From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5] helo=mx0a-001b2d01.pphosted.com) by bombadil.infradead.org with esmtps (Exim 4.85_2 #1 (Red Hat Linux)) id 1c9Ni2-0003Yx-SE for kexec@lists.infradead.org; Wed, 23 Nov 2016 02:54:56 +0000 Received: from pps.filterd (m0098416.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.17/8.16.0.17) with SMTP id uAN2s75f045313 for ; Tue, 22 Nov 2016 21:54:33 -0500 Received: from e24smtp01.br.ibm.com (e24smtp01.br.ibm.com [32.104.18.85]) by mx0b-001b2d01.pphosted.com with ESMTP id 26vku9j3gk-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Tue, 22 Nov 2016 21:54:32 -0500 Received: from localhost by e24smtp01.br.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 23 Nov 2016 00:54:30 -0200 Received: from d24relay03.br.ibm.com (d24relay03.br.ibm.com [9.18.232.225]) by d24dlp01.br.ibm.com (Postfix) with ESMTP id 58267352006C for ; Tue, 22 Nov 2016 21:53:59 -0500 (EST) Received: from d24av05.br.ibm.com (d24av05.br.ibm.com [9.18.232.44]) by d24relay03.br.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id uAN2sSYF39321606 for ; Wed, 23 Nov 2016 00:54:28 -0200 Received: from d24av05.br.ibm.com (localhost [127.0.0.1]) by d24av05.br.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id uAN2sR5P015016 for ; Wed, 23 Nov 2016 00:54:28 -0200 From: Thiago Jung Bauermann Subject: Re: [PATCH v10 04/10] kexec_file: Add support for purgatory built as PIE. Date: Wed, 23 Nov 2016 00:54:20 -0200 In-Reply-To: <20161123013258.GA3222@dhcp-128-65.nay.redhat.com> References: <1478748449-3894-1-git-send-email-bauerman@linux.vnet.ibm.com> <2486176.qfzlYnJWAn@morokweng> <20161123013258.GA3222@dhcp-128-65.nay.redhat.com> MIME-Version: 1.0 Message-Id: <1600863.ghUE1ReoOW@morokweng> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: Dave Young Cc: Stewart Smith , Stephen Rothwell , "H. Peter Anvin" , Baoquan He , Michael Ellerman , x86@kernel.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, Ingo Molnar , Paul Mackerras , Eric Biederman , Benjamin Herrenschmidt , Thomas Gleixner , Mimi Zohar , linuxppc-dev@lists.ozlabs.org, Andrew Morton , Vivek Goyal Am Mittwoch, 23. November 2016, 09:32:58 BRST schrieb Dave Young: > On 11/22/16 at 11:44am, Thiago Jung Bauermann wrote: > > Am Dienstag, 22. November 2016, 17:01:10 BRST schrieb Michael Ellerman: > > > Thiago Jung Bauermann writes: > > > > Am Sonntag, 20. November 2016, 10:45:46 BRST schrieb Dave Young: > > > >> On 11/10/16 at 01:27am, Thiago Jung Bauermann wrote: > > > >> > powerpc's purgatory.ro has 12 relocation types when built as > > > >> > a relocatable object. To implement support for them requires > > > >> > arch_kexec_apply_relocations_add to duplicate a lot of code with > > > >> > module_64.c:apply_relocate_add. > > > >> > > > > >> > When built as a Position Independent Executable there are only 4 > > > >> > relocation types in purgatory.ro, so it becomes practical for the > > > >> > powerpc > > > >> > implementation of kexec_file to have its own relocation > > > >> > implementation. > > > >> > > > > >> > Also, the purgatory is an executable and not an intermediary output > > > >> > from > > > >> > the compiler so it makes sense conceptually that it is easier to > > > >> > build > > > >> > it as a PIE than as a partially linked object. > > > >> > > > > >> > Apart from the greatly reduced number of relocations, there are two > > > >> > differences between a relocatable object and a PIE: > > > >> > > > > >> > 1. __kexec_load_purgatory needs to use the program headers rather > > > >> > than > > > >> > the > > > >> > > > > >> > section headers to figure out how to load the binary. > > > >> > > > > >> > 2. Symbol values are absolute addresses instead of relative to the > > > >> > > > > >> > start of the section. > > > >> > > > > >> > This patch adds the support needed in generic code for the > > > >> > differences > > > >> > above and allows powerpc to load and relocate a position > > > >> > independent > > > >> > purgatory. > > > >> > > > >> [snip] > > > >> > > > >> The kexec-tools machine_apply_elf_rel is pretty simple for ppc64, it > > > >> is > > > >> not that complex. So could you look into simplify your kexec_file > > > >> implementation? > > > > > > > > I can try, but there is one fundamental issue here: powerpc > > > > position-dependent code relies more on relocations than x86 > > > > position-dependent code does, so there's a limit to how simple it can > > > > be > > > > made without switching to position- independent code. And it will > > > > always > > > > be more involved than it is on x86. > > > > > > I think we need to go back to the drawing board on this one. > > > > > > My hope was that building purgatory as PIE would reduce the amount of > > > complexity, but instead it's just added more. Sorry for sending you in > > > that direction. > > > > It added complexity because in my series powerpc was using a PIE purgatory > > but x86 kept using a partially-linked object (because of the problem I > > mentioned I had when trying out a PIE x86 purgatory), so generic code > > needed two purgatory loaders. > > > > I'll see if I can make the PIE x86 purgatory to work so that generic code > > can have only one loader implementation. Then it will indeed be simpler. > Do we really need the PIE purgatory, after moving generic code out of > x86, there will be no much benefit, no? It still makes a big difference on powerpc, even after moving out the generic code. I just got the PIE purgatory working on x86 and it also simplifies the code there, so it's a win for both architectures. I'll clean up the code and post tomorrow so that you can see what you think. > Anyway, the first step should be > making the purgatory code more generic so that it can be easier for > other arches to support kexec_file in the future. I'll try putting sha256.c in lib/purgatory/ as you suggested. -- Thiago Jung Bauermann IBM Linux Technology Center _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec