Debian64: "FATAL: modpost: GPL-incompatible module fglrx.ko uses GPL-only symbol '__rcu_read_lock'"

I unpacked the drivers with:

./ati-driver-installer-8.42.3-x86.x86_64.run --extract fglrx

Then in the fglrx/common/lib/modules/fglrx/build_mod directory there are a few files, you need to modify two of them:

drm_compat.h firegl_public.c

In drm_compat.h you need to change:

#define MODULE_LICENSE(x) to #define MODULE_LICENSE("GPL")

and in firegl_public.c you need to change:

MODULE_LICENSE("long license string I can't remember the exact detals of") to MODULE_LICENSE("GPL");

Then run:

./packages/Debian/ati-packager.sh --buildpkg etch

from the top level fglrx directory. Install the generated .deb files which end up in the directory where you first extracted the drivers, with

sudo dpkg -i fglrx*deb

Then:

sudo m-a a-i fglrx

Finally run: sudo aticonfig --initial and reboot. You can then try different options to aticonfig to customise your display but this should be enough to get it working with full 3d acceleration.