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 A4AC0C74A5B for ; Tue, 21 Mar 2023 14:31:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230404AbjCUObk (ORCPT ); Tue, 21 Mar 2023 10:31:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56168 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229726AbjCUObh (ORCPT ); Tue, 21 Mar 2023 10:31:37 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 02CAD3C16; Tue, 21 Mar 2023 07:31:35 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 397B6AD7; Tue, 21 Mar 2023 07:25:18 -0700 (PDT) Received: from FVFF77S0Q05N (unknown [10.57.54.220]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 4ADBD3F6C4; Tue, 21 Mar 2023 07:24:31 -0700 (PDT) Date: Tue, 21 Mar 2023 14:24:28 +0000 From: Mark Rutland To: Donglin Peng Cc: mhiramat@kernel.org, rostedt@goodmis.org, linux@armlinux.org.uk, will@kernel.org, catalin.marinas@arm.com, palmer@dabbelt.com, paul.walmsley@sifive.com, tglx@linutronix.de, dave.hansen@linux.intel.com, x86@kernel.org, mingo@redhat.com, xiehuan09@gmail.com, dinghui@sangfor.com.cn, huangcun@sangfor.com.cn, dolinux.peng@gmail.com, linux-trace-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 1/2] function_graph: Support recording and printing the return value of function Message-ID: References: <20230320131650.482594-1-pengdonglin@sangfor.com.cn> <20230320131650.482594-2-pengdonglin@sangfor.com.cn> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230320131650.482594-2-pengdonglin@sangfor.com.cn> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 20, 2023 at 06:16:49AM -0700, Donglin Peng wrote: > When using the function_graph tracer to analyze system call failures, > it can be time-consuming to analyze the trace logs and locate the kernel > function that first returns an error. This change aims to simplify the > process by recording the function return value to the 'retval' member of > 'ftrace_graph_ent' and printing it when outputing the trace log. > > New trace options are introduced: funcgraph-retval and graph_retval_hex. > The former is used to control whether to display the return value, while > the latter is used to control the display format of the reutrn value. > > Note that even if a function's return type is void, a return value will > still be printed, so just ignore it. > > Currently, this modification supports the following commonly used > processor architectures: x86_64, x86, arm64, arm, riscv. > > Here is an example: > > I want to attach the demo process to a cpu cgroup, but it failed: > > echo `pidof demo` > /sys/fs/cgroup/cpu/test/tasks > -bash: echo: write error: Invalid argument > > The strace logs tells that the write system call returned -EINVAL(-22): > ... > write(1, "273\n", 4) = -1 EINVAL (Invalid argument) > ... > > Use the following commands to capture trace logs when calling the write > system call: > > cd /sys/kernel/debug/tracing/ > echo 0 > tracing_on > echo > trace > echo *sys_write > set_graph_function > echo *spin* > set_graph_notrace > echo *rcu* >> set_graph_notrace > echo *alloc* >> set_graph_notrace > echo preempt* >> set_graph_notrace > echo kfree* >> set_graph_notrace > echo $$ > set_ftrace_pid > echo function_graph > current_tracer > echo 1 > tracing_on > echo `pidof demo` > /sys/fs/cgroup/cpu/test/tasks > echo 0 > tracing_on > echo 1 > options/funcgraph-retval > cat trace > ~/trace.log > > Search the error code -22 directly in the file trace.log and find the > first function that return -22, then read the function code to get the > root cause. > > ... > > 1) | cgroup_migrate() { > 1) 0.651 us | cgroup_migrate_add_task(); /* = 0xffff93fcfd346c00 */ > 1) | cgroup_migrate_execute() { > 1) | cpu_cgroup_can_attach() { > 1) | cgroup_taskset_first() { > 1) 0.732 us | cgroup_taskset_next(); /* = 0xffff93fc8fb20000 */ > 1) 1.232 us | } /* cgroup_taskset_first = 0xffff93fc8fb20000 */ > 1) 0.380 us | sched_rt_can_attach(); /* = 0x0 */ > 1) 2.335 us | } /* cpu_cgroup_can_attach = -22 */ > 1) 4.369 us | } /* cgroup_migrate_execute = -22 */ > 1) 7.143 us | } /* cgroup_migrate = -22 */ > > ... > > Signed-off-by: Donglin Peng > diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S > index 350ed81324ac..d1a5d76e6d72 100644 > --- a/arch/arm64/kernel/entry-ftrace.S > +++ b/arch/arm64/kernel/entry-ftrace.S > @@ -276,7 +276,15 @@ SYM_CODE_START(return_to_handler) > stp x4, x5, [sp, #32] > stp x6, x7, [sp, #48] > > +#ifdef CONFIG_FUNCTION_GRAPH_RETVAL > + /* > + * Pass both the function return values in the register x0 and x1 > + * to ftrace_return_to_handler. > + */ > + mov x2, x29 // parent's fp > +#else > mov x0, x29 // parent's fp > +#endif > bl ftrace_return_to_handler// addr = ftrace_return_to_hander(fp); > mov x30, x0 // restore the original return address Please don't make the calling convention of the asm change depending on a selectable config option. We already store the regs here; I'd be happy to make that a struct ftrace_regs and pass a pointer to that to C code. Then it's be easy to acquire the value you want in the exact same way as upon entry, and it'll work even if we decide to return a structure by value somewhere (as that can use registers x2-x7 too). Thanks, Mark.