Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755269Ab0KXAEM (ORCPT ); Tue, 23 Nov 2010 19:04:12 -0500 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:42101 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753622Ab0KXAEL (ORCPT ); Tue, 23 Nov 2010 19:04:11 -0500 X-Authority-Analysis: v=1.1 cv=NFUeGz0loTdi/T6hXKngYYtckjed7x3pKvNOqmBBK18= c=1 sm=0 a=fIAfbhESzNEA:10 a=Q9fys5e9bTEA:10 a=OPBmh+XkhLl+Enan7BmTLg==:17 a=20KFwNOVAAAA:8 a=6YOI96l4G83usf4b_DAA:9 a=GZVc01_FfxH0Qz1qQJIA:7 a=J_3dA8Ufw0C3biMEjoqgfPWWGDwA:4 a=PUjeQqilurYA:10 a=jEp0ucaQiEUA:10 a=OPBmh+XkhLl+Enan7BmTLg==:117 X-Cloudmark-Score: 0 X-Originating-IP: 67.242.120.143 Subject: Re: [PATCH 2/3] jump label: move jump table to r/w section From: Steven Rostedt To: Mathieu Desnoyers Cc: Jason Baron , 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 In-Reply-To: <20101123235519.GB21549@Krystal> References: <20101123235519.GB21549@Krystal> Content-Type: text/plain; charset="ISO-8859-15" Date: Tue, 23 Nov 2010 19:04:09 -0500 Message-ID: <1290557049.30543.417.camel@gandalf.stny.rr.com> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2319 Lines: 61 On Tue, 2010-11-23 at 18:55 -0500, Mathieu Desnoyers wrote: > * 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. Agreed, but this change could probably wait for 2.6.38. Also, if this is done, then an it should be wrapped in a #ifdef CONFIG_JUMP_LABEL and only inserted if we are using jump labels. Otherwise we may add a 32 byte hole for nothing. I know it's small, but why waste it if you don't need to. -- Steve -- 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/