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 93428C6FD1F for ; Fri, 17 Mar 2023 02:50:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229631AbjCQCuH (ORCPT ); Thu, 16 Mar 2023 22:50:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38894 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229680AbjCQCuF (ORCPT ); Thu, 16 Mar 2023 22:50:05 -0400 Received: from mail-m118111.qiye.163.com (mail-m118111.qiye.163.com [115.236.118.111]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F07116A9F4; Thu, 16 Mar 2023 19:50:01 -0700 (PDT) Received: from [172.23.196.229] (unknown [121.32.254.147]) by mail-m118111.qiye.163.com (Hmail) with ESMTPA id DFE60580599; Fri, 17 Mar 2023 10:49:49 +0800 (CST) Message-ID: <34781b74-8d3e-a7e6-9abe-e8d45d680eec@sangfor.com.cn> Date: Fri, 17 Mar 2023 10:49:49 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.8.0 From: Donglin Peng Subject: Re: [PATCH v4 1/2] function_graph: Support recording and printing the return value of function To: "Russell King (Oracle)" Cc: mhiramat@kernel.org, rostedt@goodmis.org, mark.rutland@arm.com, 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 References: <20230315133911.958741-1-pengdonglin@sangfor.com.cn> <20230315133911.958741-2-pengdonglin@sangfor.com.cn> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-HM-Spam-Status: e1kfGhgUHx5ZQUpXWQgPGg8OCBgUHx5ZQUlOS1dZFg8aDwILHllBWSg2Ly tZV1koWUFITzdXWS1ZQUlXWQ8JGhUIEh9ZQVkaSB4eVk1OSxlOHRpMTkpNH1UTARMWGhIXJBQOD1 lXWRgSC1lBWUpJSlVISVVJTk9VSk9MWVdZFhoPEhUdFFlBWU9LSFVKSktPSEhVSktLVUtZBg++ X-HM-Sender-Digest: e1kMHhlZQR0aFwgeV1kSHx4VD1lBWUc6PCI6PRw6PT0NSB9CNyk*NA8x QzkwCVFVSlVKTUxCS0lKSEJKT09KVTMWGhIXVQseFRwfFBUcFxIVOwgaFRwdFAlVGBQWVRgVRVlX WRILWUFZSklKVUhJVUlOT1VKT0xZV1kIAVlBT0xOTTcG X-HM-Tid: 0a86ed793c992eb7kusndfe60580599 X-HM-MType: 1 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2023/3/17 7:21, Russell King (Oracle) wrote: > On Wed, Mar 15, 2023 at 06:39:10AM -0700, Donglin Peng wrote: >> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig >> index e24a9820e12f..ad03fc868f34 100644 >> --- a/arch/arm/Kconfig >> +++ b/arch/arm/Kconfig >> @@ -99,6 +99,7 @@ config ARM >> select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL >> select HAVE_FUNCTION_ERROR_INJECTION >> select HAVE_FUNCTION_GRAPH_TRACER >> + select HAVE_FUNCTION_GRAPH_RETVAL if HAVE_FUNCTION_GRAPH_TRACER >> select HAVE_FUNCTION_TRACER if !XIP_KERNEL >> select HAVE_GCC_PLUGINS >> select HAVE_HW_BREAKPOINT if PERF_EVENTS && (CPU_V6 || CPU_V6K || CPU_V7) >> diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S >> index 3e7bcaca5e07..0151d2ce9958 100644 >> --- a/arch/arm/kernel/entry-ftrace.S >> +++ b/arch/arm/kernel/entry-ftrace.S >> @@ -258,6 +258,10 @@ ENDPROC(ftrace_graph_regs_caller) >> #ifdef CONFIG_FUNCTION_GRAPH_TRACER >> ENTRY(return_to_handler) >> stmdb sp!, {r0-r3} >> +#ifdef CONFIG_FUNCTION_GRAPH_RETVAL >> + /* Pass the function return value to ftrace_return_to_handler */ >> + mov r1, r0 > > In a similar vein to Peter's comment, do we care about 64-bit return > values here, because the above only covers 32-bit values. > > If we do care about 64-bit values, then we get into EABI/OABI > stickyness, because on EABI the 64-bit value would have to be passed > in r2,r3, and OABI would need r1,r2. > > it would be better to have the 64-bit argument as the first argument > to ftrace_return_to_handler() which would eliminate that variability, > but I don't know what effect that would have for other architectures. > > Things get more icky if we want 128-bit values. For EABI, we've > conveniently just stacked that. For OABI, that would need to be in > r1-r3 and the final high bits on the stack. > > With a 128-bit argument as the first, that would be r0-r3 with the > existing stack pointer argument stored... on the stack. > > So, really it depends what size of return value we want to report. > Also, please bear in mind that where a function returns a 32-bit > value, that will be in r0, and r1 will be whatever happened to be > in it at function exit - there's no defined value for r1. > Thank you. I will document this as a limitation of fgraph return value. It can just cover most cases at present and I think the r0 is enough.