From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751978AbdB0WKW (ORCPT ); Mon, 27 Feb 2017 17:10:22 -0500 Received: from mail.kernel.org ([198.145.29.136]:54038 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751620AbdB0WKS (ORCPT ); Mon, 27 Feb 2017 17:10:18 -0500 Date: Mon, 27 Feb 2017 17:09:11 -0500 From: Steven Rostedt To: David Daney Cc: Jason Baron , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mips@linux-mips.org, linuxppc-dev@lists.ozlabs.org, Ingo Molnar , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Anton Blanchard , Rabin Vincent , Russell King , Ralf Baechle , Chris Metcalf , Zhigang Lu Subject: Re: [PATCH] jump_label: align jump_entry table to at least 4-bytes Message-ID: <20170227170911.2280ca3e@gandalf.local.home> In-Reply-To: <6db89a8d-6053-51d1-5fd4-bae0179a5ebd@caviumnetworks.com> References: <1488221364-13905-1-git-send-email-jbaron@akamai.com> <93219edf-0f6d-5cc7-309c-c998f16fe7ac@akamai.com> <20170227160601.5b79a1fe@gandalf.local.home> <6db89a8d-6053-51d1-5fd4-bae0179a5ebd@caviumnetworks.com> X-Mailer: Claws Mail 3.14.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 27 Feb 2017 13:41:13 -0800 David Daney wrote: > On 02/27/2017 01:06 PM, Steven Rostedt wrote: > > On Mon, 27 Feb 2017 11:59:50 -0800 > > David Daney wrote: > > > >> For me the size is not the important issue, it is the alignment of the > >> struct jump_entry entries in the table. I don't understand how your > >> patch helps, and I cannot Acked-by unless I understand what is being > >> done and can see that it is both correct and necessary. > > > > You brought up a very good point and I'm glad that I had Jason Cc all > > the arch maintainers in one patch. > > > > I think jump_labels may be much more broken than we think, and Jason's > > fix doesn't fix anything. We had this same issues with tracepoints. > > > > I'm looking at jump_label_init, and how we iterate over an array of > > struct jump_entry's that was put together by the linker. The problem is > > that jump_entry is not a power of 2 in size. > > > > ELF sections may have an ENTSIZE property exactly for arrays. Since > each jump_entry will have a unique value they cannot be merged, but we > can tell the assembler they are an array and get them properly packed. > Perhaps something like (untested): > > .pushsection __jump_table, \"awM\",@progbits,24 > FOO > .popsection > And the linker will honor this too? -- Steve From mboxrd@z Thu Jan 1 00:00:00 1970 From: rostedt@goodmis.org (Steven Rostedt) Date: Mon, 27 Feb 2017 17:09:11 -0500 Subject: [PATCH] jump_label: align jump_entry table to at least 4-bytes In-Reply-To: <6db89a8d-6053-51d1-5fd4-bae0179a5ebd@caviumnetworks.com> References: <1488221364-13905-1-git-send-email-jbaron@akamai.com> <93219edf-0f6d-5cc7-309c-c998f16fe7ac@akamai.com> <20170227160601.5b79a1fe@gandalf.local.home> <6db89a8d-6053-51d1-5fd4-bae0179a5ebd@caviumnetworks.com> Message-ID: <20170227170911.2280ca3e@gandalf.local.home> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, 27 Feb 2017 13:41:13 -0800 David Daney wrote: > On 02/27/2017 01:06 PM, Steven Rostedt wrote: > > On Mon, 27 Feb 2017 11:59:50 -0800 > > David Daney wrote: > > > >> For me the size is not the important issue, it is the alignment of the > >> struct jump_entry entries in the table. I don't understand how your > >> patch helps, and I cannot Acked-by unless I understand what is being > >> done and can see that it is both correct and necessary. > > > > You brought up a very good point and I'm glad that I had Jason Cc all > > the arch maintainers in one patch. > > > > I think jump_labels may be much more broken than we think, and Jason's > > fix doesn't fix anything. We had this same issues with tracepoints. > > > > I'm looking at jump_label_init, and how we iterate over an array of > > struct jump_entry's that was put together by the linker. The problem is > > that jump_entry is not a power of 2 in size. > > > > ELF sections may have an ENTSIZE property exactly for arrays. Since > each jump_entry will have a unique value they cannot be merged, but we > can tell the assembler they are an array and get them properly packed. > Perhaps something like (untested): > > .pushsection __jump_table, \"awM\", at progbits,24 > FOO > .popsection > And the linker will honor this too? -- Steve