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Subject: Re: [PATCH v7 2/2] ARM: ftrace: Add MODULE_PLTS support
To:     Qais Yousef <qais.yousef@arm.com>
Cc:     Steven Rostedt <rostedt@goodmis.org>,
        Ingo Molnar <mingo@redhat.com>,
        Russell King <linux@armlinux.org.uk>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        Ard Biesheuvel <ardb@kernel.org>,
        Linus Walleij <linus.walleij@linaro.org>,
        Florian Fainelli <f.fainelli@gmail.com>
References: <e726be33-bc03-0515-f430-c5a34ebc3619@nokia.com>
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From:   Alexander Sverdlin <alexander.sverdlin@nokia.com>
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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.