From owner-svn-src-all@freebsd.org Sat Oct 10 12:53:54 2015 Return-Path: Delivered-To: svn-src-all@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 6A213A103BE; Sat, 10 Oct 2015 12:53:54 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (using TLSv1 with cipher DHE-RSA-CAMELLIA256-SHA (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id D2899855; Sat, 10 Oct 2015 12:53:53 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from tom.home (kostik@localhost [127.0.0.1]) by kib.kiev.ua (8.15.2/8.15.2) with ESMTPS id t9ACrmhV088128 (version=TLSv1 cipher=DHE-RSA-CAMELLIA256-SHA bits=256 verify=NO); Sat, 10 Oct 2015 15:53:49 +0300 (EEST) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.10.3 kib.kiev.ua t9ACrmhV088128 Received: (from kostik@localhost) by tom.home (8.15.2/8.15.2/Submit) id t9ACrmSE088127; Sat, 10 Oct 2015 15:53:48 +0300 (EEST) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Sat, 10 Oct 2015 15:53:48 +0300 From: Konstantin Belousov To: Ed Maste Cc: Dimitry Andric , "src-committers@freebsd.org" , "svn-src-all@freebsd.org" , "svn-src-head@freebsd.org" Subject: Re: svn commit: r289072 - in head/contrib: libc++/src llvm/lib/Transforms/Vectorize Message-ID: <20151010125348.GF2257@kib.kiev.ua> References: <201510091821.t99ILjHI054211@repo.freebsd.org> <20151010060846.GA2257@kib.kiev.ua> <20151010120311.GE2257@kib.kiev.ua> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) X-Spam-Status: No, score=-2.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FREEMAIL_FROM,NML_ADSP_CUSTOM_MED autolearn=no autolearn_force=no version=3.4.1 X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on tom.home X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 10 Oct 2015 12:53:54 -0000 On Sat, Oct 10, 2015 at 12:24:33PM +0000, Ed Maste wrote: > On 10 October 2015 at 12:03, Konstantin Belousov wrote: > >> The declaration is extern ostream cout; which correctly has 8 byte alignment. > > The alignment of the declaration does not matter, most likely. > > I am not sure what you mean by saying that 8 byte alignment is desirable, > > while compiler generates accesses (movdqa) which assume 16-byte alignment. > > I mean that this object is naturally expected to have 8-byte > alignment. In previous versions of libc++.so shipped with FreeBSD it > did, and can't be changed now (cout comes from the binary itself, via > a copy relocation). No, the natural alignment for char[] is 1, while ABI requires an array longer than 15 bytes to have 16-bytes alignment. > > >> In the implementation (contrib/libc++/src/iostream.cpp) it is defined > >> as a char array which is where the 16-byte ABI alignment would arise, > >> but explicitly specifies 8-byte alignment: > >> _ALIGNAS_TYPE (ostream) _LIBCPP_FUNC_VIS char cout[sizeof(ostream)]; > >> > >> Compiling with -emit-llvm --save-temps shows the desired 8-byte > >> alignment for cout in the LLVM IR but 16-byte in the assembly file. > > Could somebody show the readelf -s iostream.So and readelf -s libc++.so.X > > output lines for the symbol, please ? > > readelf -s iostream.So: > 120: 0000000000000150 160 OBJECT GLOBAL DEFAULT 5 _ZNSt3__14coutE > > libc++.so.1.full > 1280: 00000000002bb4a0 160 OBJECT GLOBAL DEFAULT 25 _ZNSt3__14coutE And there the object has right alignment.