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

[Jinyang He <hejinyang@loongson.cn>]

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