linux-kernel - Re: [PATCH v3 25/29] nios2: Module support

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Message-ID: <20140910074959.GA14260@distanz.ch>
Date:	Wed, 10 Sep 2014 09:49:59 +0200
From:	Tobias Klauser <tklauser@...tanz.ch>
To:	Chung-Lin Tang <chunglin_tang@...tor.com>
Cc:	Arnd Bergmann <arnd@...db.de>, Valdis.Kletnieks@...edu,
	Ley Foon Tan <lftan@...era.com>, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	lftan.linux@...il.com, cltang@...esourcery.com
Subject: Re: [PATCH v3 25/29] nios2: Module support

On 2014-09-10 at 09:29:25 +0200, Chung-Lin Tang <chunglin_tang@...tor.com> wrote:
> On 14/9/10 5:25 AM, Valdis.Kletnieks@...edu wrote:
> > On Mon, 08 Sep 2014 17:22:36 +0800, Ley Foon Tan said:
> >> This patch adds support for loadable modules.
> >>
> >> Signed-off-by: Ley Foon Tan <lftan@...era.com>
> > 
> >> +/*
> >> + * Modules should NOT be allocated with kmalloc for (obvious) reasons.
> >> + * But we do it for now to avoid relocation issues. CALL26/PCREL26 cannot reach
> >> + * from 0x80000000 (vmalloc area) to 0xc00000000 (kernel) (kmalloc returns
> >> + * addresses in 0xc0000000)
> >> + */
> > 
> > That's a nice scary comment to see. :)
> > 
> > What's the long-term plan here?
> > 
> 
> We would probably need to add the ability to add trampolines in some
> way, though this of course impairs a little performance. Or if the
> default region of vmalloc can be configured to use the same 256MB region
> as the kernel.
> 
> I wonder how MIPS (which has similar same-region call/jump instructions)
> deals with this?

Please see Arnd's comment on the v2 of this patch [1] for a solution.

[1] http://www.spinics.net/lists/linux-arch/msg27059.html
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