linux-kernel - Re: [PATCH] x86_32: Fix module version table mismatch.

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Date:	Wed, 24 Apr 2013 16:49:33 +0300
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	James Hogan <james.hogan@...tec.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	Arjan van de Ven <arjan@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86_32: Fix module version table mismatch.

It works
Tested-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

On Wed, Apr 24, 2013 at 1:13 PM, James Hogan <james.hogan@...tec.com> wrote:
> On 24/04/13 02:00, H. Peter Anvin wrote:
>> On 04/23/2013 05:52 PM, H. Peter Anvin wrote:
>>> On 04/23/2013 05:40 AM, Tetsuo Handa wrote:
>>>> Commit a4b6a77b "module: fix symbol versioning with symbol prefixes" broke
>>>> loading of net/ipv6/ipv6.ko built with CONFIG_MODVERSIONS=y for x86_32.
>>>
>>> This really does seem to be the offending commit, although I'm still
>>> confused how the heck that is possible.
>>>
>>
>> OK, now I grok.
>>
>> The bug is the use of VMLINUX_SYMBOL_STR(%s) which expands at the time
>> the output of modpost is compiled.  However, VMLINUX_SYMBOL_STR() unlike
>> __VMLINUX_SYMBOL_STR() does macro expansion on its argument, which is
>> actively wrong here.
>
> Yes, nasty bug there (sorry!)
>
>> I think the choice is either to change this to __VMLINUX_SYMBOL_STR() or
>> re-introduce CONFIG_SYMBOL_PREFIX (or its equivalent) so that modprobe
>> can emit it at compile time
>
> Using __VMLINUX_SYMBOL_STR looks like the correct solution to me.
>
>> (assuming there even should *be* a prefix on
>> the symbol here, i.e. that the compiler won't add it.)
>
> [__]VMLINUX_SYMBOL_STR expands to a string (e.g. "_" "memcmp" or just
> "memcmp") so the compiler won't touch it.
>
>>
>> Either way -- James, Rusty, this is in your court.
>
> How does the patch below look? I presume this is preferred over
> making VMLINUX_SYMBOL_STR non-argument-expanding?
>
> Thanks
> James
>
> Subject: [PATCH 1/1] modpost: fix unwanted VMLINUX_SYMBOL_STR expansion
>
> Commit a4b6a77b77ba4f526392612c2365797fab956014 ("module: fix symbol
> versioning with symbol prefixes") broke the MODVERSIONS loading of any
> module using memcmp (e.g. ipv6) on x86_32, as it's defined to
> __builtin_memcmp which is expanded by VMLINUX_SYMBOL_STR. Use
> __VMLINUX_SYMBOL_STR instead which doesn't expand the argument.
>
> Reported-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> Signed-off-by: James Hogan <james.hogan@...tec.com>
> Cc: Rusty Russell <rusty@...tcorp.com.au>
> Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Cc: H. Peter Anvin <hpa@...or.com>
> ---
>  scripts/mod/modpost.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index 1f90961..a4be8e1 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -1957,7 +1957,7 @@ static int add_versions(struct buffer *b, struct module *mod)
>                                 s->name, mod->name);
>                         continue;
>                 }
> -               buf_printf(b, "\t{ %#8x, VMLINUX_SYMBOL_STR(%s) },\n",
> +               buf_printf(b, "\t{ %#8x, __VMLINUX_SYMBOL_STR(%s) },\n",
>                            s->crc, s->name);
>         }
>
> --
> 1.8.1.2
>



-- 
With Best Regards,
Andy Shevchenko
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