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Old 11-14-2004, 09:41 AM   #1
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Registered: Nov 2004
Location: Somerville, MA, USA
Distribution: Debian "woody"
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Question user-mode Linux char device driver with "unresolved symbol __generic_copy_to_user"

I am writing a device driver for a university course. The driver does not do anything especially useful- it simply reads messages when a user writes to the devices, and sends the messages back when a user writes from the device. The device is somewhat similar to the "scull" device in the O'Reilly _Linux Device Drivers_ book, albeit much less complicated.

I'm trying to test this module using user-mode Linux, which was provided by the professor in our course. The UML version is Debian, kernel 2.4.20-8um, running on an i686. I'm compiling the module like so:

gcc -D__KERNEL__ -I/usr/share/include -Wall -Wstrict-prototypes \
-Wno-trigraphs -O2 -fno-strict-aliasing -fno-common \
-fomit-frame-pointer -pipe -mpreferred-stack-boundary=2 \
-march=i686 -DMODULE -nostdinc -iwithprefix include \
-c $1

This command line *should* include all the necessary flags for user-mode Linux. I'm compiling outside of UML, in the regular Debian distribution that the machine is running. The program compiles with no errors and no warnings. However, when I try to load it into UML via insmod, I get the following error:

(none):~# /sbin/insmod -f csmail.o
csmail.o: unresolved symbol __generic_copy_from_user
csmail.o: unresolved symbol __generic_copy_to_user
Hint: You are trying to load a module without a GPL compatible license
and it has unresolved symbols. Contact the module supplier for
assistance, only they can help you.

The weird thing is that this error does *not* happen when I install the module on my Debian system at work. However, I can't debug on my work machine, because a bug somewhere in my code causes the whole system to crash when I write to the device (I suspect it's a null pointer somewhere.) My goal is to just get the code loaded into UML, so that I can start debugging it. If anyone has an idea of what might be wrong here, I'd welcome some assistance.

Thank you!



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