[parisc-linux] Module Relocation Problem

[parisc-linux] Module Relocation Problem

[Kai Holthaus]

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Hi,

I'm trying to compile and install the qc-usb (http://qce-ga.sourceforge.net/) 
kernel module on my A5005X server. Compilation works just fine (make all && 
make install), but upon insmodding I get the following error:

Module quickcam, symbol qc_proc_init is out of range for PCREL22F relocation
FATAL: Error inserting quickcam (/lib/modules/2.6.16-pa11/misc/quickcam.ko): 
Invalid module format

I've searched on google (in general) and on this mailing list for help on this 
topic, but couldn't find anything that would help me out, since I'm not 
really a kernel and/or gcc wiz. 

What am I doing wrong? Or is there something in the module code that's not 
compatible with a 64bit hppa kernel?

Thanks so much,

	Kai
-- 
Hofstadter's Law:
  "It always takes longer than you expect,
   even when you take into account Hofstadter's Law."
                             -- Douglas R. Hofstadter

kmh.AT.sonic.net

Check out Mission Octagon - a new, exciting novel!
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Re: [parisc-linux] Module Relocation Problem

[John David Anglin]

> Module quickcam, symbol qc_proc_init is out of range for PCREL22F relocation
> =46ATAL: Error inserting quickcam (/lib/modules/2.6.16-pa11/misc/quickcam.k=
> o):=20

I believe that this has come up before.  The out of range
PCREL22F relocation implies that the module has a "b,l" instruction
(call) whose target can't be reached.  The maximum branch distance
for the "b,l" instruction is ~ 8 MB, so the module must be quite
large.

You might explore ways to reduce the modules's (e.g., limit inlining).
You might also try compiling with the -mlong-calls options.  This forces
GCC to use the "bve" instruction for calls in PA 2.0 compilations.  The
call setup using bve is slightly longer but there are no distance
limitations.  There's also a PA 1.x variant using "ble".  What's unclear
to me is whether the kernel loader has support for the relocations used
in these sequences.

Dave
-- 
J. David Anglin                                  dave.anglin@nrc-cnrc.gc.ca
National Research Council of Canada              (613) 990-0752 (FAX: 952-6602)
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Re: [parisc-linux] Module Relocation Problem

[John David Anglin]

> You might explore ways to reduce the modules's (e.g., limit inlining).
> You might also try compiling with the -mlong-calls options.  This forces
> GCC to use the "bve" instruction for calls in PA 2.0 compilations.  The
> call setup using bve is slightly longer but there are no distance
> limitations.  There's also a PA 1.x variant using "ble".  What's unclear
> to me is whether the kernel loader has support for the relocations used
> in these sequences.

Just thinking, the problem might be going the other way.  If so, reorganzing
the sections used for functions called from the kernel might help.

Dave
-- 
J. David Anglin                                  dave.anglin@nrc-cnrc.gc.ca
National Research Council of Canada              (613) 990-0752 (FAX: 952-6602)
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Re: [parisc-linux] Module Relocation Problem

[Kai Holthaus]

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> You might explore ways to reduce the modules's (e.g., limit inlining).
> You might also try compiling with the -mlong-calls options.  This forces
> GCC to use the "bve" instruction for calls in PA 2.0 compilations.  The
> call setup using bve is slightly longer but there are no distance
> limitations.  There's also a PA 1.x variant using "ble".  What's unclear
> to me is whether the kernel loader has support for the relocations used
> in these sequences.

I think I'm clearly out of my league here, since I honestly don't understand 
bve vs ble... :(

Anyway - I tried compiling the module with the "-mlong-calls" option - now I 
get a different error message upon trying to insert the module into the 
kernel:
	module quickcam: Unknown relocation: 10

Does that tell you anything? Because I have no clue...

Thanks so much for your help!

