Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757529AbcCURgn (ORCPT ); Mon, 21 Mar 2016 13:36:43 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48268 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757145AbcCURgl (ORCPT ); Mon, 21 Mar 2016 13:36:41 -0400 Date: Mon, 21 Mar 2016 12:36:39 -0500 From: Josh Poimboeuf To: Petr Mladek Cc: Jessica Yu , Rusty Russell , Jiri Kosina , Jonathan Corbet , Miroslav Benes , linux-api@vger.kernel.org, live-patching@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, linux-doc@vger.kernel.org Subject: Re: [PATCH v5 4/6] livepatch: reuse module loader code to write relocations Message-ID: <20160321173639.ooighgwwubuqv6le@treble.redhat.com> References: <1458157628-8264-1-git-send-email-jeyu@redhat.com> <1458157628-8264-5-git-send-email-jeyu@redhat.com> <20160321163157.GG19401@pathway.suse.cz> <20160321164651.zautqklg7ng3jfbn@treble.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20160321164651.zautqklg7ng3jfbn@treble.redhat.com> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1985 Lines: 55 On Mon, Mar 21, 2016 at 11:46:51AM -0500, Josh Poimboeuf wrote: > On Mon, Mar 21, 2016 at 05:31:57PM +0100, Petr Mladek wrote: > > > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c > > > index 780f00c..2aa20fa 100644 > > > --- a/kernel/livepatch/core.c > > > +++ b/kernel/livepatch/core.c > > > +static int klp_resolve_symbols(Elf_Shdr *relasec, struct module *pmod) > > > +{ > > > + int i, cnt, vmlinux, ret; > > > + struct klp_buf bufs = {0}; > > > + Elf_Rela *relas; > > > + Elf_Sym *sym; > > > + char *symname; > > > + unsigned long sympos; > > > + > > > + relas = (Elf_Rela *) relasec->sh_addr; > > > + /* For each rela in this klp relocation section */ > > > + for (i = 0; i < relasec->sh_size / sizeof(Elf_Rela); i++) { > > > + sym = pmod->core_kallsyms.symtab + ELF_R_SYM(relas[i].r_info); > > > + if (sym->st_shndx != SHN_LIVEPATCH) > > > + return -EINVAL; > > > + > > > + klp_clear_buf(&bufs); > > > + > > > + /* Format: .klp.sym.objname.symbol_name,sympos */ > > > + symname = pmod->core_kallsyms.strtab + sym->st_name; > > > + cnt = sscanf(symname, ".klp.sym.%64[^.].%128[^,],%lu", > > > + bufs.objname, bufs.symname, &sympos); > > > > Note that MODULE_NAME_LEN even is not 64. It is defined by: > > > > #define MAX_PARAM_PREFIX_LEN (64 - sizeof(unsigned long)) > > > > I strongly suggest to use the proposal from Josh. > > Hm, looks like my suggestion to use __stringify(MODULE_NAME_LEN) doesn't > work. It results in the string "MODULE_NAME_LEN". Which surprises me: > isn't is supposed to resolve the macro before applying the '#' operation > to it? Turns out I hadn't included module.h. When I do so, __stringify(MODULE_NAME_LEN) becomes "(64 - sizeof(unsigned long))". Which is still not going to work :-/ > I was going to suggest another idea: hard-code it at 63 and then do > something like > > BUILD_BUG_ON(MODULE_NAME_LEN != 64) > > But you're right... it's not even 64! > > Need to think on this some more... -- Josh