From owner-svn-src-head@freebsd.org Mon Aug 22 08:56:04 2016 Return-Path: Delivered-To: svn-src-head@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 3C3BBBC0578; Mon, 22 Aug 2016 08:56:04 +0000 (UTC) (envelope-from brde@optusnet.com.au) Received: from mail109.syd.optusnet.com.au (mail109.syd.optusnet.com.au [211.29.132.80]) by mx1.freebsd.org (Postfix) with ESMTP id 0374C1190; Mon, 22 Aug 2016 08:56:03 +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 mail109.syd.optusnet.com.au (Postfix) with ESMTPS id 39848D67B69; Mon, 22 Aug 2016 18:55:58 +1000 (AEST) Date: Mon, 22 Aug 2016 18:55:58 +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: <20160821170611.GC8192@zxy.spb.ru> Message-ID: <20160822184056.M1897@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> <20160822022832.Q3214@besplex.bde.org> <20160821170611.GC8192@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=VIkg5I7X 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=kc8NhsJuO7BAuJf6d58A:9 a=CjuIK1q_8ugA:10 X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.22 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 22 Aug 2016 08:56:04 -0000 On Sun, 21 Aug 2016, Slawa Olhovchenkov wrote: > On Mon, Aug 22, 2016 at 02:49:07AM +1000, Bruce Evans wrote: > >> 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: > > OK, we can turn amd64 in this mode. > And cat do request to kernel with unalligned access, this cause trap > and panic, yes? No. PSL_AC is ignored in kernel mode. >> 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. > > This issuse can be trigerred and by two-bytes assigmen, yes? Not quite that short. i386 has the 1-byte cli instruction for conveniently setting the interrupt enable flag, but setting PSL_AC seems to take at least 3 instructions and 6-7 bytes (pushf; orb $N,$M(%[re][bs]p); popf). >>>>>> 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. > > You talk about different byte order in differenr languages? Could be, or the same language with a different ABI. Bruce