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  • HOWTO build additional kernel modules for Android

    https://github.com/marco-pratesi/android/blob/master/HOWTOs/Android-Build-Kernel-Modules-HOWTO.txt


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    1. *************************************************
    2. HOWTO build additional kernel modules for Android
    3. *************************************************

    5. ----------
    6. Disclaimer
    7. ----------

    9. This HOWTO assumes usage of root privileges, i.e. that your device is rooted.
    10. It is also assumed that you are able to use a root shell on a Terminal Emulator
    11. on Android: its usage is implicitly assumed (and is never explicitly cited).
    12. Rooting your Android device might void your warranty, damage it,
    13. kill your cat, burn your house, and cause many other dreadful things.
    14. I do not take any responsibility, you are completely on your own.
    15. If you don't know what "rooting Android" means, this HOWTO is not suited
    16. for you.

    18. -------------------
    19. Scope of this HOWTO
    20. -------------------

    22. So many documents dealing with the Linux kernel compilation for GNU/Linux
    23. are already available.
    24. This document is not intended to write yet another one of them: here, I suppose
    25. that you are already familiar with this topic; if you are not, train yourself
    26. building kernel on GNU/Linux before (it is a good idea anyway :-) ).
    27. There are some documents about cross-compilation of the Linux kernel
    28. for Android, too; I prepared this HOWTO to collect and organize informations
    29. relevant to my needs and to support other HOWTOs I want to write.
    30. This HOWTO also discusses *native* build of kernel modules for Android;
    31. to the best of my knowledge, at the time of this writing, this is the only
    32. document facing this topic.

    34. --------------
    35. Test platforms
    36. --------------

    38. Tested, not exhaustively, using the following build platforms:
    39. - GNU/Linux Ubuntu 12.04 x86 (32 bit)
    40. - GNU/Linux Ubuntu 14.04 x86_64 (64 bit).

    42. Tested on a Google Nexus 7 3G 2012 tablet, with
    43. - Cyanogenmod 10.1.3
    44. - Cyanogenmod 10.2.1
    45. I made only few tests on 10.2.1, as I experienced some problems
    46. with CTRL and cursor arrows on the Android Terminal Emulator
    47. (both with the virtual keyboard and with an external USB keyboard),
    48. and I was not comfortable with some behaviors of the default shell.
    49. Do not blame me as a newbie: I performed wipings and factory reset more than
    50. once, but such annoying behaviors persisted, and I can not tolerate being
    51. uncomfortable with the only true user interface, i.e. the shell terminal. :-)
    52. Then I went back to 10.1.3 and carried out all the work on it.

    54. ------------------------
    55. Get Linux kernel sources
    56. ------------------------

    58. Download the kernel source tree that has been used to build the kernel
    59. running on your mobile device.
    60. Some relevant repositories may be:
    61. https://android.googlesource.com/
    62. https://github.com/cyanogenmod/
    63. If such sources are either not available or packed without documentation
    64. (and you do not have a crystal ball to guess how to compile them),
    65. search for the kernel source tree that most closely matches your case.

    67. As an example, kernel sources of Cyanogenmod for the Google Nexus 7 2012,
    68. both for the Wi-Fi version (codename: grouper) and the 3G version
    69. (codename: tilapia), can be found [1] at
    70. https://github.com/cyanogenmod/android_kernel_asus_grouper/ =>
    71. https://github.com/cyanogenmod/android_kernel_asus_grouper/tree/cm-10.1
    72. https://github.com/cyanogenmod/android_kernel_asus_grouper/tree/cm-10.2
    73. [...]

    75. Hint: download a zip/tar.gz archive through the web page of the repository,
    76. to save a lot of time and bandwidth; cloning through the git client,
    77. you would download the .git directory, too, that takes a lot of disk space
    78. and bandwidth, and is only needed for more advanced usage of the repository.
    79. The same suggestion may be useful for suubsequent sections of this document.

    81. ------------------------------------------------------
    82. Choose a toolchain to cross-compile the kernel sources
    83. (or use a native compiler, if you are brave enough)
    84. ------------------------------------------------------

    86. The best option for compatibility: if it is possible (if it is available),
    87. choose the same toolchain that has been used to build the kernel
    88. of your Android distribution.
    89. As you can experience on GNU/Linux, this option is not a must, but minimizes
    90. the risk of binary incompatibilities.

