Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760230Ab1D1NoS (ORCPT ); Thu, 28 Apr 2011 09:44:18 -0400 Received: from mail-bw0-f46.google.com ([209.85.214.46]:46615 "EHLO mail-bw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759805Ab1D1NoQ convert rfc822-to-8bit (ORCPT ); Thu, 28 Apr 2011 09:44:16 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:sender:in-reply-to:references:date :x-google-sender-auth:message-id:subject:from:to:cc:content-type :content-transfer-encoding; b=k7nhZ8iUczXY2KpeJEOR9U1R4fWMyMimjuSdIyaCO+3owZrB02qqDzXNrVWLxRVFdM zCrZf0ct3jhJyO+BsH0SjlVFBvbrEF6DdTEvWFB6sgGzbRPtUu7igUHjHGBAQZkdya53 hbklZH2ZJRqT4+lih+F1odZZL78wtJnn6KcCk= MIME-Version: 1.0 In-Reply-To: <4DB98854020000780003EA4D@vpn.id2.novell.com> References: <4DB85404020000780003E6D7@vpn.id2.novell.com> <20110428104306.GC2431@osiris.boeblingen.de.ibm.com> <4DB96E6A020000780003E9EB@vpn.id2.novell.com> <4DB9748B020000780003EA01@vpn.id2.novell.com> <20110428125302.GD2431@osiris.boeblingen.de.ibm.com> <4DB98854020000780003EA4D@vpn.id2.novell.com> Date: Thu, 28 Apr 2011 15:44:13 +0200 X-Google-Sender-Auth: eKDSmDL2WtfwLB8PeD7cDTL6BOE Message-ID: Subject: Re: [PATCH] allow placing exception table in .rodata (and do so on x86) From: Geert Uytterhoeven To: Jan Beulich Cc: Heiko Carstens , mingo@elte.hu, tglx@linutronix.de, linux-arch@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, hpa@zytor.com Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2613 Lines: 53 On Thu, Apr 28, 2011 at 15:31, Jan Beulich wrote: >>>> On 28.04.11 at 14:53, Heiko Carstens wrote: >> On Thu, Apr 28, 2011 at 01:07:07PM +0100, Jan Beulich wrote: >>> >>> On 28.04.11 at 13:47, Geert Uytterhoeven wrote: >>> > On Thu, Apr 28, 2011 at 13:40, Jan Beulich wrote: >>> >>>>> On 28.04.11 at 12:43, Heiko Carstens wrote: >>> >>> On Wed, Apr 27, 2011 at 04:36:04PM +0100, Jan Beulich wrote: >>> >>> That's odd. The kernel actually writes to it (sort_main_extable()), so >>> >>> it shouldn't be in the ro data section, but the data section. >>> >> >>> >> This area does get written, but only at boot time, before read-only >>> >> data gets set to r/o (on x86 at least). With this in mind, it's better >>> >> to place it in .rodata, as that way run-time protection will be in place >>> >> (and I think you agree that it was misplaced in .text in any case). >>> > >>> > Which means it may be in ROM (which is really read-only) on some embedded >>> > devices, so it cannot be sorted? >>> >>> Perhaps - but since sorting is a requirement, people building such >>> systems must have found a way... Anyway, I don't see where both >> >> Yes, we found a way on s390: we put the exception table in the data section. >> >>> your and Heiko's comment are heading, since the situation is even >>> worse without the patch afaics (since .text gets marked read-only >>> as much as .rodata does, and could equally be placed in ROM). >> >> My point is that your default is wrong. If it makes sense to put the extable >> into the rodata section then an architecture could do so. However making the >> default to put data into the rodata section that is actually written to is >> the wrong approach. >> It just asks for breakage. > > The patch doesn't make this the default - it just makes it possible > for an architecture to do so. "asm-generic" is the default for new architectures. Gr{oetje,eeting}s,                         Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that.                                 -- Linus Torvalds -- 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/