From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753195AbbAEE3R (ORCPT ); Sun, 4 Jan 2015 23:29:17 -0500 Received: from ozlabs.org ([103.22.144.67]:54733 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753169AbbAEE3Q (ORCPT ); Sun, 4 Jan 2015 23:29:16 -0500 From: Rusty Russell To: Oded Gabbay , Andi Kleen , Alex Deucher , Kees Cook , "H. Peter Anvin" Cc: Dana Elifaz , LKML , Maling list - DRI developers , Alexander Deucher , LKP ML Subject: Re: [LKP] [PATCH] drm/radeon: Try to init amdkfd only if 64 bit kernel In-Reply-To: <549A85DE.1040006@amd.com> References: <1419246673-7222-1-git-send-email-oded.gabbay@amd.com> <20141222184940.GB17192@tassilo.jf.intel.com> <20141222190041.GC17192@tassilo.jf.intel.com> <54986EA2.106@amd.com> <874msmt1hi.fsf@rustcorp.com.au> <549A85DE.1040006@amd.com> User-Agent: Notmuch/0.17 (http://notmuchmail.org) Emacs/24.3.1 (x86_64-pc-linux-gnu) Date: Mon, 05 Jan 2015 14:58:54 +1030 Message-ID: <87r3v96ebd.fsf@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Oded Gabbay writes: > On 12/24/2014 01:01 AM, Rusty Russell wrote: >> Oded Gabbay writes: >>> I didn't say it doesn't always work. >>> The actual thing that doesn't work is the define symbol_get and only in a >>> specific case of 32bit kernel AND CONFIG_MODULES is unset AND >>> CONFIG_RANDOMIZE_BASE is set. >>> The define in that case is: >>> #define symbol_get(x) ({ extern typeof(x) x __attribute__((weak)); &(x); }) >>> >>> Why it doesn't work (doesn't return NULL when symbol doesn't exists) ? >> >> Hmm, I'd guess CONFIG_RANDOMIZE_BASE is relocating NULL symbols... >> >> No, I can't reproduce this. Please send your .config privately. >> >> Here's my test case: >> >> diff --git a/init/main.c b/init/main.c >> index 61b993767db5..a3ee1ec97ec3 100644 >> --- a/init/main.c >> +++ b/init/main.c >> @@ -683,6 +683,12 @@ asmlinkage __visible void __init start_kernel(void) >> >> ftrace_init(); >> >> + { >> + extern void nonexistent_fn(void); >> + printk("symbol_get(nonexistent_fn) = %p\n", >> + symbol_get(nonexistent_fn)); >> + } >> + >> /* Do the rest non-__init'ed, we're now alive */ >> rest_init(); >> } >> >> Thanks, >> Rusty. >> > Hi Rusty, > > Attached is the bad config file. (config-bad) > I have narrowed the changes you need to do to the config file in order to > reproduce this bug. > The base assumption is a 32-bit kernel and without modules support. Rest of the > config file is pretty standard, IMO. > Then, its not enough to enable CONFIG_RANDOMIZE_BASE like I wrote in my original > post. You need also to unset CONFIG_HIBERNATION. Indeed, thanks; your config breaks as reported. With CONFIG_HIBERNATION the kernel offset is 0, so we don't see this. Kees, as far as I can tell you need another 0-terminated vmlinux.relocs section for weak symbols. These should not be relocated if already 0. Put this somewhere to test. It fails for x86_64, too: diff --git a/init/main.c b/init/main.c index 61b993767db5..c9e0195c792a 100644 --- a/init/main.c +++ b/init/main.c @@ -683,6 +683,12 @@ asmlinkage __visible void __init start_kernel(void) ftrace_init(); + { + extern void __attribute__((weak)) nonexistent_fn(void); + printk("nonexistent_fn = %p\n", nonexistent_fn); + BUG_ON(nonexistent_fn != NULL); + } + /* Do the rest non-__init'ed, we're now alive */ rest_init(); } Cheers, Rusty.