From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) by dpdk.org (Postfix) with ESMTP id 29ACEB6BA for ; Fri, 20 Feb 2015 15:31:58 +0100 (CET) Received: from orsmga003.jf.intel.com ([10.7.209.27]) by fmsmga101.fm.intel.com with ESMTP; 20 Feb 2015 06:31:38 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.09,614,1418112000"; d="scan'208";a="530375625" Received: from smonroyx-mobl.ger.corp.intel.com (HELO [10.237.221.3]) ([10.237.221.3]) by orsmga003.jf.intel.com with ESMTP; 20 Feb 2015 06:22:51 -0800 Message-ID: <54E74548.7010805@intel.com> Date: Fri, 20 Feb 2015 14:31:36 +0000 From: "Gonzalez Monroy, Sergio" User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: Neil Horman References: <91383E96CE459D47BCE92EFBF5CE73B004F45534@IRSMSX108.ger.corp.intel.com> <20150130181249.GC2664@hmsreliant.think-freely.org> <91383E96CE459D47BCE92EFBF5CE73B004F4AB9B@IRSMSX108.ger.corp.intel.com> <54DC70F3.4020902@redhat.com> <54DC7A87.1090208@intel.com> <20150212122354.GB8729@neilslaptop.think-freely.org> <54DCB3B6.1010204@redhat.com> <20150212155225.GB4634@neilslaptop.think-freely.org> <54DDCE68.7090400@redhat.com> <54DDDB12.3090100@intel.com> <20150213125142.GA11979@neilslaptop.think-freely.org> In-Reply-To: <20150213125142.GA11979@neilslaptop.think-freely.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: "dev@dpdk.org" Subject: Re: [dpdk-dev] [PATCH 0/8] Improve build process X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 20 Feb 2015 14:31:59 -0000 On 13/02/2015 12:51, Neil Horman wrote: > On Fri, Feb 13, 2015 at 11:08:02AM +0000, Gonzalez Monroy, Sergio wrote: >> On 13/02/2015 10:14, Panu Matilainen wrote: >>> On 02/12/2015 05:52 PM, Neil Horman wrote: >>>> On Thu, Feb 12, 2015 at 04:07:50PM +0200, Panu Matilainen wrote: >>>>> On 02/12/2015 02:23 PM, Neil Horman wrote: >>> [...snip...] >>>>>>>>> So I just realized that I was not having into account a possible >>>>>>>>> scenario, where >>>>>>>>> we have an app built with static dpdk libs then loading a dso >>>>>>>>> with -d >>>>>>>>> option. >>>>>>>>> >>>>>>>>> In such case, because the pmd would have DT_NEEDED entries, >>>>>>>>> dlopen will >>>>>>>>> fail. >>>>>>>>> So to enable such scenario we would need to build PMDs without >>>>>>>>> DT_NEEDED >>>>>>>>> entries. >>>>>>>> Hmm, for that to be a problem you'd need to have the PMD built >>>>>>>> against >>>>>>>> shared dpdk libs and while the application is built against >>>>>>>> static dpdk >>>>>>>> libs. I dont think that's a supportable scenario in any case. >>>>>>>> >>>>>>>> Or is there some other scenario that I'm not seeing? >>>>>>>> >>>>>>>> - Panu - >>>>>>>> >>>>>>> I agree with you. I suppose it comes down to, do we want to >>>>>>> support such >>>>>>> scenario? >>>>>>> >>>>>>> From what I can see, it seems that we do currently support such >>>>>>> scenario by >>>>>>> building dpdk apps against all static dpdk libs using >>>>>>> --whole-archive (all >>>>>>> libs and not only PMDs). >>>>>>> http://dpdk.org/browse/dpdk/commit/?id=20afd76a504155e947c770783ef5023e87136ad8 >>>>>>> >>>>>>> >>>>>>> Am I misunderstanding this? >>>>>>> >>>>>> Shoot, you're right, I missed the static build aspect to this. Yes, >>>>>> if we do the following: >>>>>> >>>>>> 1) Build the DPDK as a static library >>>>>> 2) Link an application against (1) >>>>>> 3) Use the dlopen mechanism to load a PMD built as a DSO >>>>>> >>>>>> Then the DT_NEEDED entries in the DSO will go unsatisfied, because >>>>>> the shared >>>>>> objects on which it (the PMD) depends will not exist in the file >>>>>> system. >>>>> I think its even more twisty: >>>>> >>>>> 1) Build the DPDK as a static library >>>>> 2) Link an application against (1) >>>>> 3) Do another build of DPDK as a shared library >>>>> 4) In app 2), use the dlopen mechanism to load a PMD built as a part >>>>> of