    92. Some available toolchains:

    94. - the prebuilt gcc on android.googlesource.com [2]
    95.   (for 64 bit build platforms only)
    96.   https://android.googlesource.com/platform/prebuilts/gcc/linux-x86/arm/arm-eabi-4.6 =>
    97.   https://android.googlesource.com/platform/prebuilts/gcc/linux-x86/arm/arm-eabi-4.6/+/master =>
    98.   https://android.googlesource.com/platform/prebuilts/gcc/linux-x86/arm/arm-eabi-4.6/+archive/master.tar.gz

    100. - the Cyanogenmod prebuilt toolchain [1] (for 32 bit build platforms;
    101.   installation of some 32 bit libraries is needed on 64 bit build platforms)
    102.   https://github.com/CyanogenMod/android_prebuilt.git =>
    103.   https://github.com/CyanogenMod/android_prebuilt =>
    104.   https://github.com/CyanogenMod/android_prebuilt/tree/cm-10.1 =>
    105.   https://github.com/CyanogenMod/android_prebuilt/archive/cm-10.1.zip
    106.   https://github.com/CyanogenMod/android_prebuilt/tree/cm-10.2 =>
    107.   https://github.com/CyanogenMod/android_prebuilt/archive/cm-10.2.zip
    108.   [...]

    110. - the Android Native Development Kit (NDK) [3]

    112. Install (i.e. unpack) the toolchain(s) in the directory you prefer.

    114. Alternatively, you can build your modules just on your mobile device,
    115. using a native compiler [8] instead of a cross-compiler.
    116. This option is discussed at the end of this document.

    118. ----------------------------------------------------
    119. Set environment variables according to the toolchain
    120. ----------------------------------------------------

    122. For all toolchains:
    123. export ARCH=arm
    124. export SUBARCH=arm

    126. For the android.googlesource.com prebuilt gcc:
    127. export PATH=[your_installation_path]/bin:$PATH
    128. (as an example:
    129.  export PATH=/opt/android.googlesource.com/platform/prebuilts/gcc/linux-x86/arm/arm-eabi-4.6/bin:$PATH
    130. )
    131. export CROSS_COMPILE=arm-eabi-

    133. For the Cyanogenmod prebuilt toolchain:
    134. export PATH=[your_installation_path]/linux-x86/toolchain/arm-eabi-4.4.3/bin:$PATH
    135. (as an example:
    136.  export PATH=/opt/android_prebuilt-cm-10.1/linux-x86/toolchain/arm-eabi-4.4.3/bin:$PATH
    137. )
    138. export CROSS_COMPILE=arm-eabi-

    140. For Android NDK:
    141. set the PATH environment variable according to
    142. - usage of either a 32 bit or a 64 bit build platform
    143. - your installation path of the Android NDK
    144. - the cross-compiler version you want to use
    145. as an example:
    146. export PATH=/opt/android-ndk-r9d/toolchains/arm-linux-androideabi-4.6/prebuilt/linux-x86_64/bin:$PATH
    147. export CROSS_COMPILE=arm-linux-androideabi-

    149. For another toolchain:
    150. search for the documentation of that toolchain :-)
    151. Very likely, the directory to prepend to the PATH environment variable
    152. is the [...]/bin directory where you find many gcc executables named
    153. [NAME_PREFIX]addr2line
    154. [NAME_PREFIX]ar
    155. [NAME_PREFIX]as
    156. [NAME_PREFIX]c++
    157. [NAME_PREFIX]c++filt
    158. [NAME_PREFIX]cpp
    159. [NAME_PREFIX]g++
    160. [NAME_PREFIX]gcc
    161. [NAME_PREFIX]gcov
    162. [NAME_PREFIX]gdb
    163. [NAME_PREFIX]gprof
    164. [NAME_PREFIX]ld
    165. [NAME_PREFIX]nm
    166. [NAME_PREFIX]objcopy
    167. [NAME_PREFIX]objdump
    168. [NAME_PREFIX]ranlib
    169. [NAME_PREFIX]readelf
    170. [NAME_PREFIX]size
    171. [NAME_PREFIX]strings
    172. [NAME_PREFIX]strip
    173. [NAME_PREFIX]...
    174. ([NAME_PREFIX] is very likely something as "arm-eabi-",
    175. "arm-linux-androideabi-", and so on)
    176. then, after the PATH environment variable, set
    177. export CROSS_COMPILE=[NAME_PREFIX]
    178. and then hope for the best and try :-)

    180. ---------------------------------
    181. Build the needed kernel module(s)
    182. ---------------------------------

    184. Unpack the kernel sources and cd to their tree.
    185. Example:
    186. unzip android_kernel_asus_grouper-cm-10.1.zip
    187. cd android_kernel_asus_grouper-cm-10.1

