From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:41610 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752271AbdATPDd (ORCPT ); Fri, 20 Jan 2017 10:03:33 -0500 Subject: Patch "ftrace/x86: Set ftrace_stub to weak to prevent gcc from using short jumps to it" has been added to the 4.4-stable tree To: rostedt@goodmis.org, gregkh@linuxfoundation.org, hjl.tools@gmail.com, jslaby@suse.cz, matt@codeblueprint.co.uk, mhiramat@kernel.org, namhyung@kernel.org Cc: , From: Date: Fri, 20 Jan 2017 15:53:07 +0100 Message-ID: <14849239872493@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: Set ftrace_stub to weak to prevent gcc from using short jumps to it to the 4.4-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-set-ftrace_stub-to-weak-to-prevent-gcc-from-using-short-jumps-to-it.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >>From 8329e818f14926a6040df86b2668568bde342ebf Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Mon, 16 May 2016 23:00:35 -0400 Subject: ftrace/x86: Set ftrace_stub to weak to prevent gcc from using short jumps to it From: Steven Rostedt commit 8329e818f14926a6040df86b2668568bde342ebf upstream. Matt Fleming reported seeing crashes when enabling and disabling function profiling which uses function graph tracer. Later Namhyung Kim hit a similar issue and he found that the issue was due to the jmp to ftrace_stub in ftrace_graph_call was only two bytes, and when it was changed to jump to the tracing code, it overwrote the ftrace_stub that was after it. Masami Hiramatsu bisected this down to a binutils change: 8dcea93252a9ea7dff57e85220a719e2a5e8ab41 is the first bad commit commit 8dcea93252a9ea7dff57e85220a719e2a5e8ab41 Author: H.J. Lu Date: Fri May 15 03:17:31 2015 -0700 Add -mshared option to x86 ELF assembler This patch adds -mshared option to x86 ELF assembler. By default, assembler will optimize out non-PLT relocations against defined non-weak global branch targets with default visibility. The -mshared option tells the assembler to generate code which may go into a shared library where all non-weak global branch targets with default visibility can be preempted. The resulting code is slightly bigger. This option only affects the handling of branch instructions. Declaring ftrace_stub as a weak call prevents gas from using two byte jumps to it, which would be converted to a jump to the function graph code. Link: http://lkml.kernel.org/r/20160516230035.1dbae571@gandalf.local.home Reported-by: Matt Fleming Reported-by: Namhyung Kim Tested-by: Matt Fleming Reviewed-by: Masami Hiramatsu Signed-off-by: Steven Rostedt Cc: Jiri Slaby Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/mcount_64.S | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/arch/x86/kernel/mcount_64.S +++ b/arch/x86/kernel/mcount_64.S @@ -180,7 +180,8 @@ GLOBAL(ftrace_graph_call) jmp ftrace_stub #endif -GLOBAL(ftrace_stub) +/* This is weak to keep gas from relaxing the jumps */ +WEAK(ftrace_stub) retq END(ftrace_caller) Patches currently in stable-queue which might be from rostedt@goodmis.org are queue-4.4/ftrace-x86-set-ftrace_stub-to-weak-to-prevent-gcc-from-using-short-jumps-to-it.patch