From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7214AC47258 for ; Fri, 1 May 2020 06:00:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5BEC9208DB for ; Fri, 1 May 2020 06:00:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728241AbgEAGAg (ORCPT ); Fri, 1 May 2020 02:00:36 -0400 Received: from mail.kernel.org ([198.145.29.99]:35320 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726452AbgEAGAg (ORCPT ); Fri, 1 May 2020 02:00:36 -0400 Received: from [192.168.0.106] (unknown [202.53.39.250]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id BE2482070B; Fri, 1 May 2020 06:00:30 +0000 (UTC) Subject: Re: [PATCH v2 0/5] Fix ELF / FDPIC ELF core dumping, and use mmap_sem properly in there To: Rich Felker Cc: Linus Torvalds , Russell King - ARM Linux admin , Jann Horn , Nicolas Pitre , Andrew Morton , Christoph Hellwig , Linux Kernel Mailing List , Linux-MM , linux-fsdevel , Alexander Viro , "Eric W . Biederman" , Oleg Nesterov , Linux ARM , Mark Salter , Aurelien Jacquiot , linux-c6x-dev@linux-c6x.org, Yoshinori Sato , Linux-sh list References: <20200429214954.44866-1-jannh@google.com> <20200429215620.GM1551@shell.armlinux.org.uk> <31196268-2ff4-7a1d-e9df-6116e92d2190@linux-m68k.org> <20200430145123.GE21576@brightrain.aerifal.cx> From: Greg Ungerer Message-ID: <6dd187b4-1958-fc40-73c4-3de53ed69a1e@linux-m68k.org> Date: Fri, 1 May 2020 16:00:28 +1000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200430145123.GE21576@brightrain.aerifal.cx> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 1/5/20 12:51 am, Rich Felker wrote: > On Fri, May 01, 2020 at 12:10:05AM +1000, Greg Ungerer wrote: >> >> >> On 30/4/20 9:03 am, Linus Torvalds wrote: >>> On Wed, Apr 29, 2020 at 2:57 PM Russell King - ARM Linux admin >>> wrote: >>>> >>>> I've never had any reason to use FDPIC, and I don't have any binaries >>>> that would use it. Nicolas Pitre added ARM support, so I guess he >>>> would be the one to talk to about it. (Added Nicolas.) >>> >>> While we're at it, is there anybody who knows binfmt_flat? >>> >>> It might be Nicolas too. >>> >>> binfmt_flat doesn't do core-dumping, but it has some other oddities. >>> In particular, I'd like to bring sanity to the installation of the new >>> creds, and all the _normal_ binfmt cases do it largely close together >>> with setup_new_exec(). >>> >>> binfmt_flat is doing odd things. It's doing this: >>> >>> /* Flush all traces of the currently running executable */ >>> if (id == 0) { >>> ret = flush_old_exec(bprm); >>> if (ret) >>> goto err; >>> >>> /* OK, This is the point of no return */ >>> set_personality(PER_LINUX_32BIT); >>> setup_new_exec(bprm); >>> } >>> >>> in load_flat_file() - which is also used to loading _libraries_. Where >>> it makes no sense at all. >> >> I haven't looked at the shared lib support in there for a long time, >> but I thought that "id" is only 0 for the actual final program. >> Libraries have a slot or id number associated with them. > > This sounds correct. My understanding of FLAT shared library support > is that it's really bad and based on having preassigned slot indices > for each library on the system, and a global array per-process to give > to data base address for each library. Libraries are compiled to know > their own slot numbers so that they just load from fixed_reg[slot_id] > to get what's effectively their GOT pointer. > > I'm not sure if anybody has actually used this in over a decade. Last > time I looked the tooling appeared broken, but in this domain lots of > users have forked private tooling that's not publicly available or at > least not publicly indexed, so it's hard to say for sure. Be at least 12 or 13 years since I last had a working shared library build for m68knommu. I have not bothered with it since then, not that I even used it much when it worked. Seemed more pain than it was worth. Regards Greg