Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756221Ab0KXAk0 (ORCPT ); Tue, 23 Nov 2010 19:40:26 -0500 Received: from tomts13.bellnexxia.net ([209.226.175.34]:50569 "EHLO tomts13-srv.bellnexxia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754410Ab0KXAkZ (ORCPT ); Tue, 23 Nov 2010 19:40:25 -0500 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AvsEAJbn60xGHlyW/2dsb2JhbACianK+EIVLBIRaOA Date: Tue, 23 Nov 2010 18:55:19 -0500 From: Mathieu Desnoyers To: Jason Baron Cc: rostedt@goodmis.org, mingo@elte.hu, peterz@infradead.org, hpa@zytor.com, tglx@linutronix.de, andi@firstfloor.org, roland@redhat.com, rth@redhat.com, masami.hiramatsu.pt@hitachi.com, fweisbec@gmail.com, avi@redhat.com, davem@davemloft.net, sam@ravnborg.org, ddaney@caviumnetworks.com, michael@ellerman.id.au, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/3] jump label: move jump table to r/w section Message-ID: <20101123235519.GB21549@Krystal> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.6.27.31-grsec (i686) X-Uptime: 18:49:00 up 230 days, 9:39, 4 users, load average: 0.01, 0.05, 0.07 User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1987 Lines: 59 * Jason Baron (jbaron@redhat.com) wrote: > Since we writing the jump table it should be be in R/W kernel > section. Move it to DATA_DATA > > Signed-off-by: Jason Baron > --- > include/asm-generic/vmlinux.lds.h | 14 ++++---------- > 1 files changed, 4 insertions(+), 10 deletions(-) > > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h > index bd69d79..9ca894d 100644 > --- a/include/asm-generic/vmlinux.lds.h > +++ b/include/asm-generic/vmlinux.lds.h > @@ -161,6 +161,10 @@ > VMLINUX_SYMBOL(__start___tracepoints) = .; \ > *(__tracepoints) \ > VMLINUX_SYMBOL(__stop___tracepoints) = .; \ > + . = ALIGN(8); \ Past churn with various architectures and compiler with tracepoints, markers and immediate values lead me to hint at the following approach for jump label structure alignment: . = ALIGN(32); and to modify jump_label.h to have: struct jump_entry { jump_label_t code; jump_label_t target; jump_label_t key; } __attribute__((aligned(32))); Otherwise, the compiler is free to choose on which value it prefers to align the jump_entry structures, which might not match the address at which the linker scripts puts the beginning of the jump table. In this case, given that we put put the jump label table after the tracepoint table, we should be already aligned on 32 bytes. But I would recommend to put the . = ALIGN(32) in the linker script anyway, just for documentation purpose (and it should not add any padding in this case). This is not a problem introduced by this patch, it also applies to the current jump label code. Thanks, Mathieu -- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com -- 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/