linux-kernel - Re: [PATCH 5/6] module: make modversion_info contain a pointer, not an array.

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Message-ID: <20090205160128.GA9486@mediacenter>
Date:	Thu, 5 Feb 2009 10:01:28 -0600
From:	Shawn Bohrer <shawn.bohrer@...il.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/6] module: make modversion_info contain a pointer,
	not an array.

On Thu, Jan 29, 2009 at 12:05:52AM +1030, Rusty Russell wrote:
> With allmodconfig (minus non-building modules) on 32-bit x86:
> Total size of modules before: 60009790 bytes
> Total size of modules after: 55927866 bytes
> 
> Saving 7% of module size for CONFIG_MODVERSIONS=y; and these sections
> are kept resident as well.
> 
> Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
> ---
>  include/linux/module.h |    4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/module.h b/include/linux/module.h
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -37,10 +37,12 @@ struct kernel_symbol
>  	const char *name;
>  };
>  
> +/* This is put in the __versions section of a module to indicate the version
> + * it expects for unknown symbols. */
>  struct modversion_info
>  {
>  	unsigned long crc;
> -	char name[MODULE_NAME_LEN];
> +	char *name;
>  };

Hey Rusty thanks for the change, but I just got around to testing this
and I have a few observations/questions.  First this breaks:

modprobe --dump-modversions foo.ko

I actually don't care, but just happened to stumble upon it when I also
noticed that your changes seemed to be working a little too well.  I
currently happen to be building my modules out of order for example
module B depends on symbols from module A, but I build module B first.
This means that the exported symbols are not in the Module.symvers file
when module B is compiled.  I would expect module B to fail to load yet
with your patches it magically works and I don't see any errors in the
logs.  If I run:

objdump -s --section __versions B.ko

I only get something like:

Contents of section __versions:
 0000 d782ec86 00000000

Of course if I build the modules in the correct order and dump the
__versions section I see the correct number of crc/char* pairs.

--
Shawn
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