	Kai

-- 
Hofstadter's Law:
  "It always takes longer than you expect,
   even when you take into account Hofstadter's Law."
                             -- Douglas R. Hofstadter

kmh.AT.sonic.net

Check out Mission Octagon - a new, exciting novel!
http://www.missionoctagon.com

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Re: [parisc-linux] Module Relocation Problem

[John David Anglin]

> Anyway - I tried compiling the module with the "-mlong-calls" option - now =
> I=20
> get a different error message upon trying to insert the module into the=20
> kernel:
> 	module quickcam: Unknown relocation: 10

That's R_PARISC_PCREL21L.  I was afraid this might happen.

About the only easy things are "-Os" and "-fno-inline-functions".
These might shrink the module a bit.  Oh, "-fno-unroll-loops" might
also help.

Dave
-- 
J. David Anglin                                  dave.anglin@nrc-cnrc.gc.ca
National Research Council of Canada              (613) 990-0752 (FAX: 952-6602)
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Re: [parisc-linux] Module Relocation Problem

[Kai Holthaus]

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> That's R_PARISC_PCREL21L.  I was afraid this might happen.
>
> About the only easy things are "-Os" and "-fno-inline-functions".
> These might shrink the module a bit.  Oh, "-fno-unroll-loops" might
> also help.

Thanks again for your help - and unfortunately these didn't do the trick, 
either - same results.

Looking over your earlier reply, you indicated that the module must be 
quite "large" - do you mean file size of the .ko file?
Because that is way under the 8MB you mentioned - the file is around 200kB in 
size...

The qc-usb module is a driver for Logitech's QuickCam Express cameras, which 
are using the kernel usb and video4linux drivers...

Thanks again,

	Kai

-- 
Hofstadter's Law:
  "It always takes longer than you expect,
   even when you take into account Hofstadter's Law."
                             -- Douglas R. Hofstadter

kmh.AT.sonic.net

Check out Mission Octagon - a new, exciting novel!
http://www.missionoctagon.com

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Re: [parisc-linux] Module Relocation Problem

[John David Anglin]

> Looking over your earlier reply, you indicated that the module must be=20
> quite "large" - do you mean file size of the .ko file?
> Because that is way under the 8MB you mentioned - the file is around 200kB =
> in=20
> size...

I wonder if that implies a bug a bug in the kernel loader.  I could
see a problem with PCREL17F relocations with files around 200kB.
These are used with the PA 1.x "bl" instruction.  The range for
"bl" instructions is about +/- 262kB.  The range for the 22F "b,l"
instruction is 32 times larger.

Dave
-- 
J. David Anglin                                  dave.anglin@nrc-cnrc.gc.ca
National Research Council of Canada              (613) 990-0752 (FAX: 952-6602)
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Re: [parisc-linux] Module Relocation Problem

[Thibaut VARENE]

On 6/6/06, John David Anglin <dave@hiauly1.hia.nrc.ca> wrote:
> > Looking over your earlier reply, you indicated that the module must be=20
> > quite "large" - do you mean file size of the .ko file?
> > Because that is way under the 8MB you mentioned - the file is around 200kB =
> > in=20
> > size...
>
> I wonder if that implies a bug a bug in the kernel loader.  I could
> see a problem with PCREL17F relocations with files around 200kB.
> These are used with the PA 1.x "bl" instruction.  The range for
> "bl" instructions is about +/- 262kB.  The range for the 22F "b,l"
> instruction is 32 times larger.

A number of kernel modules fail to load nowadays on parisc. That
includes xfs, netfilter, ipv6... Some are known bloated big ones, but
others are quite surprising. In any case that's clearly a problem we
want to fix at some point.

I remember Randolph saying that might indeed be a kernel loader
issue... Randolph, any thought?

