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

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Message-ID: <540FFDD5.8000403@mentor.com>
Date:	Wed, 10 Sep 2014 15:29:25 +0800
From:	Chung-Lin Tang <chunglin_tang@...tor.com>
To:	<Valdis.Kletnieks@...edu>, Ley Foon Tan <lftan@...era.com>
CC:	<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 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?

Chung-Lin

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