Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752432AbaLELFW (ORCPT ); Fri, 5 Dec 2014 06:05:22 -0500 Received: from foss-mx-na.foss.arm.com ([217.140.108.86]:45125 "EHLO foss-mx-na.foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751723AbaLELFS (ORCPT ); Fri, 5 Dec 2014 06:05:18 -0500 Date: Fri, 5 Dec 2014 11:05:07 +0000 From: Catalin Marinas To: Arnd Bergmann Cc: "linux-arm-kernel@lists.infradead.org" , Olof Johansson , "agraf@suse.de" , Will Deacon , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] arm64: Enable CONFIG_COMPAT also for 64k page size Message-ID: <20141205110507.GB28339@e104818-lin.cambridge.arm.com> References: <1417707993-82290-1-git-send-email-agraf@suse.de> <5480F12D.90007@suse.de> <3551792.oHatG1W6W1@wuerfel> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3551792.oHatG1W6W1@wuerfel> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > Should we add support for 64k-pages in the arm32 kernel as well now? 32-bit LPAE doesn't support 64K pages but IIRC the classic MMU does (though I have to check whether it was optional). But it's not feasible to enable this in a 32-bit environment because of the memory wasted with large pages (on average 32KB per mapped file, possibly even more if you have lots of small files). -- Catalin -- 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/