Date: Sat, 10 Oct 2015 12:24:33 +0000 From: Ed Maste <emaste@freebsd.org> To: Konstantin Belousov <kostikbel@gmail.com> Cc: Dimitry Andric <dim@freebsd.org>, "src-committers@freebsd.org" <src-committers@freebsd.org>, "svn-src-all@freebsd.org" <svn-src-all@freebsd.org>, "svn-src-head@freebsd.org" <svn-src-head@freebsd.org> Subject: Re: svn commit: r289072 - in head/contrib: libc++/src llvm/lib/Transforms/Vectorize Message-ID: <CAPyFy2BsS3Z7izEtWGqyXJkBcoykOX5y144w4Q997TKwWxaYDQ@mail.gmail.com> In-Reply-To: <20151010120311.GE2257@kib.kiev.ua> References: <201510091821.t99ILjHI054211@repo.freebsd.org> <20151010060846.GA2257@kib.kiev.ua> <CAPyFy2Dm=OaJbTfwVDABPz=e_H-XhhnTc%2BjYtr0iSHYv3uEObw@mail.gmail.com> <20151010120311.GE2257@kib.kiev.ua>
next in thread | previous in thread | raw e-mail | index | archive | help
On 10 October 2015 at 12:03, Konstantin Belousov <kostikbel@gmail.com> 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). >> 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
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?CAPyFy2BsS3Z7izEtWGqyXJkBcoykOX5y144w4Q997TKwWxaYDQ>