Re: [linux-dvb] Re: Kernel oops with ttusb_dec

[Holger Waechtler <holger@convergence.de>]

Olaf Titz wrote:
> [CCd to linux-kernel and dvb lists. Context: SuSE 9.0, kernel 2.4.21,
> ttusb_dec module fails]
> 
> 
>>>Is cipcb really needed in Release 1.36? It is the only modules which gives
>>>crc32 as a symbol.
> 
> 
>>>>>EIP; dde5ba82 <[cipcb]crc32+12/30>   <=====
>>>>>
>>>>>eax; dea04560 <[ttusb_dec]dsp_dec2000t+0/69100>
>>>>>edx; dea0455f <[ttusb_dec]dec3000s_frontend_info+bf/c0>
>>>>>esi; ddcfde18 <[snd-mixer-oss].data.end+eaf2141/ec4c389>
>>>>>edi; ddcfde20 <[snd-mixer-oss].data.end+eaf2149/ec4c389>
>>>>>esp; ddcfcdb4 <[snd-mixer-oss].data.end+eaf10dd/ec4c389>
> 
> 
>>No, cipcb isn't needed.  It should be using the crc32 function from the main
>>kernel.  If it's trying to use the one in cipcb, which takes very different
>>arguments, it's no wonder there is a problem.
>>
>>I'm unsure of the right way to fix this.  Suggestions anyone?

it's probably safer to use crc32_le() or crc32_be(), depends on which 
one exactly you need.

> Eeek. If the OP didn't even know if he needed the cipcb module, this
> should mean he didn't knowingly start the CIPE driver, and[*] thus the
> cipcb module was loaded by the modprobe dependency mechanism by virtue
> of it defining a symbol called "crc32".
> 
> modprobe shouldn't know of that symbol in the CIPE module at all,
> because it's not meant to be exported. There are some definitions in
> the module subsystem which deal with the exporting of symbols. I
> suspect either CIPE or DVB (or both of them) needs a fix in this area.
> Anyone here knows more?

Use a recent kernel, there crc32(), crc32_le() and crc32_be() are 
implemented as library functions.

> Another data point: crc32 isn't available in 2.4.21 at all, so it's
> apparently(?) not a kernel configuration problem. But shouldn't that
> mean that the ttusb_dec driver wouldn't run at all under that kernel?
> 
> Ah, by the way, this could perhaps have been avoided completely if the
> kernel was compiled with CONFIG_MODVERSIONS enabled (because then the
> crc32 function, if properly exported, would have gotten a name which
> depends on its arguments). This not being on unconditionally is one of
> my pet peeves with Linux and distros, because of the many CIPE
> bugreports I get which are due to just version incompatibilities.

Enabling CONFIG_MODVERSIONS causes even more troubles, just browse the 
LinuxDVB mailing list archives, you'll find hundrets of mails where 
people failed to install standalone drivers just because they/their 
friends/their distributor didn't managed it to install matching kernel 
source, kernel config and kernel image.

Holger