0 X-Spam-Status: No, score=-10.4 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, GIT_PATCH_0, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-Patchwork-Original-From: Alejandro Colomar via Libc-alpha From: Alejandro Colomar Reply-To: Alejandro Colomar Errors-To: libc-alpha-bounces+patchwork=sourceware.org@sourceware.org Sender: "Libc-alpha" 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: Link: Cc: GCC Cc: glibc Cc: Bastien Roucariès Cc: Stefan Puiu Cc: Igor Sysoev Cc: Rich Felker Cc: Andrew Clayton Cc: Richard Biener Cc: Zack Weinberg Cc: Florian Weimer Cc: Joseph Myers Cc: Jakub Jelinek Cc: Eric Blake Signed-off-by: Alejandro Colomar --- 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 and .IR . +.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),