Unable to compile proprietary kernel driver under ARM64 Ubuntu 14.04

[Chuck Tuffli]

Compiling a kernel driver with a proprietary license (i.e. MODULE_LICENSE("Proprietary")) for ARM64 under Ubuntu 14.04 results in the following link error:

# make CROSS_COMPILE=aarch64-linux-gnu- ARCH=arm64 -C /home/ctuffli/dev/ubuntu-trusty/debian/build/build-generic/ M=`pwd` modules
make: Entering directory `/home/ctuffli/dev/ubuntu-trusty/debian/build/build-generic'
  CC [M] /home/ctuffli/dev/ocs/test/test.o
In file included from /home/ctuffli/dev/ubuntu-trusty/include/linux/printk.h:5:0,
                 from /home/ctuffli/dev/ubuntu-trusty/include/linux/kernel.h:13,
                 from /home/ctuffli/dev/ubuntu-trusty/include/linux/sched.h:15,
                 from /home/ctuffli/dev/ubuntu-trusty/arch/arm64/include/asm/compat.h:25,
                 from /home/ctuffli/dev/ubuntu-trusty/arch/arm64/include/asm/stat.h:23,
                 from /home/ctuffli/dev/ubuntu-trusty/include/linux/stat.h:5,
                 from /home/ctuffli/dev/ubuntu-trusty/include/linux/module.h:10,
                 from /home/ctuffli/dev/ocs/test/test.c:1:
/home/ctuffli/dev/ocs/test/test.c: In function ‘__inittest’:
/home/ctuffli/dev/ubuntu-trusty/include/linux/init.h:297:4: warning: return from incompatible pointer type [enabled by default]
  { return initfn; } \
    ^
/home/ctuffli/dev/ocs/test/test.c:34:1: note: in expansion of macro ‘module_init’
 module_init(test_init);
 ^
  Building modules, stage 2.
  MODPOST 1 modules
FATAL: modpost: GPL-incompatible module test.ko uses GPL-only symbol 'xen_dma_ops'
make[3]: *** [__modpost] Error 1
make[2]: *** [modules] Error 2
make[1]: *** [sub-make] Error 2
make: *** [all] Error 2
make: Leaving directory `/home/ctuffli/dev/ubuntu-trusty/debian/build/build-generic'

It appears that including <linux/dma-mapping.h> is enough to trigger this problem
# nm -gl test.o | grep xen_start_info
                 U xen_start_info /home/ctuffli/dev/ubuntu-trusty/arch/arm64/include/asm/dma-mapping.h:42

Test case attached
---
AlsaDevices: Error: command ['ls', '-l', '/dev/snd/'] failed with exit code 2: ls: cannot access /dev/snd/: No such file or directory
AplayDevices: Error: [Errno 2] No such file or directory
ApportVersion: 2.14.1-0ubuntu3.2
Architecture: arm64
ArecordDevices: Error: [Errno 2] No such file or directory
CRDA: Error: [Errno 2] No such file or directory
CurrentDmesg: [ 15.365073] xgene-enet 17020000.ethernet eth0: eth0: link up 1000 Mbps
DistroRelease: Ubuntu 14.04
HibernationDevice: RESUME=UUID=88388f89-d798-4675-9542-27cacae45a9d
IwConfig: Error: [Errno 2] No such file or directory
Lsusb: Error: command ['lsusb'] failed with exit code 1: unable to initialize libusb: -99
Package: linux (not installed)
PciMultimedia:

ProcEnviron:
 TERM=screen
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcFB:

ProcKernelCmdLine: console=ttyS0,115200n8 ro
ProcVersionSignature: Ubuntu 3.13.0-32.57-generic 3.13.11.4
RelatedPackageVersions:
 linux-restricted-modules-3.13.0-32-generic N/A
 linux-backports-modules-3.13.0-32-generic N/A
 linux-firmware 1.127.4
RfKill: Error: [Errno 2] No such file or directory
Tags: trusty
Uname: Linux 3.13.0-32-generic aarch64
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups:

_MarkForUpload: True

[Chuck Tuffli (ctuffli)]

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[Chuck Tuffli (ctuffli)]

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[Chuck Tuffli (ctuffli)]

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[Chuck Tuffli (ctuffli)]

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[Chuck Tuffli (ctuffli)]

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[Chuck Tuffli (ctuffli)]

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[Chuck Tuffli (ctuffli)]

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[Chuck Tuffli (ctuffli)]

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[Chuck Tuffli (ctuffli)]

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[Brad Figg (brad-figg)]

This change was made by a bot.

[Andy Whitcroft (apw)]

You are not permitted to link to GPL only symbols if your module is not GPL, the error there is telling you you are trying to do exactly that:

    FATAL: modpost: GPL-incompatible module test.ko uses GPL-only symbol 'xen_dma_ops'

Either one has to work with the upstream contributor to relax that symbol to EXPORT_SYMBOL, or you need to find an alternative.

If you do not expect your device to encounter systems running on XEN you could likely short circut this by defining xen_dma_ops as NULL. before you include that header:

    #define xen_dma_ops NULL

Though if you do that you should also check for xen_initial_domain() in your init (if you can call that) and abort if true.

That said, it seems rather unfortuanate that those ops being _GPL renders he whole DMA infratructure useless. It is worth approaching whoever committed that and asking for that symbol to be relaxed.

[Andy Whitcroft (apw)]

The dependencies on xen_dma_ops were introduced in the commit below:

  commit c7e9bc548325f19635e7ac7cd5f3ec587228952e
  Author: Stefano Stabellini <email address hidden>
  Date: Fri Oct 18 16:01:26 2013 +0000

    arm/xen: get_dma_ops: return xen_dma_ops if we are running as xen_initial_domain

and the ops themselves in:

  commit 83862ccfc0a03212fde43b4ac29c28381828768b
  Author: Stefano Stabellini <email address hidden>
  Date: Thu Oct 10 13:40:44 2013 +0000

    xen/arm,arm64: enable SWIOTLB_XEN

So at least it seems to be the same person here.