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Subject: Re: [PATCH 1/9] LoongArch/ftrace: Add basic support
To:     Steven Rostedt <rostedt@goodmis.org>
References: <20220819081403.7143-1-zhangqing@loongson.cn>
 <20220819081403.7143-2-zhangqing@loongson.cn>
 <20220819132509.127a1353@gandalf.local.home>
 <246779c0-b834-16a6-ec68-c06d8f9a375d@loongson.cn>
 <20220819215240.3caf89e2@gandalf.local.home>
Cc:     Qing Zhang <zhangqing@loongson.cn>,
        Huacai Chen <chenhuacai@kernel.org>,
        Ingo Molnar <mingo@redhat.com>,
        WANG Xuerui <kernel@xen0n.name>, loongarch@lists.linux.dev,
        linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
        Jiaxun Yang <jiaxun.yang@flygoat.com>
From:   Jinyang He <hejinyang@loongson.cn>
Message-ID: <de7584d4-56ff-aafe-42ec-702924fbcf64@loongson.cn>
Date:   Sat, 20 Aug 2022 11:16:03 +0800
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On 08/20/2022 09:52 AM, Steven Rostedt wrote:

> On Sat, 20 Aug 2022 09:38:21 +0800
> Jinyang He <hejinyang@loongson.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