linux-kernel - RE: Re: [PATCH 1/1] arm/module: maximum utilization of module area.

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Date:   Mon, 12 Dec 2016 11:22:30 +0000
From:   Vaneet Narang <v.narang@...sung.com>
To:     Russell King - ARM Linux 
        <linux@...linux.org.uk>,
        Maninder Singh <maninder1.s@...sung.com>
Cc:     nicolas.pitre@...aro.org 
        <nicolas.pitre@...aro.org>,
        ssantosh@...nel.org <ssantosh@...nel.org>,
        panand@...hat.com <panand@...hat.com>,
        arnd@...db.de <arnd@...db.de>,
        chris.brandt@...esas.com 
        <chris.brandt@...esas.com>,
        linux-arm-kernel@...ts.infradead.org 
        <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel@...r.kernel.org 
        <linux-kernel@...r.kernel.org>,
        PANKAJ MISHRA <pankaj.m@...sung.com>,
        Ajeet Kumar Yadav <ajeet.y@...sung.com>
Subject: RE: Re: [PATCH 1/1] arm/module: maximum utilization of module area.

Hi,

>A PC24 relocation has a range of +/-32MB.  This means that where-ever
>the module is placed, it must be capable of reaching any function
>within the kernel text, which may itself be quite large (eg, 8MB, or
>possibly larger).  The module area exists to allow modules to be
>located in an area where PC24 relocations are able to reach all of the
>kernel text on sensibly configured kernels, thereby allowing for
>optimal performance.
>
>If you wish to load large modules, then enable ARM_MODULE_PLTS, which
>will use the less efficient PLT method (which is basically an indirect
>function call) for relocations that PC24 can't handle, and will allow
>the module to be loaded into the vmalloc area.
>
>Growing the module area so that smaller modules also get penalised by
>the PLT indirection is not sane.

This is exactly what i am saying. These changes are useful to accomdate
22MB modules without enabling ARM_MODULE_PLTS. 
Without these changes ARM_MODULE_PLTS needs to be enabled to insert more than 14MB
modules but with these changes 22MB modules (considering 8MB uImage) can be inserted 
without enabling ARM_MODULE_PLTS.

So till 22MB modules are not penalised but without these changes once size of modules
gets over 14MB PLT becomes must. 

Regards,
Vaneet Narang