From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1033778AbdAFWEl (ORCPT ); Fri, 6 Jan 2017 17:04:41 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:55610 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S968722AbdAFWAJ (ORCPT ); Fri, 6 Jan 2017 17:00:09 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Colin Ian King , Steven Rostedt Subject: [PATCH 4.9 077/116] ftrace/x86_32: Set ftrace_stub to weak to prevent gcc from using short jumps to it Date: Fri, 6 Jan 2017 22:43:59 +0100 Message-Id: <20170106213912.262448256@linuxfoundation.org> X-Mailer: git-send-email 2.11.0 In-Reply-To: <20170106213908.681421800@linuxfoundation.org> References: <20170106213908.681421800@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Steven Rostedt (Red Hat) commit 847fa1a6d3d00f3bdf68ef5fa4a786f644a0dd67 upstream. With new binutils, gcc may get smart with its optimization and change a jmp from a 5 byte jump to a 2 byte one even though it was jumping to a global function. But that global function existed within a 2 byte radius, and gcc was able to optimize it. Unfortunately, that jump was also being modified when function graph tracing begins. Since ftrace expected that jump to be 5 bytes, but it was only two, it overwrote code after the jump, causing a crash. This was fixed for x86_64 with commit 8329e818f149, with the same subject as this commit, but nothing was done for x86_32. Fixes: d61f82d06672 ("ftrace: use dynamic patching for updating mcount calls") Reported-by: Colin Ian King Tested-by: Colin Ian King Signed-off-by: Steven Rostedt Signed-off-by: Greg Kroah-Hartman --- arch/x86/entry/entry_32.S | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -889,8 +889,8 @@ ftrace_graph_call: jmp ftrace_stub #endif -.globl ftrace_stub -ftrace_stub: +/* This is weak to keep gas from relaxing the jumps */ +WEAK(ftrace_stub) ret END(ftrace_caller)