From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A62FFC19F2D for ; Tue, 9 Aug 2022 09:04:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241840AbiHIJEQ (ORCPT ); Tue, 9 Aug 2022 05:04:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35552 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241807AbiHIJEM (ORCPT ); Tue, 9 Aug 2022 05:04:12 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 24CD82253C for ; Tue, 9 Aug 2022 02:04:00 -0700 (PDT) Received: from dggpemm500022.china.huawei.com (unknown [172.30.72.53]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4M26VQ70NPzjXXC; Tue, 9 Aug 2022 17:00:46 +0800 (CST) Received: from dggpemm500006.china.huawei.com (7.185.36.236) by dggpemm500022.china.huawei.com (7.185.36.162) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Tue, 9 Aug 2022 17:03:57 +0800 Received: from [10.174.178.55] (10.174.178.55) by dggpemm500006.china.huawei.com (7.185.36.236) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Tue, 9 Aug 2022 17:03:57 +0800 Subject: Re: [PATCH] ARM: Remove the special printing format of pc and lr in __show_regs() From: "Leizhen (ThunderTown)" To: "Russell King (Oracle)" CC: , , References: <20220801032016.1524-1-thunder.leizhen@huawei.com> <9f630d80-68c7-8816-f2f6-7e39c890c4d1@huawei.com> Message-ID: <1e5e5bfa-bfd5-3a0a-e4ca-a0c41bd39bd1@huawei.com> Date: Tue, 9 Aug 2022 17:03:56 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <9f630d80-68c7-8816-f2f6-7e39c890c4d1@huawei.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.178.55] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To dggpemm500006.china.huawei.com (7.185.36.236) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/8/9 10:09, Leizhen (ThunderTown) wrote: > > > On 2022/8/8 17:41, Russell King (Oracle) wrote: >> On Mon, Aug 01, 2022 at 11:20:16AM +0800, Zhen Lei wrote: >>> Currently, instruction pointers are printed in [<%08lx>] format to make >>> them more visible. However, it is not necessary in __show_regs() because >>> they have the prefix 'pc :' or 'lr :', and it is also inconsistent with >>> that of other registers, which causes misalignment. >> >> The formatting is not "to make them more visible" - it was to mark the >> addresses that we wanted the ksymoops utility to translate to kernel >> symbols before we had kallsyms in the kernel. If one disables kallsyms, >> then we still need a way to translate kernel addresses to symbols. > > I searched the git log and found that the ksymoops utility is discarded. > > See: > 073a9ecb3a73401662430bb955aedeac1de643d1 > However, a commit in the pre-git era [1] had added the statement, > "ksymoops is useless on 2.6. Please use the Oops in its original format". > > That statement existed until commit 4eb9241127a0 ("Documentation: > admin-guide: update bug-hunting.rst") finally removed the stale > ksymoops information. > > 4eb9241127a0b5ac3aaaf1b246728009527ebc86 > - delete all references to ksymoops since it is no longer applicable; > >> >> I notice there is a script which helps with this that is part of the >> kernel source - scripts/decode_stacktrace.sh. I haven't tried this on >> arm32 since I always use kallsyms - and I suspect that is rather >> universally true as it avoids needing System.map files etc to decode >> the oops. That said, if you're building a kernel for small systems, >> you probably don't want the overhead of kallsyms. Hi, Russell: I re-examined the code and found that 'pc' and 'lr' had extra printing in __show_regs(). Therefore, maybe v2 should be changed as follows, as is done in dump_backtrace_entry(): diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c index 96f3fbd51764292..2b0b49821cbf2f5 100644 --- a/arch/arm/kernel/process.c +++ b/arch/arm/kernel/process.c @@ -134,9 +134,15 @@ void __show_regs(struct pt_regs *regs) show_regs_print_info(KERN_DEFAULT); +#ifndef CONFIG_KALLSYMS + printk("PC is at [<%08lx>]\n", instruction_pointer(regs)); + printk("LR is at [<%08lx>]\n", regs->ARM_lr); +#else printk("PC is at %pS\n", (void *)instruction_pointer(regs)); printk("LR is at %pS\n", (void *)regs->ARM_lr); - printk("pc : [<%08lx>] lr : [<%08lx>] psr: %08lx\n", +#endif + + printk("pc : %08lx lr : %08lx psr: %08lx\n", regs->ARM_pc, regs->ARM_lr, regs->ARM_cpsr); printk("sp : %08lx ip : %08lx fp : %08lx\n", regs->ARM_sp, regs->ARM_ip, regs->ARM_fp); So that there are no concerns that you mentioned. CONFIG_KALLSYMS=n: PC is at [<801993d4>] LR is at [<801993d4>] pc : 801993d4 lr : 801993d4 psr: 60000013 sp : c49f9f28 ip : 00000001 fp : 00000001 CONFIG_KALLSYMS=y: PC is at ktime_get+0x4c/0xe8 LR is at ktime_get+0x4c/0xe8 pc : 8019a4ac lr : 8019a4ac psr: 60000013 sp : c49f9f28 ip : 00000001 fp : 00000001 > > Yes, I read scripts/decode_stacktrace.sh, it requires the format "[<...>]". > But if that's the only concern, maybe we can do the conversion from > "pc: addr" and "lr: addr" to "[]" first in scripts/decode_stacktrace.sh > > I'm usually "objdump -d vmlinux > asm_file", then search "addr:" in asm_file. > > Honestly, I think format "[<...>]" is dump_backtrace()'s requirement, not __show_regs()'s. > > >> >> So, there's an argument for keeping it - it's an API in that it >> provides hints to scripting to identify which values need to be >> converted to symbols. There's also the argument for getting rid of it, >> which is that hardly anyone does that anymore. >> >> The question is, which is the more important argument, and I don't >> think there's a definite answer. So I'm inclined to leave this >> as-is. > > OK > >> > -- Regards, Zhen Lei