linux-kernel - Re: [PATCH v10 16/17] module: fix types of device tables aliases

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Message-Id: <20150129151314.8b3951ff70d67cde9223f927@linux-foundation.org>
Date:	Thu, 29 Jan 2015 15:13:14 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andrey Ryabinin <a.ryabinin@...sung.com>
Cc:	linux-kernel@...r.kernel.org, Dmitry Vyukov <dvyukov@...gle.com>,
	Konstantin Serebryany <kcc@...gle.com>,
	Dmitry Chernenkov <dmitryc@...gle.com>,
	Andrey Konovalov <adech.fo@...il.com>,
	Yuri Gribov <tetra2005@...il.com>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Christoph Lameter <cl@...ux.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Dave Hansen <dave.hansen@...el.com>,
	Andi Kleen <andi@...stfloor.org>, x86@...nel.org,
	linux-mm@...ck.org, Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH v10 16/17] module: fix types of device tables aliases

On Thu, 29 Jan 2015 18:12:00 +0300 Andrey Ryabinin <a.ryabinin@...sung.com> wrote:

> MODULE_DEVICE_TABLE() macro used to create aliases to device tables.
> Normally alias should have the same type as aliased symbol.
> 
> Device tables are arrays, so they have 'struct type##_device_id[x]'
> types. Alias created by MODULE_DEVICE_TABLE() will have non-array type -
> 	'struct type##_device_id'.
> 
> This inconsistency confuses compiler, it could make a wrong
> assumption about variable's size which leads KASan to
> produce a false positive report about out of bounds access.

The changelog describes the problem but doesn't describe how the patch
addresses the problem.  Some more details would be useful.

> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -135,7 +135,7 @@ void trim_init_extable(struct module *m);
>  #ifdef MODULE
>  /* Creates an alias so file2alias.c can find device table. */
>  #define MODULE_DEVICE_TABLE(type, name)					\
> -  extern const struct type##_device_id __mod_##type##__##name##_device_table \
> +extern typeof(name) __mod_##type##__##name##_device_table \
>    __attribute__ ((unused, alias(__stringify(name))))

We lost the const?  If that's deliberate then why?  What are the
implications?  Do the device tables now go into rw memory?
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