linux-kernel - Re: [PATCH 1/9] LoongArch/ftrace: Add basic support

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Message-ID: <de7584d4-56ff-aafe-42ec-702924fbcf64@loongson.cn>
Date:   Sat, 20 Aug 2022 11:16:03 +0800
From:   Jinyang He <hejinyang@...ngson.cn>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Qing Zhang <zhangqing@...ngson.cn>,
        Huacai Chen <chenhuacai@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        WANG Xuerui <kernel@...0n.name>, loongarch@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        Jiaxun Yang <jiaxun.yang@...goat.com>
Subject: Re: [PATCH 1/9] LoongArch/ftrace: Add basic support

On 08/20/2022 09:52 AM, Steven Rostedt wrote:

> On Sat, 20 Aug 2022 09:38:21 +0800
> Jinyang He <hejinyang@...ngson.cn> wrote:
>
>> I think we have implemented CONFIG_FTRACE_WITH_ARGS in dynamic ftrace
>> in the [Patch3/9].
> Sorry, I must have missed it.
And there is still something left to do, Qing will do that.

>
>> But, for non dynamic ftrace, it is hardly to
>> implement it. Because the LoongArch compiler gcc treats mount as a
> Don't bother implementing it for non-dynamic. I would just add a:
>
> config HAVE_FTRACE_WITH_ARGS if DYNAMIC_FTRACE
>
> and be done with it.
Yes, it is clear.

>
>> really call, like 'call _mcount(__builtin_return_address(0))'. That
>> means, they decrease stack, save args to callee saved regs and may
>> do some optimization before calling mcount. It is difficult to find the
>> original args and apply changes from tracers.
> Right, there's no point in implementing it for non dynamic. Like I said,
> non-dynamic is just a stepping stone for getting dynamic working. Once you
> have dynamic working, it's up to you to throw out the non-dynamic. It's not
> useful for anything other than porting to a new architecture or for
> academic purposes.
>
Thanks for your detail answers.
Jinyang