linux-kernel - Re: [PATCH v7 2/2] ARM: ftrace: Add MODULE

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Message-ID: <25056e99-dfd1-645b-39fc-14f47085a7fe@nokia.com>
Date:   Wed, 24 Mar 2021 10:04:42 +0100
From:   Alexander Sverdlin <alexander.sverdlin@...ia.com>
To:     Qais Yousef <qais.yousef@....com>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Ard Biesheuvel <ardb@...nel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Florian Fainelli <f.fainelli@...il.com>
Subject: Re: [PATCH v7 2/2] ARM: ftrace: Add MODULE_PLTS support

Hi Qais,

On 23/03/2021 23:22, Qais Yousef wrote:
>>> Yes you're right. I was a bit optimistic on CONFIG_DYNAMIC_FTRACE will imply
>>> CONFIG_ARM_MODULE_PLTS is enabled too.
>>>
>>> It only has an impact on reducing ifdefery when calling
>>>
>>> 	ftrace_call_replace_mod(rec->arch.mod, ...)
>>>
>>> Should be easy to wrap rec->arch.mod with its own accessor that will return
>>> NULL if !CONFIG_ARM_MODULE_PLTS or just ifdef the functions.
>>>
>>> Up to Alexander to pick what he prefers :-)
>> well, I of course prefer v7 as-is, because this review is running longer than two
>> years and I actually hope these patches to be finally merged at some point.
>> But you are welcome to optimize them with follow up patches :)
> I appreciate that and thanks a lot for your effort. My attempt to review and
> test here is to help in getting this merged.
> 
> FWIW my main concern is about duplicating the range check in
> ftrace_call_replace() and using magic values that already exist in
> __arm_gen_branch_{arm, thumb2}() and better remain encapsulated there.

could you please check the negative limits? I have an opinion, my limits are
correct. I could add extra parameter to arm_gen_branch_link(), but for this
I first need to fix its negative limits, which, I believe, well... Approximate :)

-- 
Best regards,
Alexander Sverdlin.