From: Ding Hui <dinghui@sangfor.com.cn>
To: Donglin Peng <pengdonglin@sangfor.com.cn>,
mhiramat@kernel.org, rostedt@goodmis.org, linux@armlinux.org.uk,
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, huangcun@sangfor.com.cn,
dolinux.peng@gmail.com
Cc: 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 2/2] tracing: Add documentation for funcgraph-retval and graph_retval_hex
Date: Tue, 21 Mar 2023 10:31:21 +0800 [thread overview]
Message-ID: <4a88721a-ac78-bcad-1b33-f9027baab5ab@sangfor.com.cn> (raw)
In-Reply-To: <20230320131650.482594-3-pengdonglin@sangfor.com.cn>
On 2023/3/20 21:16, Donglin Peng wrote:
> +There are some limitations when using the funcgraph-retval currently:
> +
> +- Even if the function return type is void, a return value will still
> + be printed, and you can just ignore it.
> +
> +- Even if the return value is not an error code actually, it may be
> + displayed as an error code. You should read the code to check.
> + For example, both 0xfe and 0xfffe are be interpreted as -2.
For char and short types, displaying as signed decimal may be not
appropriate, because they are rarely used to store error code.
So in "smart" mode (graph_retval_hex=0), I suggest just smart convert
error value stored in int or pointer to signed decimal.
> +- Only the value of the first return register will be recorded and
> + printed even if the return values may be stored in two registers
> + actually. For example, both the eax and edx are used to store a
> + 64 bit return value in the x86 architecture, and the eax stores
> + the low 32 bit, the edx stores the high 32 bit, however only the
> + value stored in eax will be recorded and printed.
> +
> You can put some comments on specific functions by using
> trace_printk() For example, if you want to put a comment inside
> the __might_sleep() function, you just have to include
--
Thanks,
- Ding Hui
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next prev parent reply other threads:[~2023-03-21 2:31 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)
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 [this message]
2023-03-21 3:24 ` Donglin Peng
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