From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Donglin Peng <pengdonglin@sangfor.com.cn>
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
Date: Tue, 21 Mar 2023 17:31:45 +0000 [thread overview]
Message-ID: <ZBnqAYO7rdk4Qikq@shell.armlinux.org.uk> (raw)
In-Reply-To: <20230320131650.482594-2-pengdonglin@sangfor.com.cn>
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!
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next prev parent reply other threads:[~2023-03-21 17:34 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-20 13:16 [PATCH v5 0/2] function_graph: Support recording and printing the return value of function Donglin Peng
2023-03-20 13:16 ` [PATCH v5 1/2] " Donglin Peng
2023-03-21 14:09 ` Florian Kauer
2023-03-21 14:44 ` Steven Rostedt
2023-03-21 15:11 ` Florian Kauer
2023-03-22 5:01 ` Donglin Peng
2023-03-21 14:24 ` Mark Rutland
2023-03-22 8:47 ` Donglin Peng
2023-03-21 17:31 ` Russell King (Oracle) [this message]
2023-03-22 9:01 ` Donglin Peng
2023-03-20 13:16 ` [PATCH v5 2/2] tracing: Add documentation for funcgraph-retval and graph_retval_hex Donglin Peng
2023-03-21 2:31 ` Ding Hui
2023-03-21 3:24 ` Donglin Peng
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