Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754949AbaLDXs5 (ORCPT ); Thu, 4 Dec 2014 18:48:57 -0500 Received: from mail-vc0-f172.google.com ([209.85.220.172]:39801 "EHLO mail-vc0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754730AbaLDXsz (ORCPT ); Thu, 4 Dec 2014 18:48:55 -0500 MIME-Version: 1.0 X-Originating-IP: [2620:0:1000:157d:18e4:f2cc:a02b:2d5c] In-Reply-To: <5480F12D.90007@suse.de> References: <1417707993-82290-1-git-send-email-agraf@suse.de> <5480F12D.90007@suse.de> Date: Thu, 4 Dec 2014 15:48:50 -0800 Message-ID: Subject: Re: [PATCH] arm64: Enable CONFIG_COMPAT also for 64k page size From: Olof Johansson To: Alexander Graf Cc: "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , Will Deacon , Catalin Marinas Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. >> So, it seems very premature to take this off. At the very least >> document it like Will requested, and make it depend on !ARM_64K_PAGES >> || EXPERT. > > Sure, that certainly works for me (though you probably mean Laura). Yeah, sorry Laura. :) > Completely restricting users from enabling it just because our current > toolchain doesn't generate compatible binaries sounds a bit extreme to me. Perhaps. It's in many ways a timing thing too, if ARM had patched binutils a couple of years ago it might have been fine to just go with it without EXPERT now. :) -Olof -- 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/