or >>>>> against 3) >>>>> >>>>> Somehow I doubt this would work very well. >>>>> >>>> Ideally it should, presuming the ABI is preserved between (1) and (3), >>>> though I >>>> agree, up until recently, that was an assumption that was unreliable. >>> Versioning is a big and important step towards reliability but there are >>> more issues to solve. This of course getting pretty far from the original >>> topic, but at least one such issue is that there are some cases where a >>> config value affects what are apparently public structs (rte_mbuf wrt >>> RTE_MBUF_REFCNT for example), which really is a no-go. >>> >> Agree, the RTE_MBUF_REFCNT is something that needs to be dealt with asap. >> I'll look into it. >> >>>>>> I think the problem is a little bit orthogonal to the libdpdk_core >>>>>> problem you >>>>>> were initially addressing. That is to say, this problem of >>>>>> dlopen-ed PMD's >>>>>> exists regardless of weather you build the DPDK as part of a static >>>>>> or dynamic >>>>>> library. The problems just happen to intersect in their >>>>>> manipulation of the >>>>>> DT_NEEDED entries. >>>>>> >>>>>> Ok, so, given the above, I would say your approach is likely >>>>>> correct, just >>>>>> prevent DT_NEEDED entries from getting added to PMD's. Doing so will >>>>>> sidestep >>>>>> loading issue for libraries that may not exist in the filesystem, >>>>>> but thats ok, >>>>>> because by all rights, the symbols codified in those needed >>>>>> libraries should >>>>>> already be present in the running application (either made available >>>>>> by the >>>>>> application having statically linked them, or having the linker load >>>>>> them from >>>>>> the proper libraries at run time). >>>>> My 5c is that I'd much rather see the common case (all static or all >>>>> shared) >>>>> be simple and reliable, which in case of DSOs includes no lying >>>>> (whether by >>>>> omission or otherwise) about DT_NEEDED, ever. That way the issue is >>>>> dealt >>>>> once where it belongs. If somebody wants to go down the rabbit hole of >>>>> mixed >>>>> shared + static linkage, let them dig the hole by themselves :) >>>>> >>>> This is a fair point. Can DT_NEEDED sections be stripped via tools like >>>> objcopy >>>> after the build is complete? If so, end users can hack this corner case >>>> to work >>>> as needed. >>> Patchelf (http://nixos.org/patchelf.html) appears to support that, but >>> given that source is available it'd be easier to just modify the makefiles >>> if that's really needed. >>> >> I think we agree on the issue. >> >> So I'll be sending a patch to add DT_NEEDED entries to all libraries and >> PMDs. The only exception would be librte_eal, which would not have proper >> NEEDED entries. >> Do we bother adding a linker script for librte_eal that would include >> dependent libraries? >> > I say yes to the linker script, but will happily bow to an alternate consensus > Neil > So the case we want to solve is the following circular dependencies: eal -> mempool, malloc mempool -> eal , malloc, ring malloc -> eal ring -> eal, malloc We cannot write/create the proposed (below) linker script at least until we have built mempool and malloc. INPUT ( -lrte_eal.so -lrte_mempool -lrte_malloc ) Few ways I have thought about implementing this (not particularly fond of any of them) : - Have the linker script file in the repo (scripts/ ?) in a fixed location and just copy it to $(RTE_OUTPUT)/lib/ once all libs have finished building. - Generate the file on build time from a defined make variable once all libs have finished Thoughts? any other approached is more than welcome! Sergio PS: Thinking again on the core library and the issue of having multiple version.map files, we could have a core_version.map instead instead of multiple files per core library (eal, mempool, etc)