Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754726AbbDNA0i (ORCPT ); Mon, 13 Apr 2015 20:26:38 -0400 Received: from blu004-omc4s22.hotmail.com ([65.55.111.161]:50576 "EHLO BLU004-OMC4S22.hotmail.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751951AbbDNA0g (ORCPT ); Mon, 13 Apr 2015 20:26:36 -0400 X-TMN: [pkKgYeE90gayzrKpPd5JpnFpPme7hVwG] X-Originating-Email: [minfei.huang@hotmail.com] Message-ID: Date: Tue, 14 Apr 2015 08:26:29 +0800 From: Minfei Huang To: Josh Poimboeuf CC: sjenning@redhat.com, jkosina@suse.cz, vojtech@suse.cz, live-patching@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] livepatch: Fix the bug if the function name is larger than KSYM_NAME_LEN-1 References: <1428844554-4015-1-git-send-email-minfei.huang@hotmail.com> <20150413231305.GD4412@treble.hsd1.ky.comcast.net> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20150413231305.GD4412@treble.hsd1.ky.comcast.net> User-Agent: Mutt/1.5.23 (2014-03-12) X-OriginalArrivalTime: 14 Apr 2015 00:26:35.0071 (UTC) FILETIME=[AA0244F0:01D07649] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3321 Lines: 79 On 04/13/15 at 06:13P, Josh Poimboeuf wrote: > On Sun, Apr 12, 2015 at 09:15:54PM +0800, Minfei Huang wrote: > > For now, the kallsyms will only store the first (KSYM_NAME_LEN-1). The > > kallsyms name is same for the function which first (KSYM_NAME_LEN-1) is > > same, but the rest is not. > > > > Then function will never be patched, although function name and address > > are provided both. The reason caused this bug is livepatch cannt > > recognize the function name. > > > > Now, livepatch will verify the function name with first (KSYM_NAME_LEN-1) > > and address, if provided. Once they are matched, we can confirm that the > > patched function is found. > > From scripts/kallsyms.c: > > if (strlen(str) > KSYM_NAME_LEN) { > fprintf(stderr, "Symbol %s too long for kallsyms (%zu vs %d).\n" > "Please increase KSYM_NAME_LEN both in kernel and kallsyms.c\n", > str, strlen(str), KSYM_NAME_LEN); > return -1; > } > > So I think such a long symbol name wouldn't be added to the kallsyms > database in the first place. > Actually, kernel allows overlength function name to be used. Following is my testing module. We can got the address in /proc/kallsyms. $ cat /proc/kallsyms | grep sysfs_print ffffffffa0000000 t sys_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_pri [sysfs_print] ffffffffa0000010 t kobj_release [sysfs_print] ffffffffa0000020 t sys_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_pri [sysfs_print] ffffffffa00004e0 b root_kobj [sysfs_print] ffffffffa0000200 d print_ktype [sysfs_print] ffffffffa00004a0 b print_kobj [sysfs_print] ffffffffa000004c t sys_print_exit [sysfs_print] ffffffffa0000144 r __func__.14514 [sysfs_print] ffffffffa0000230 d kobj_attrs [sysfs_print] ffffffffa0000240 d sys_print_kobj_attr [sysfs_print] ffffffffa0000260 d __this_module [sysfs_print] ffffffffa000004c t cleanup_module [sysfs_print] Code: static ssize_t sys_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_store(struct kobject *kobj, s const char *buf, size_t count) { return count; } static ssize_t sys_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_show(struct kobject *kobj, struct kobj_attribute *attr, char *buf) { return snprintf(buf, PAGE_SIZE-1, "%s\n", "This is printed by module"); } static struct kobj_attribute sys_print_kobj_attr = __ATTR_RW(sys_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_print_p static struct attribute *kobj_attrs[] = { &sys_print_kobj_attr.attr, NULL }; Thanks Minfei > -- > Josh > -- > To unsubscribe from this list: send the line "unsubscribe live-patching" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/