linux-kernel - Re: [crash] af9005_usb_module_init(): BUG: unable to handle kernel paging request at ff100000

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Date:	Wed, 04 Feb 2009 08:12:18 -0800
From:	Daniel Walker <dwalker@...o99.com>
To:	Luca Olivetti <luca@...toso.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Greg KH <gregkh@...e.de>,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	linux-kernel@...r.kernel.org, Hans Verkuil <hverkuil@...all.nl>,
	Janne Grunau <janne-dvb@...nau.be>
Subject: Re: [crash] af9005_usb_module_init(): BUG: unable to handle kernel
	paging request at ff100000

On Wed, 2009-02-04 at 16:49 +0100, Luca Olivetti wrote:
> 
> No, I havent: the source file isn't compiled, so those symbols are 
> unavailable to the linker.
> The only reference I could find (well, I haven't searched that much) on 
> the expected behaviour of the linker when a weak attribute is not found 
> is this:
> 
> http://software.intel.com/en-us/articles/software-convention-models-using-elf-visibility-attributes/
> 
> "# STB_WEAK. A weak symbol behaves as does a global symbol, with a few 
> differences. If there are both a weak and a global definition of a name, 
> the global definition takes precedence and any weak definitions are 
> ignored. The Linker will not extract archive members to resolve 
> undefined weak symbols. It is not an error to have unresolved weak 
> references; unresolved weak symbols have the value zero. "

I wrote a little test to see if this was true in gcc, and it does appear
to give a NULL in a simple case. However, after reviewing Ingo's
disassmbled function it look like the crash is happening on this line,

/* module stuff */
static int __init af9005_usb_module_init(void)
{
        int result;
        if ((result = usb_register(&af9005_usb_driver))) {
                err("usb_register failed. (%d)", result);
                return result;
        }
        rc_decode = symbol_request(af9005_rc_decode);
        rc_keys = symbol_request(af9005_rc_keys);
        rc_keys_size = symbol_request(af9005_rc_keys_size);
        if (rc_decode == NULL || rc_keys == NULL || rc_keys_size == NULL) {
                err("af9005_rc_decode function not found, disabling remote");
                af9005_properties.rc_query = NULL;
        } else {
                af9005_properties.rc_key_map = rc_keys;
                af9005_properties.rc_key_map_size = *rc_keys_size; /* <= crash !!! */
        }

        return 0;
}

That line should never run if everything is NULL ..

Daniel

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