From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/9884 Path: news.gmane.org!not-for-mail From: Rich Felker Newsgroups: gmane.linux.lib.musl.general Subject: Re: recvmsg/sendmsg broken on mips64 Date: Sun, 10 Apr 2016 18:29:47 -0400 Message-ID: <20160410222947.GQ21636@brightrain.aerifal.cx> References: <91bfe81c-73c4-9b25-6d9b-a97d4ee54e89@dd-wrt.com> <20160401131712.GV9862@port70.net> <4445e7a7-19f3-aa7c-04dc-3e329ef7fdac@dd-wrt.com> <20160407094806.GE9862@port70.net> <20160407184643.GI9862@port70.net> <2656e404-f225-cd95-3989-a48df486d914@dd-wrt.com> <20160410221812.GP21636@brightrain.aerifal.cx> Reply-To: musl@lists.openwall.com NNTP-Posting-Host: plane.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: ger.gmane.org 1460327404 18847 80.91.229.3 (10 Apr 2016 22:30:04 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 10 Apr 2016 22:30:04 +0000 (UTC) To: musl@lists.openwall.com Original-X-From: musl-return-9897-gllmg-musl=m.gmane.org@lists.openwall.com Mon Apr 11 00:30:04 2016 Return-path: Envelope-to: gllmg-musl@m.gmane.org Original-Received: from mother.openwall.net ([195.42.179.200]) by plane.gmane.org with smtp (Exim 4.69) (envelope-from ) id 1apNrn-0004rH-As for gllmg-musl@m.gmane.org; Mon, 11 Apr 2016 00:30:03 +0200 Original-Received: (qmail 26066 invoked by uid 550); 10 Apr 2016 22:30:00 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Original-Received: (qmail 26045 invoked from network); 10 Apr 2016 22:30:00 -0000 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Original-Sender: Rich Felker Xref: news.gmane.org gmane.linux.lib.musl.general:9884 Archived-At: On Mon, Apr 11, 2016 at 12:24:49AM +0200, Sebastian Gottschall wrote: > >I think what nsz was asking for, and what I'd like to see, is a way to > >reproduce the bug. I'm going to try building iproute2 for mips64 and > >running it on a prebuilt kernel from Aboriginal Linux under > >qemu-system-mips64, but I don't know what specific commands are needed > >to hit the affected code path. > any command since all is netlink based > ip add add 192.168.1.1/24 dev eth0 > > yo will see that nothing will happen. ip will just return a error > message (i wrote this message already in the first entry on this > mailinglist) > "EOF on netlink" is the error which is shown OK, I'll try this. > >>its all resulting in the same failing recvmsg / sendmsg call.. so > >>yes libnetlink.c does not work with musl on mips64 (it does work on > >>x64 and everything else, just not mips64) unless the hack i offered > >>was applied which again fixed all. > >>before you ask again for a problem description, just read again. it > >>wont change the description if you ask again and just makes people > >>tired on this list. > >Both versions of the struct (musl's and your modified one that matches > >the kernel) have the exact same layout, but due to having a member > >with 64-bit type, yours has 8-byte alignment and musl's only has > >4-byte alignment. This means, at least: > > > >1. When musl's sendmsg.c makes its copy to zero out the padding, the > > copy may not be correctly aligned for 64-bit writes, and the kernel > > faults or manually produces an error for this case, causing the > > whole operation to fail. However, I don't see where iproute2 is > > actually passing control messages to sendmsg, so while this is a > > problem, I don't think it's the cause. Maybe I'm missing the > > affected call point; this is why I'd like steps to reproduce the > > issue so I can see it. > > > >2. iproute2's libnetlink.c's rtnl_listen function does not properly > > declare its cmsgbuf with the alignment of cmsghdr; it has type > > char[] so the compiler is free not to align it at all. This is > > presumably a bug in iproute2, but I can't find any good > > documentation (in the standards or Linux-specific) for how you're > > supposed to allocate this space, so maybe the kernel is able to > > handle aligning the buffer itself. I don't see any way the > > alignment of musl's cmsghdr type affects recvmsg though. > > > >Maybe there are other effects I'm missing? I'll follow up again once I > >get a test build/run of iproute2 and let you know whether I can see > >the problem. > okay. if you need a remote access to a octeon system using musl (my > fixed variant), just tell me. That would be really helpful. Something's wrong with the userspace for the Aboriginal mips64 binaries (SIGBUS in init) and debugging that would be a big distraction. BTW do you have gdb and strace available? Rich