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Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:51692) by pandora.armlinux.org.uk with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1pefq5-0001da-I2; Tue, 21 Mar 2023 17:32:01 +0000 Received: from linux by shell.armlinux.org.uk with local (Exim 4.94.2) (envelope-from ) id 1pefpp-0007vh-5A; Tue, 21 Mar 2023 17:31:45 +0000 Date: Tue, 21 Mar 2023 17:31:45 +0000 From: "Russell King (Oracle)" To: Donglin Peng 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 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-Disposition: inline In-Reply-To: <20230320131650.482594-2-pengdonglin@sangfor.com.cn> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230321_103229_067505_9EE842F0 X-CRM114-Status: GOOD ( 14.88 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Mar 20, 2023 at 06:16:49AM -0700, Donglin Peng wrote: > diff --git a/arch/arm/kernel/entry-ftrace.S b/arch/arm/kernel/entry-ftrace.S > index 3e7bcaca5e07..ba1986e27af8 100644 > --- a/arch/arm/kernel/entry-ftrace.S > +++ b/arch/arm/kernel/entry-ftrace.S > @@ -258,7 +258,15 @@ ENDPROC(ftrace_graph_regs_caller) > #ifdef CONFIG_FUNCTION_GRAPH_TRACER > ENTRY(return_to_handler) > stmdb sp!, {r0-r3} > +#ifdef CONFIG_FUNCTION_GRAPH_RETVAL > + /* > + * Pass both the function return values in the register r0 and r1 > + * to ftrace_return_to_handler > + */ > + add r2, sp, #16 @ sp at exit of instrumented routine > +#else > add r0, sp, #16 @ sp at exit of instrumented routine > +#endif > bl ftrace_return_to_handler ... > -unsigned long ftrace_return_to_handler(unsigned long frame_pointer) > +static unsigned long __ftrace_return_to_handler(unsigned long retval_1st, > + unsigned long retval_2nd, unsigned long frame_pointer) ... > +#ifdef CONFIG_FUNCTION_GRAPH_RETVAL > +unsigned long ftrace_return_to_handler(unsigned long retval_1st, > + unsigned long retval_2nd, unsigned long frame_pointer) > +{ > + return __ftrace_return_to_handler(retval_1st, retval_2nd, frame_pointer); > +} > +#else > +unsigned long ftrace_return_to_handler(unsigned long frame_pointer) > +{ > + return __ftrace_return_to_handler(0, 0, frame_pointer); > +} > +#endif > + Hi, To echo Mark's criticism, I also don't like this. I feel it would be better if ftrace_return_to_handler() always took the same arguments irrespective of the setting of CONFIG_FUNCTION_GRAPH_RETVAL. On 32-bit ARM, we have to stack r0-r3 anyway to prevent the call to ftrace_return_to_handler() corrupting the return value, and these are the registers we need. So we might as well pass a pointer to these stacked registers. Whether that's acceptable on other architectures, I couldn't say. Thanks. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last! _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel