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

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Message-ID: <169a0b1e-beee-bae6-8625-9b9ceb8bb0ea@nokia.com>
Date:   Wed, 24 Mar 2021 17:33:12 +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

Hello Qais,

On 24/03/2021 16:57, Qais Yousef wrote:
>>> 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 :)
> Can you elaborate please?
> 
> If you look at Arm ARM [1] the ranges are defined in page 347
> 
> 	Encoding T1 Even numbers in the range –16777216 to 16777214.
> 	Encoding T2 Multiples of 4 in the range –16777216 to 16777212.
> 	Encoding A1 Multiples of 4 in the range –33554432 to 33554428.
> 	Encoding A2 Even numbers in the range –33554432 to 33554430.
> 
> which matches what's in the code (T1 for thumb2 and A1 for arm).
> 
> Why do you think it's wrong?

thanks for checking this! I'll re-send v8 with your proposal.

-- 
Best regards,
Alexander Sverdlin.