From mboxrd@z Thu Jan 1 00:00:00 1970 X-Msuck: nntp://news.gmane.org/gmane.linux.lib.musl.general/9883 Path: news.gmane.org!not-for-mail From: Sebastian Gottschall Newsgroups: gmane.linux.lib.musl.general Subject: Re: recvmsg/sendmsg broken on mips64 Date: Mon, 11 Apr 2016 00:24:49 +0200 Message-ID: References: <20160401113146.GU9862@port70.net> <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=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Trace: ger.gmane.org 1460327096 14512 80.91.229.3 (10 Apr 2016 22:24:56 GMT) X-Complaints-To: usenet@ger.gmane.org NNTP-Posting-Date: Sun, 10 Apr 2016 22:24:56 +0000 (UTC) To: musl@lists.openwall.com Original-X-From: musl-return-9896-gllmg-musl=m.gmane.org@lists.openwall.com Mon Apr 11 00:24:55 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 1apNml-0002qP-FW for gllmg-musl@m.gmane.org; Mon, 11 Apr 2016 00:24:51 +0200 Original-Received: (qmail 22330 invoked by uid 550); 10 Apr 2016 22:24:48 -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 22312 invoked from network); 10 Apr 2016 22:24:48 -0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=dd-wrt.com; s=mikd; h=Subject:Content-Transfer-Encoding:Content-Type:In-Reply-To:MIME-Version:Date:Message-ID:From:References:To; bh=7JgEHCSAWIgoFHBYdOUal7BammiSBCgDSGSefxI1CnA=; b=jTvsocpnJulIGcsJRaoVHuzbHMG3TdCPFTInCFIjMeymqcn/G42NOyr3VEkSslXprLpWonL2yptJbcpxVfnSGhKMM6+w0QFFvplqPwyJy23VnDlGnorIWC6nwX6lNNk5NSHUhlasVHrHxUID8FlAopvGX04AJAuFIR3IzY9cymA=; User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.0 In-Reply-To: <20160410221812.GP21636@brightrain.aerifal.cx> X-SA-Exim-Connect-IP: 217.234.132.69 X-SA-Exim-Mail-From: s.gottschall@dd-wrt.com X-Spam-Checker-Version: SpamAssassin 3.1.9 (2007-02-13) on webmail.newmedia-net.de X-Spam-Level: X-Spam-Status: No, score=-2.5 required=4.0 tests=ALL_TRUSTED,BAYES_00, DNS_FROM_AHBL_RHSBL,RATWARE_GECKO_BUILD autolearn=no version=3.1.9, No X-SA-Exim-Version: 4.2.1 (built Thu, 26 May 2011 15:22:33 +0200) X-SA-Exim-Scanned: Yes (on webmail.newmedia-net.de) X-NMN-MailScanner-Information: Please contact the ISP for more information X-NMN-MailScanner-ID: 1apNmV-0003SZ-8r X-NMN-MailScanner: Found to be clean X-NMN-MailScanner-From: s.gottschall@dd-wrt.com X-Received: from [217.234.132.69] (helo=[10.88.193.128]) by webmail.newmedia-net.de with esmtpsa (TLSv1:AES128-SHA:128) (Exim 4.72) (envelope-from ) id 1apNmV-0003SZ-8r for musl@lists.openwall.com; Mon, 11 Apr 2016 00:24:35 +0200 Xref: news.gmane.org gmane.linux.lib.musl.general:9883 Archived-At: Am 11.04.2016 um 00:18 schrieb Rich Felker: > On Fri, Apr 08, 2016 at 01:33:51AM +0200, Sebastian Gottschall wrote: >> Am 07.04.2016 um 20:46 schrieb Szabolcs Nagy: >>> * Sebastian Gottschall [2016-04-07 13:42:17 +0200]: >>>>> ok so the failure is in sendmsg and in the msg_control copy. >>>>> >>>>> does the call fail with ENOMEM (because >1024 bytes of ancillary data)? >>>>> that would be easy to fix.. >>>>> >>>>> (libc has to make a copy, the struct is const and might be in >>>>> readonly memory. a detailed bug report of the failure would >>>>> be more useful than speculations about broken compilers.. >>>>> e.g. strace log with and without the msg_control copying.) >>>> how to make a more detailed report than just that all netlink operations in >>>> iproute2 fail. so the whole ip command doesnt work. >>> there are only two places where msg->msg_control >>> is used in iproute2: bpf_scm.h and libnetlink.c, >>> they both use a fixed char[1024] buffer, which >>> should work with musl. >>> >>> one thing i noticed is that iproute2 fails to >>> take cmsghdr alignment requirements into account, >>> so it only works by accident. >>> >>> i think the musl struct has different alignment >>> (4 byte instead of 8 byte) which may cause problems >>> because the copy uses the musl alignment, i'm >>> not sure if this can cause what you observed. >>> >>> so we still don't know what your problem was >>> and what fails exactly. >> easy again. iproute2 doesnt work on mips64 targets since recvmsg / >> sendmsg call does fail, caused by a wrong structure alignment, bad >> structure at all or bad musl code at all. > 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 > >> 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. > > Rich >