From owner-svn-src-all@freebsd.org Sun Aug 21 16:49:14 2016 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 522EDBC1ED1; Sun, 21 Aug 2016 16:49:14 +0000 (UTC) (envelope-from brde@optusnet.com.au) Received: from mail104.syd.optusnet.com.au (mail104.syd.optusnet.com.au [211.29.132.246]) by mx1.freebsd.org (Postfix) with ESMTP id 1AF87176A; Sun, 21 Aug 2016 16:49:13 +0000 (UTC) (envelope-from brde@optusnet.com.au) Received: from c122-106-149-109.carlnfd1.nsw.optusnet.com.au (c122-106-149-109.carlnfd1.nsw.optusnet.com.au [122.106.149.109]) by mail104.syd.optusnet.com.au (Postfix) with ESMTPS id 5E133427193; Mon, 22 Aug 2016 02:49:08 +1000 (AEST) Date: Mon, 22 Aug 2016 02:49:07 +1000 (EST) From: Bruce Evans X-X-Sender: bde@besplex.bde.org To: Slawa Olhovchenkov cc: Bruce Evans , Ed Schouten , src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r304555 - head/sys/compat/cloudabi In-Reply-To: <20160821135826.GB8192@zxy.spb.ru> Message-ID: <20160822022832.Q3214@besplex.bde.org> References: <201608210741.u7L7fBnN075023@repo.freebsd.org> <20160821105207.GS22212@zxy.spb.ru> <20160821210751.J2219@besplex.bde.org> <20160821120016.GZ8192@zxy.spb.ru> <20160821223255.K2478@besplex.bde.org> <20160821131447.GA8192@zxy.spb.ru> <20160821232721.G2639@besplex.bde.org> <20160821135826.GB8192@zxy.spb.ru> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed X-Optus-CM-Score: 0 X-Optus-CM-Analysis: v=2.1 cv=CoZCCSMD c=1 sm=1 tr=0 a=R/f3m204ZbWUO/0rwPSMPw==:117 a=L9H7d07YOLsA:10 a=9cW_t1CCXrUA:10 a=s5jvgZ67dGcA:10 a=kj9zAlcOel0A:10 a=Q4qeO4WkDawc_xgsBuMA:9 a=CjuIK1q_8ugA:10 X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.22 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: Sun, 21 Aug 2016 16:49:14 -0000 On Sun, 21 Aug 2016, Slawa Olhovchenkov wrote: > On Sun, Aug 21, 2016 at 11:39:02PM +1000, Bruce Evans wrote: > >> On Sun, 21 Aug 2016, Slawa Olhovchenkov wrote: >>> I am remeber about platforms with missaligment trap when >>> accessing int16 by odd address. Now platforms like this do not exist >>> anymore? >> >> i386 still exists, and it supports trapping on misalignement for at least >> CPL 3 (not kernel CPL 0). IIRC, amd64 drops support for this. > > Someone enable and support this? I am don't see. > May be PPC trap on this? > Alpha trap on this, but support of Alpha is droped. It is a 1-line change in asm (or a little more in C with #includes) to enable the trap: %%% #include #include #include int main(void) { char ch[5]; write_eflags(read_eflags() | PSL_AC); *(int *)&ch[0] = 0; *(int *)&ch[1] = 1; /* NOTREACHED */ } %%% This works on amd64 too after s/eflags/rflags. It is a trillion-line change to fix the compilers and applications to not do misaligned accesses :-). I only tried to use this ~25 years ago. Then the most obvious compiler bug was generating 32-bit acccesses to assign large but misaligned structs. If the compiler just generated calls to memcpy(), that might work, but in practice libraries also assume alignment. >>>> There are also endianness problems. The old version was even more broken >>>> on big endian systems. The current version needs some magic to reverse >>>> the memcpy() of the bits. We already depend on this for some 64-bit >>>> syscalls like lseek(). >>> >>> Can you explain some more? >>> This is not transfer over network and don't read from external media. >>> Where is problem? >> >> It is similar to a network transfer. It needs a protocol to pass values >> to applications. Type puns are fragile even within a single compilation >> unit. > > Application ad kernel run with same byte order, not? The application can do anything it wants, but has to translate if it uses the kernel or a library written in another language. Bruce