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

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Date:   Wed, 24 Mar 2021 16:10:54 +0000
From:   Qais Yousef <qais.yousef@....com>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Alexander Sverdlin <alexander.sverdlin@...ia.com>,
        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>
Subject: Re: [PATCH v7 2/2] ARM: ftrace: Add MODULE_PLTS support

Hi Florian

On 03/23/21 20:37, Florian Fainelli wrote:
> Hi Qais,
> 
> On 3/23/2021 3:22 PM, Qais Yousef wrote:
> > Hi Alexander
> > 
> > On 03/22/21 18:02, Alexander Sverdlin wrote:
> >> Hi Qais,
> >>
> >> On 22/03/2021 17:32, 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.
> 
> Your patch in addition to Alexander's patch work for me as well, so feel
> free to add a:
> 
> Tested-by: Florian Fainelli <f.fainelli@...il.com>
> 
> FWIW, what is nice about Alexander's original patch is that it applies
> relatively cleanly to older kernels as well where this is equally

How old are we talking? Was the conflict that bad for the stable maintainers to
deal with it? ie: would it require sending the backport separately?

> needed. There is not currently any Fixes: tag being provided but maybe
> we should amend the second patch with one?

I'm not sure if this will be considered new feature or a bug fix. FWIW,
tagging it for stable sounds reasonable to me.

Thanks!

--
Qais Yosuef