From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:39196 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935119AbdAFPJT (ORCPT ); Fri, 6 Jan 2017 10:09:19 -0500 Subject: Patch "ftrace/x86_32: Set ftrace_stub to weak to prevent gcc from using short jumps to it" has been added to the 4.9-stable tree To: rostedt@goodmis.org, colin.king@canonical.com, gregkh@linuxfoundation.org Cc: , From: Date: Fri, 06 Jan 2017 16:09:16 +0100 Message-ID: <148371535646177@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: This is a note to let you know that I've just added the patch titled ftrace/x86_32: Set ftrace_stub to weak to prevent gcc from using short jumps to it to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: ftrace-x86_32-set-ftrace_stub-to-weak-to-prevent-gcc-from-using-short-jumps-to-it.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >>From 847fa1a6d3d00f3bdf68ef5fa4a786f644a0dd67 Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (Red Hat)" Date: Thu, 8 Dec 2016 12:48:26 -0500 Subject: ftrace/x86_32: Set ftrace_stub to weak to prevent gcc from using short jumps to it 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) Patches currently in stable-queue which might be from rostedt@goodmis.org are queue-4.9/ftrace-x86_32-set-ftrace_stub-to-weak-to-prevent-gcc-from-using-short-jumps-to-it.patch queue-4.9/fgraph-handle-a-case-where-a-tracer-ignores-set_graph_notrace.patch