From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753567Ab2HTLAx (ORCPT ); Mon, 20 Aug 2012 07:00:53 -0400 Received: from nat28.tlf.novell.com ([130.57.49.28]:33196 "EHLO nat28.tlf.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753266Ab2HTLAt convert rfc822-to-8bit (ORCPT ); Mon, 20 Aug 2012 07:00:49 -0400 Message-Id: <503234FC0200007800096611@nat28.tlf.novell.com> X-Mailer: Novell GroupWise Internet Agent 12.0.0 Date: Mon, 20 Aug 2012 12:00:44 +0100 From: "Jan Beulich" To: "Andi Kleen" Cc: , , , , , Subject: Re: [PATCH 55/74] lto, workaround: Add workaround for initcall reordering References: <1345345030-22211-1-git-send-email-andi@firstfloor.org> <1345345030-22211-56-git-send-email-andi@firstfloor.org> <5030B5DC020000780008A226@nat28.tlf.novell.com> <20120819150140.GP11413@one.firstfloor.org> In-Reply-To: <20120819150140.GP11413@one.firstfloor.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >>> On 19.08.12 at 17:01, Andi Kleen wrote: > On Sun, Aug 19, 2012 at 09:46:04AM +0100, Jan Beulich wrote: >> >>> Andi Kleen 08/19/12 5:05 AM >>> >> >Work around a LTO gcc problem: when there is no reference to a variable >> >in a module it will be moved to the end of the program. This causes >> >reordering of initcalls which the kernel does not like. >> >Add a dummy reference function to avoid this. The function is >> >deleted by the linker. >> >> This is not even true on x86, not to speak of generally. > > Why is it not true ? > > __initcall is only defined for !MODULE and there __exit discards. __exit, on x86 and perhaps other arches, causes the code to be discarded at runtime only. >> >+#ifdef CONFIG_LTO >> >+/* Work around a LTO gcc problem: when there is no reference to a variable >> >+ * in a module it will be moved to the end of the program. This causes >> >+ * reordering of initcalls which the kernel does not like. >> >+ * Add a dummy reference function to avoid this. The function is >> >+ * deleted by the linker. >> >+ */ >> >+#define LTO_REFERENCE_INITCALL(x) \ >> >+ ; /* yes this is needed */ \ >> >+ static __used __exit void *reference_##x(void) \ >> >> Why not put it into e.g. section .discard.text? That could be expected to be >> discarded by the linker without being arch dependent, as long as all arches >> use DISCARDS in their linker script. > > > That's what __exit does, doesn't it? No - see above. Using .discard.* enforces the discarding at link time. Jan