From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753080AbcHOX0D (ORCPT ); Mon, 15 Aug 2016 19:26:03 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:50889 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752408AbcHOX0B (ORCPT ); Mon, 15 Aug 2016 19:26:01 -0400 X-IBM-Helo: d24dlp01.br.ibm.com X-IBM-MailFrom: bauerman@linux.vnet.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org From: Thiago Jung Bauermann To: bsingharora@gmail.com Cc: kexec@lists.infradead.org, Stewart Smith , Benjamin Herrenschmidt , Baoquan He , linuxppc-dev@lists.ozlabs.org, x86@kernel.org, "H. Peter Anvin" , linux-kernel@vger.kernel.org, Ingo Molnar , Paul Mackerras , Eric Biederman , Michael Ellerman , Thomas Gleixner , Dave Young , Andrew Morton , Vivek Goyal Subject: Re: [PATCH v5 04/13] powerpc: Factor out relocation code from module_64.c to elf_util_64.c. Date: Mon, 15 Aug 2016 20:25:51 -0300 User-Agent: KMail/4.14.3 (Linux/3.13.0-93-generic; KDE/4.14.13; x86_64; ; ) In-Reply-To: <20160815074634.GC21080@balbir.ozlabs.ibm.com> References: <1470956898-5991-1-git-send-email-bauerman@linux.vnet.ibm.com> <1470956898-5991-5-git-send-email-bauerman@linux.vnet.ibm.com> <20160815074634.GC21080@balbir.ozlabs.ibm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16081523-0032-0000-0000-000002758BDD X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16081523-0033-0000-0000-00000EBBA780 Message-Id: <4126991.2tm6WB17SD@hactar> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-08-15_10:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=1 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1604210000 definitions=main-1608150264 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Am Montag, 15 August 2016, 17:46:34 schrieb Balbir Singh: > On Thu, Aug 11, 2016 at 08:08:09PM -0300, Thiago Jung Bauermann wrote: > > +/** > > + * elf64_apply_relocate_add - apply 64 bit RELA relocations > > + * @elf_info: Support information for the ELF binary being relocated. > > + * @strtab: String table for the associated symbol table. > > + * @symindex: Section header index for the associated symbol table. > > + * @relsec: Section header index for the relocations to apply. > > + * @obj_name: The name of the ELF binary, for information messages. > > + */ > > +int elf64_apply_relocate_add(const struct elf_info *elf_info, > > + const char *strtab, unsigned int symindex, > > + unsigned int relsec, const char *obj_name) > > +{ > > + unsigned int i; > > + Elf64_Shdr *sechdrs = elf_info->sechdrs; > > + Elf64_Rela *rela = (void *)sechdrs[relsec].sh_addr; > > + Elf64_Sym *sym; > > + unsigned long *location; > > + unsigned long value; > > + > > For the relocatable kernel we expect only > > R_PPC64_RELATIVE > R_PPC64_NONE > R_PPC64_ADDR64 > > In the future we can use this to check/assert the usage of this > for the core kernel (vmlinux) when loaded. > > Did we check elf64_apply_relocate_add with zImage and vmlinux? kexec_file_load doesn't call call elf64_apply_relocate_add on the kernel image, it only uses it to relocate the purgatory. So whether it is loading a zImage or a vmlinux file, the function will work in the same way since the purgatory binary is the same regardless of the kernel image format. For the same reason, as it currently stands kexec_file_load can't check the relocation types used in the kernel image. But it is possible to add such a check/assertion in kexec_elf_64.c:build_elf_exec_info if we want. I tested kexec_file_load on both relocatable and non-relocatable vmlinux and it works correctly. I hadn't tested with zImage yet. I just did, and I had two problems: 1. For some reason, it has an INTERP segment. This patch series doesn't support loading program interpreters for ELF binaries, so kexec_elf_64.c:build_elf_exec_info refuses to load them. 2. If I disable the check for the INTERP segment, the zImage file loads correctly, but then I get an exception during reboot when loading the kexec image, right before jumping into the purgatory. I suspect this is because the LOAD segment has a virtual address of 0, and the first kernel is not coping well with that. But I still have to debug it further. Is there a reason for the zImage ELF header to request an interpreter and to have a virtual address of 0? -- []'s Thiago Jung Bauermann IBM Linux Technology Center