linux-kernel - Re: memcmp in modules

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Message-ID: <51771610.5040303@zytor.com>
Date:	Tue, 23 Apr 2013 16:15:28 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Rusty Russell <rusty@...tcorp.com.au>
CC:	andy.shevchenko@...il.com, arjan@...radead.org,
	linux-kernel@...r.kernel.org
Subject: Re: memcmp in modules

On 04/22/2013 07:26 AM, Tetsuo Handa wrote:
> Andy Shevchenko wrote:
>> What did I miss?
> 
> Well, as of linux-next-20130422, memcmp() is not correctly exported to modules.
> Since linux-3.9-rc8 correctly exports memcmp(), this problem seems to be introduced
> in linux-next tree. Also, this problem seems to involve CONFIG_MODVERSIONS=y.
> 
>   [root@...alhost linux-next]# modprobe ipv6
>   FATAL: Error inserting ipv6 (/lib/modules/3.9.0-rc8-next-20130422/kernel/net/ipv6/ipv6.ko): Invalid argument
>   [root@...alhost linux-next]# dmesg
>   ipv6: no symbol version for memcmp
>   ipv6: Unknown symbol memcmp (err -22)
> 
> Since arch/x86/include/asm/string_64.h uses
> 
>   int memcmp(const void *cs, const void *ct, size_t count);
> 
> while arch/x86/include/asm/string_32.h uses
> 
>   #define memcmp __builtin_memcmp
> 
> changing to what you have tried
> 
>   #define memcmp(a, b, n) __builtin_memcmp(a, b, n)
> 
> or changing to what x86_64 does
> 
>   int memcmp(const void *cs, const void *ct, size_t count);
> 
> might solve this problem. But I don't know which one is correct solution...
> 

Rusty, this seems like a problem with your changes to the prefix
handling.  Somehow memcmp being a macro gets picked up by some, but not
all, of the module-metadata generation tools.

Changing memcmp to a macro with arguments (see above) seems to paper
over the problem for this one, but there seems to be something much more
sinister going on and I would really like a good explanation as I fear
this can crop up in other places.

	-hpa

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