From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933124AbXFSCl6 (ORCPT ); Mon, 18 Jun 2007 22:41:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1763486AbXFSCls (ORCPT ); Mon, 18 Jun 2007 22:41:48 -0400 Received: from ms-smtp-01.nyroc.rr.com ([24.24.2.55]:64671 "EHLO ms-smtp-01.nyroc.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1763381AbXFSClr (ORCPT ); Mon, 18 Jun 2007 22:41:47 -0400 Subject: [PATCH RT] Don't call mcount from vsyscall_fn's From: Steven Rostedt To: Ingo Molnar Cc: Thomas Gleixner , LKML , RT Content-Type: text/plain Date: Mon, 18 Jun 2007 22:41:09 -0400 Message-Id: <1182220869.15228.10.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.6.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org This bit me in the butt. I couldn't understand why my init app was segfaulting, with a kernel address, but a user RIP and RSP. Well, the RIP I think was bogus, but the kernel address was always the start of "mcount". Looking deeper, I printed out what was in the RSP (even though it was a user stack). It ended up showing me that the calling address was from the VDSO area. Looking even further, I found the offending culprit, which was vread_hpet. Looking at the assembly dump, I saw the vread_hpet was calling mcount, but I could not see it in the code. Nor could I see it in hpet.i (-E option of compiling). Well, I guess Ingo is a magician when it comes to compiler tricks, and has the mcount being called by "every!!" function, unless you add the "notrace" option. This patch adds the notrace to vsyscall_fn, so that we don't have user land apps calling mcount and crashing! Signed-off-by: Steven Rostedt Index: linux-2.6-rt-test/include/asm-x86_64/vsyscall.h =================================================================== --- linux-2.6-rt-test.orig/include/asm-x86_64/vsyscall.h +++ linux-2.6-rt-test/include/asm-x86_64/vsyscall.h @@ -22,7 +22,7 @@ enum vsyscall_num { /* Definitions for CONFIG_GENERIC_TIME definitions */ #define __section_vsyscall_gtod_data __attribute__ \ ((unused, __section__ (".vsyscall_gtod_data"),aligned(16))) -#define __vsyscall_fn __attribute__ ((unused,__section__(".vsyscall_fn"))) +#define __vsyscall_fn __attribute__ ((unused,__section__(".vsyscall_fn"))) notrace #define VGETCPU_RDTSCP 1 #define VGETCPU_LSL 2