From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:50820 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752050AbcDQLBh (ORCPT ); Sun, 17 Apr 2016 07:01:37 -0400 Subject: Patch "ARM: 8550/1: protect idiv patching against undefined gcc behavior" has been added to the 4.5-stable tree To: nicolas.pitre@linaro.org, arnd@arndb.de, gregkh@linuxfoundation.org, mjuszkiewicz@redhat.com, nico@linaro.org, rmk+kernel@arm.linux.org.uk Cc: , From: Date: Sun, 17 Apr 2016 03:26:30 -0700 Message-ID: <146088879056117@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 ARM: 8550/1: protect idiv patching against undefined gcc behavior to the 4.5-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: arm-8550-1-protect-idiv-patching-against-undefined-gcc-behavior.patch and it can be found in the queue-4.5 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >>From 208fae5c3b9431013ad7bcea07cbcee114e7d163 Mon Sep 17 00:00:00 2001 From: Nicolas Pitre Date: Mon, 14 Mar 2016 02:55:45 +0100 Subject: ARM: 8550/1: protect idiv patching against undefined gcc behavior From: Nicolas Pitre commit 208fae5c3b9431013ad7bcea07cbcee114e7d163 upstream. It was reported that a kernel with CONFIG_ARM_PATCH_IDIV=y stopped booting when compiled with the upcoming gcc 6. Turns out that turning a function address into a writable array is undefined and gcc 6 decided it was OK to omit the store to the first word of the function while still preserving the store to the second word. Even though gcc 6 is now fixed to behave more coherently, it is a mystery that gcc 4 and gcc 5 actually produce wanted code in the kernel. And in fact the reduced test case to illustrate the issue does indeed break with gcc < 6 as well. In any case, let's guard the kernel against undefined compiler behavior by hiding the nature of the array location as suggested by gcc developers. Reference: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70128 Signed-off-by: Nicolas Pitre Reported-by: Marcin Juszkiewicz Cc: Arnd Bergmann Signed-off-by: Russell King Signed-off-by: Greg Kroah-Hartman --- arch/arm/kernel/setup.c | 2 ++ 1 file changed, 2 insertions(+) --- a/arch/arm/kernel/setup.c +++ b/arch/arm/kernel/setup.c @@ -430,11 +430,13 @@ static void __init patch_aeabi_idiv(void pr_info("CPU: div instructions available: patching division code\n"); fn_addr = ((uintptr_t)&__aeabi_uidiv) & ~1; + asm ("" : "+g" (fn_addr)); ((u32 *)fn_addr)[0] = udiv_instruction(); ((u32 *)fn_addr)[1] = bx_lr_instruction(); flush_icache_range(fn_addr, fn_addr + 8); fn_addr = ((uintptr_t)&__aeabi_idiv) & ~1; + asm ("" : "+g" (fn_addr)); ((u32 *)fn_addr)[0] = sdiv_instruction(); ((u32 *)fn_addr)[1] = bx_lr_instruction(); flush_icache_range(fn_addr, fn_addr + 8); Patches currently in stable-queue which might be from nicolas.pitre@linaro.org are queue-4.5/arm-8550-1-protect-idiv-patching-against-undefined-gcc-behavior.patch