linux-kernel - Re: [PATCH RFC] ARM: option for loading modules into vmalloc area

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Message-ID: <alpine.LFD.2.11.1411191205530.11690@knanqh.ubzr>
Date:	Wed, 19 Nov 2014 12:12:18 -0500 (EST)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
cc:	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	Arnd Bergmann <arnd@...db.de>,
	Andrey Ryabinin <a.ryabinin@...sung.com>,
	Konstantin Khlebnikov <k.khlebnikov@...sung.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH RFC] ARM: option for loading modules into vmalloc area

On Wed, 19 Nov 2014, Russell King - ARM Linux wrote:

> On Wed, Nov 19, 2014 at 11:57:15AM -0500, Nicolas Pitre wrote:
> > On Wed, 19 Nov 2014, Russell King - ARM Linux wrote:
> > > I don't think I ever did, because its pretty much impossible to do as I
> > > explained in a follow up to this thread.
> > > 
> > > We _used_ to do this with the userspace insmod methods, but since we got
> > > this kernel-side linker, it's been pretty much impossible to do without
> > > rewriting the module code.  That's not going to happen on account of one
> > > quirky architecture which Linus doesn't particularly like.
> > 
> > Still... We could try adding a hook in the generic module linker code 
> > for a pre-relocation pass.  Maybe only ARM would use it, but if the need 
> > to load big modules is real then I imagine Linus could be amenable to a 
> > compromise.
> 
> So, how big a table would you allocate for the trampolines, based upon
> not knowing anything about the module being loaded?  4K?  8K?  64K?

The idea of a pre-relocation pass is to determine that.  That could be 
something similar to calling apply_relocate() twice: once to determine 
the number of trampoline entries, and a second time to perform the 
actual relocation.


Nicolas
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