HTH

T-Bone

-- 
Thibaut VARENE
http://www.parisc-linux.org/~varenet/
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Re: [parisc-linux] Module Relocation Problem

[Randolph Chung]

> A number of kernel modules fail to load nowadays on parisc. That
> includes xfs, netfilter, ipv6... Some are known bloated big ones, but
> others are quite surprising. In any case that's clearly a problem we
> want to fix at some point.
> 
> I remember Randolph saying that might indeed be a kernel loader
> issue... Randolph, any thought?

ok, several things:

- I looked at fixing this in binutils, which is really the "right" place
to fix this; unfortunately the changes required are very extensive, so I
gave up

- I looked at using -mlong-calls to address this issue. I've added the
missing relocation that was reported in a previous message on this
thread, but there are other problems - with modules compiled with
-mlong-call I am seeing rather bizarre crashes that I have not had time
to debug further. I do not yet know why they are happening, although I
suspect it has to do with bve clobbering r31. I'm not yet sure if this
is a kernel problem or a gcc problem.

- As to "small" modules causing the out of bounds problem - I haven't
really looked at any modules other than ipv6. If there's a particular
one that is "surprising", I can take a look. Usually it's quite obvious
where the out of bounds problem is.

- As an aside, while looking at the module loading problem, I've
convinced myself that the 64-bit module loader is wrong. OTOH, it seems
to work in most cases, so there's clearly something that I don't yet
understand.....

The module loader has a hard coded limit for the number of GOT entries.
We can exceed this rather easily in some cases when we are using long calls.

randolph
-- 
Randolph Chung
Debian GNU/Linux Developer, hppa/ia64 ports
http://www.tausq.org/
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Re: [parisc-linux] Module Relocation Problem

[James Bottomley]

On Wed, 2006-06-14 at 16:02 +0800, Randolph Chung wrote:
> - As an aside, while looking at the module loading problem, I've
> convinced myself that the 64-bit module loader is wrong. OTOH, it
> seems
> to work in most cases, so there's clearly something that I don't yet
> understand.....

Well ... OK ... since I made that work I can try to remember how I did
it ... what seems to be the problem?

James


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Re: [parisc-linux] Module Relocation Problem

[Kai Holthaus]

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>     1. How do I compile the qc-usb driver directly into the kernel rather
> than as a standalone module?
>
>        At the moment, it is not possible without a lot of work to build the
> qc-usb driver into the kernel. We recommend building qc-usb driver as a
> separate module rather than directly into the kernel. [snip]
>
> So apparently there is a few chance but regarding the generic advise it
> could be out dated, the best is certainly to contact developers to get an
> actual status ;-)

Thanks for the help and advice - here's the answer from the developer:

"I haven't tried doing this recently. I made a couple of attempts to
shoehorn the driver into the kernel build system, but it ended up being
a rathole I didn't want to go down until I've cleaned up the driver
itself. Integrating the qc-usb driver into the kernel is definitely on
the TODO list, just not right now. Sorry."

> Appology if I don't have much more help to offer (no hardware and mainly
> dramaticaly lakes of time, specialy for the moment).

This has all been very helpful. If it is indeed a problem in the hppa-linux 
kernel, I'll keep a watchful eye out for fixes. If there's anything a kernel 
layman like me can do, please let me know.

Thanks,

	Kai

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Re: [parisc-linux] Module Relocation Problem

[Kyle McMartin]

On Sun, Jun 25, 2006 at 07:02:04PM -0700, Kai Holthaus wrote:
> This has all been very helpful. If it is indeed a problem in the hppa-linux 
> kernel, I'll keep a watchful eye out for fixes. If there's anything a kernel 
> layman like me can do, please let me know.
> 

Ironic that you mentioned this today. The fix to module.c James
committed yesterday should fix this for you. Please try 2.6.17-pa6 and
see if that helps.

Cheers,
	Kyle M.
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Re: [parisc-linux] Module Relocation Problem

[Kyle McMartin]

On Sun, Jun 25, 2006 at 09:24:57PM -0700, Kai Holthaus wrote:
> Jun 25 21:20:02 obelix kernel: ioctl32(qcset:2965): Unknown cmd fd(3) 
> cmd(403c7601){00} arg(c05cd808) on /dev/video0
> 

On a first look, it sounds like the driver is not properly handling
compat_ioctl (32bit ioctls on a 64bit kernel).

I can try to take a look sometime this week, unless someone else
beats me to it.

Cheers,
	Kyle
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