Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751872AbbBRNk4 (ORCPT ); Wed, 18 Feb 2015 08:40:56 -0500 Received: from smtp.codeaurora.org ([198.145.29.96]:36882 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750974AbbBRNkz (ORCPT ); Wed, 18 Feb 2015 08:40:55 -0500 Message-ID: <54E49663.6040706@codeaurora.org> Date: Wed, 18 Feb 2015 08:40:51 -0500 From: Christopher Covington User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:33.0) Gecko/20100101 Thunderbird/33.0 MIME-Version: 1.0 To: Catalin Marinas , Arnd Bergmann CC: Olof Johansson , Will Deacon , "agraf@suse.de" , "linux-arm-kernel@lists.infradead.org" , "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> <20141205110507.GB28339@e104818-lin.cambridge.arm.com> In-Reply-To: <20141205110507.GB28339@e104818-lin.cambridge.arm.com> 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 Content-Length: 2983 Lines: 68 On 12/05/2014 06:05 AM, Catalin Marinas wrote: > On Fri, Dec 05, 2014 at 10:39:40AM +0000, 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? > > The application doesn't even start because it cannot map page 0. It > looks like most 32-bit arm binaries are linked to be loaded at 32K. I looked at this briefly and the first problem I narrowed in on was underflow in the calculation of the off variable in elf_map(). http://lxr.free-electrons.com/source/fs/binfmt_elf.c?v=3.18#L341 Chris -- Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/