From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 109751 invoked by alias); 12 Mar 2015 11:31:45 -0000 Mailing-List: contact gdb-patches-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: gdb-patches-owner@sourceware.org Received: (qmail 109586 invoked by uid 89); 12 Mar 2015 11:31:44 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.8 required=5.0 tests=AWL,BAYES_00,SPF_HELO_PASS,SPF_PASS,T_RP_MATCHES_RCVD autolearn=ham version=3.3.2 X-HELO: mx1.redhat.com Received: from mx1.redhat.com (HELO mx1.redhat.com) (209.132.183.28) by sourceware.org (qpsmtpd/0.93/v0.84-503-g423c35a) with (AES256-GCM-SHA384 encrypted) ESMTPS; Thu, 12 Mar 2015 11:31:42 +0000 Received: from int-mx14.intmail.prod.int.phx2.redhat.com (int-mx14.intmail.prod.int.phx2.redhat.com [10.5.11.27]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id t2C4Ul2I016568 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL) for ; Thu, 12 Mar 2015 00:30:47 -0400 Received: from localhost (dhcp-10-15-16-169.yyz.redhat.com [10.15.16.169]) by int-mx14.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id t2C4UkQZ007024 (version=TLSv1/SSLv3 cipher=AES128-GCM-SHA256 bits=128 verify=NO); Thu, 12 Mar 2015 00:30:46 -0400 From: Sergio Durigan Junior To: Oleg Nesterov Cc: Jan Kratochvil , GDB Patches , Pedro Alves Subject: Re: [PATCH] Improve corefile generation by using /proc/PID/coredump_filter (PR corefile/16902) References: <878ufc9kau.fsf@redhat.com> <20150305154827.GA9441@host1.jankratochvil.net> <87zj7r5fpz.fsf@redhat.com> <20150305205744.GA13165@host1.jankratochvil.net> <20150311200052.GA22654@redhat.com> X-URL: http://blog.sergiodj.net Date: Thu, 12 Mar 2015 11:31:00 -0000 In-Reply-To: <20150311200052.GA22654@redhat.com> (Oleg Nesterov's message of "Wed, 11 Mar 2015 21:00:52 +0100") Message-ID: <87h9tqq1l5.fsf@redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-IsSubscribed: yes X-SW-Source: 2015-03/txt/msg00334.txt.bz2 On Wednesday, March 11 2015, Oleg Nesterov wrote: > On 03/05, Jan Kratochvil wrote: >> >> On Thu, 05 Mar 2015 21:52:56 +0100, Sergio Durigan Junior wrote: >> > On Thursday, March 05 2015, Jan Kratochvil wrote: >> > > On Thu, 05 Mar 2015 04:48:09 +0100, Sergio Durigan Junior wrote: >> > > Currently it also tries to dump [vvar] (by default rules) but that is >> > > unreadable for some reason, causing: >> > > warning: Memory read failed for corefile section, 8192 bytes at 0x7ffff6ceb000. >> > > ^^^^^^^^^^^^^^ >> > > Saved corefile /tmp/1j >> > > (gdb) _ >> > > # grep 7ffff6ceb000 /proc/$p/maps >> > > 7ffff6ceb000-7ffff6ced000 r--p 00000000 00:00 0 [vvar] >> > > ^^^^^^^^^^^^ ^^^^ >> > > >> > > I do not know what [vvar] is good for and why it cannot be read. > > Well, I am not sure I understand this new mapping correctly. I need to > recheck. > > But apparently it represents the kernel data (say, gtod) which vdso code > (running in user mode) can read. > > Probably gdb doesn't need to dump this vma, but see below. Right. As far as I can see this was not being dumped in the previous code, too. I did not check whether the Linux kernel dumps this or not. >> It would be good to get a reply from a kernel aware person what does it mean >> before such patch gets accepted. It can be also just a Linux kernel bug. > > _So far_ this doesn't look like a kernel bug to me. > > I guess it fails because of > > struct page *no_pages[] = {NULL}; > struct vm_special_mapping vvar_mapping = { > .name = "[vvar]", > .pages = no_pages, > }; > > so get_user_pages() -> special_mapping_fault() can't succeed, there is > no page it could return. > > And the code above looks as if we deny the access on purpose. Probably > this makes sense, this section can contain the "sensitive" data, say, > hpet timer's io memory... > > But! I need to recheck. In fact, it seems to me that I should discuss > this on lkml. I have some concerns, but most probably this is only my > misunderstanding, I need to read this (new to me) code more carefully. Thanks, Oleg. For now, I will keep discarding this mapping in the dumping. But please let us know about your findings. Meanwhile, I'll keep pinging this patch for reviews here. -- Sergio GPG key ID: 0x65FC5E36 Please send encrypted e-mail if possible http://sergiodj.net/