From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S979679AbdDYBYf (ORCPT ); Mon, 24 Apr 2017 21:24:35 -0400 Received: from host.buserror.net ([209.198.135.123]:42721 "EHLO host.buserror.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S938672AbdDYBYZ (ORCPT ); Mon, 24 Apr 2017 21:24:25 -0400 Date: Mon, 24 Apr 2017 20:24:13 -0500 From: Scott Wood To: Liu Hailong Cc: benh@kernel.crashing.org, zhong.weidong@zte.com.cn, linux-kernel@vger.kernel.org, liu.song11@zte.com.cn, huang.jian@zte.com.cn, jiang.xuexin@zte.com.cn, jiang.biao2@zte.com.cn, linuxppc-dev@lists.ozlabs.org Message-ID: <20170425012413.gaobi3atq7noa5v7@home.buserror.net> References: <1486434952-2093-1-git-send-email-liu.hailong6@zte.com.cn> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1486434952-2093-1-git-send-email-liu.hailong6@zte.com.cn> User-Agent: NeoMutt/20170113 (1.7.2) X-SA-Exim-Connect-IP: 50.171.225.118 X-SA-Exim-Rcpt-To: liu.hailong6@zte.com.cn, benh@kernel.crashing.org, zhong.weidong@zte.com.cn, linux-kernel@vger.kernel.org, liu.song11@zte.com.cn, huang.jian@zte.com.cn, jiang.xuexin@zte.com.cn, jiang.biao2@zte.com.cn, linuxppc-dev@lists.ozlabs.org X-SA-Exim-Mail-From: oss@buserror.net X-Spam-Report: * -1.0 ALL_TRUSTED Passed through trusted hosts only via SMTP * -15 BAYES_00 BODY: Bayes spam probability is 0 to 1% * [score: 0.0000] * 0.0 URIBL_BLOCKED ADMINISTRATOR NOTICE: The query to URIBL was blocked. * See http://wiki.apache.org/spamassassin/DnsBlocklists#dnsbl-block * for more information. * [URIs: zte.com.cn] * -1.5 GREYLIST_ISWHITE The incoming server has been whitelisted for this * recipient and sender Subject: Re: Powerpc64: Fixup oops when debug programs with CONFIG_RELOCATABLE=y X-SA-Exim-Version: 4.2.1 (built Mon, 26 Dec 2011 16:57:07 +0000) X-SA-Exim-Scanned: Yes (on host.buserror.net) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 07, 2017 at 10:35:52AM +0800, Liu Hailong wrote: > From: LiuHailong > > Debug interrupts can be taken during regular program or a standard > interrupt, the EA of the instruction causing the interrupt will be > kept in DSRR0. > Kernel will check if this value is between [interrupt_base_book3e, > __end_interrupts]. > However, when the kernel build with CONFIG_RELOCATABLE, it can't get > EA of those lables by LOAD_REG_IMMEDIATE(r14,interrupt_base_book3e) > and LOAD_REG_IMMEDIATE(r15,__end_interrupts),then it cases problems > later. > At the same time, r2(toc) are not usable here, so LOAD_REG_ADDR() > dosen't work neither. So we use the *name@got* to get the EV of two > lables directly. > This patch can fix the problem and remove the oops when we gdb a > program with single-step. > > Test programs test.c shows as follows: > #include > #include > int main(int argc, char *argv[]) > { > if (access("/proc/sys/kernel/perf_event_paranoid", F_OK) == -1) > printf("Kernel doesn't have perf_event support\n"); > } > > Steps to reproduce the bug, for example: > 1) ./gdb ./test > 2) (gdb) b access > 3) (gdb) r > 4) (gdb) s > > Then will trigger the oops, it looks like: > (gdb) s > Single stepping Oops: Exception in kernel mode, sig: 5 [#2] > PREEMPT CoreNet Generic > Modules linked in: > CPU: 0 PID: 1135 Comm: test Tainted: G D Linux (none) 4.9.5 #79 > task: c000000079199580 ti: c00000007ffc4000 task.ti: c000000074064000 > NIP: c00000000001a1e4 LR: 000000001000103c CTR: 000000001000100c > REGS: c00000007ffc7cf0 TRAP: 0d08 Tainted: G D (Linux (none) 4.9.5) > MSR: 0000000080021000 CR: 24000442 XER: 00000000 > SOFTE: 1 I apologize for not getting to this earlier... Does it really produce an oops, rather than a hang? It looks like without this fix, flow would go to kernel_dbg_exc which is a branch-to-self. Do you have other changes in your tree that affected this? If so, have you tested the patch on an unmodified top-of-tree kernel? I can't test this at the moment as I don't currently have hardware and QEMU doesn't emulate the booke debug registers. That said, the patch looks correct, and the bug is even worse if it's a hang rather than merely noisily killing the debugged process. It should go to stable for 4.4+ (when support for relocatable e500 was added) and probably to Linus this week (though I'd feel more comfortable knowing it got testing on the current tree). OTOH, I believe this bug will only trigger if a relocation actually happened, which on e500 is an unusual case outside of a kdump crash kernel, since the kernel is normally loaded at zero. But maybe you've got a different use case for relocatable? -Scott