From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752085AbaLEMGO (ORCPT ); Fri, 5 Dec 2014 07:06:14 -0500 Received: from cantor2.suse.de ([195.135.220.15]:42748 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750969AbaLEMGM (ORCPT ); Fri, 5 Dec 2014 07:06:12 -0500 Message-ID: <54819FB2.6000408@suse.de> Date: Fri, 05 Dec 2014 13:06:10 +0100 From: Alexander Graf User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:31.0) Gecko/20100101 Thunderbird/31.3.0 MIME-Version: 1.0 To: Arnd Bergmann , linux-arm-kernel@lists.infradead.org CC: Olof Johansson , Catalin Marinas , Will Deacon , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] arm64: Enable CONFIG_COMPAT also for 64k page size References: <1417707993-82290-1-git-send-email-agraf@suse.de> <5480F12D.90007@suse.de> <3551792.oHatG1W6W1@wuerfel> In-Reply-To: <3551792.oHatG1W6W1@wuerfel> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 05.12.14 11:39, Arnd Bergmann wrote: > On Thursday 04 December 2014 15:48:50 Olof Johansson wrote: >> On Thu, Dec 4, 2014 at 3:41 PM, Alexander Graf wrote: >>> On 04.12.14 22:15, Olof Johansson wrote: >>>> On Thu, Dec 4, 2014 at 7:46 AM, Alexander Graf wrote: >>>>> With binutils 2.25 the default alignment for 32bit arm sections changed to >>>>> have everything 64k aligned. Armv7 binaries built with this binutils version >>>>> run successfully on an arm64 system. >>>>> >>>>> Since effectively there is now the chance to run armv7 code on arm64 even >>>>> with 64k page size, it doesn't make sense to block people from enabling >>>>> CONFIG_COMPAT on those configurations. >>>>> >>>>> Signed-off-by: Alexander Graf >>>>> --- >>>>> arch/arm64/Kconfig | 1 - >>>>> 1 file changed, 1 deletion(-) >>>>> >>>>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig >>>>> index 9532f8d..3cf4f238 100644 >>>>> --- a/arch/arm64/Kconfig >>>>> +++ b/arch/arm64/Kconfig >>>>> @@ -409,7 +409,6 @@ source "fs/Kconfig.binfmt" >>>>> >>>>> config COMPAT >>>>> bool "Kernel support for 32-bit EL0" >>>>> - depends on !ARM64_64K_PAGES >>>>> select COMPAT_BINFMT_ELF >>>>> select HAVE_UID16 >>>>> select OLD_SIGSUSPEND3 >>>> >>>> This is hardly "compat". Sure, it's great to have a new binutils that >>>> has larger alignment, but practically not a single existing binary >>>> will work today if someone tries to do this. >>> >>> Yes, but IMHO that's an implementation detail. The same applies for >>> 32bit PPC binaries if you use 4k aligned segments. If your applications >>> are not aligned for your page size, you can't run them. The only >>> platform that managed nevertheless FWIW was IA64 ;). >> >> Yes, but there the binutils change happened early enough that by the >> time the kernel change went in, all major distros had binaries that >> were compatible. > > What is the exact symptom you see when running an unaligned user > space binary on 64k-pages? Do we at least print a helpful error > message somewhere or does it just crash? It simply doesn't start: init-4.2# /hello.binutils-2.23 init-4.2# echo $? 139 init-4.2# /hello.binutils-2.25 Hello world! init-4.2# echo $? 0 init-4.2# I'm not sure how to give the user an actually helpful error output here though. The only real handle we have for executing a binary is to return an error code. Alex