    189. The kernel may refuse loading modules if the vermagic does not match,
    190. thus edit the Makefile to set KERNELRELEASE just according to it [1].
    191. To find the exact target kernel version string, you may either run
    192. "uname -a" / "cat /proc/version" on a shell terminal (Android Terminal
    193. Emulator / ADB shell / ...), or look for informations about the system
    194. (Kernel version) in the Setting GUI/Application.
    195. Examples about Google Nexus 7 2012 GSM (tilapia):
    196. Settings => About tablet => Kernel version:
    197. CM-10.1.3: 3.1.10-gd08812a build03@cyanogenmod #1 Mod Sep 23 20:47:32 PDT 2013
    198. CM-10.2.1: 3.1.10-g30c5396 build02@cyanogenmod #1 Mon Feb 3 16:09:59 PST 2014
    199. $ uname -a
    200. CM-10.1.3: Linux localhost 3.1.10-gd08812a #1 SMP PREEMPT Mon Sep 23 20:47:32 PDT 2013 armv7l GNU/Linux
    201. CM-10.2.1: Linux localhost 3.1.10-g30c5396 #1 SMP PREEMPT Mon Feb 3 16:09:59 PST 2014 armv7l GNU/Linux
    202. diff Makefile.old Makefile # for CM-10.1.3:
    203. 380c380
    204. < KERNELRELEASE = $(shell cat include/config/kernel.release 2> /dev/null)
    205. ---
    206. > KERNELRELEASE = "3.1.10-gd08812a"
    207. Alternatively, you may edit include/config/kernel.release accordingly
    208. (if it exists).
    209. NOTE: in more complex cases, you may have to also edit include/linux/vermagic.h
    210. and some other similar stuff, eventually after some subsequent steps.

    212. Choose a config to start with - if possible, just the one matching the kernel
    213. you are currently running on your mobile device - and copy it as .config
    214. in the kernel sources tree.
    215. Example:
    216. cp arch/arm/configs/cyanogenmod_grouper_defconfig .config

    218. NOTE: check if loadable module support is enabled ("CONFIG_MODULES=y").
    219. If it is not, to add hardware support, rebuilding and reinstalling
    220. (i.e. reflashing) the whole kernel is needed anyway:
    221. - if you want to use modules, you have to build a kernel with loadable module
    222.   support enabled
    223. - if you decide to choose the static option, without loadable module support,
    224.   to change the set of supported hardware you need to rebuild and reinstall
    225.   the whole kernel each time anyway.
    226. As an example, loadable module support is disabled on Cyanogenmod
    227. for the Google Nexus 7 2013 tablet and for the Google Nexus 4 smartphone:
    228. "# CONFIG_MODULES is not set" in
    229. https://github.com/CyanogenMod/android_kernel_google_msm/blob/cm-10.2/arch/arm/configs/cyanogen_flo_defconfig
    230. https://github.com/CyanogenMod/android_kernel_google_msm/blob/cm-10.2/arch/arm/configs/cyanogen_mako_defconfig
    231. https://github.com/CyanogenMod/android_kernel_google_msm/blob/cm-11.0/arch/arm/configs/cyanogen_flo_defconfig
    232. https://github.com/CyanogenMod/android_kernel_google_msm/blob/cm-11.0/arch/arm/configs/cyanogen_mako_defconfig

    234. Manipulate .config as it is usually done on GNU/Linux: after all, you are
    235. dealing with the Linux kernel anyway, even though
    236. - you are *cross*-compiling it
    237. - your target platform is Android/Linux instead of GNU/Linux

    239. Even though you are cross-compiling, you can also use "make menuconfig":
    240. as an example, to build the ftdi_sio.ko and mcs7830.ko modules:

    242. Device Drivers ---> USB support --->
    243.                     ^^^^^^^^^^^^^^^^ check that host-side and OTG support are enabled...
    244.                     ^^^^^^^^^^^^^^^^ very interesting: USB Gadget Support (http://www.linux-usb.org/gadget)
    245. *** USB port drivers ***
    246. USB Serial Converter support --->
    247. <M> USB FTDI Single Port Serial Driver (CONFIG_USB_SERIAL_FTDI_SIO)

    249. Device Drivers ---> Network device support ---> USB Network Adapters --->
    250. <M> MosChip MCS7830 based Ethernet adapters

    252. However, a quicker (if appropriate) solution consists of editing .config
    253. with bare hands:
    254. cp .config .config.old
    255. edit .config with a text editor, according to the following diff:
    256. diff .config.old .config
    257. 1267c1267
    258. < # CONFIG_USB_NET_MCS7830 is not set
    259. ---
    260. > CONFIG_USB_NET_MCS7830=m
    261. 2457c2457
    262. < # CONFIG_USB_SERIAL_FTDI_SIO is not set
    263. ---
    264. > CONFIG_USB_SERIAL_FTDI_SIO=m

    266. Prepare for build using the provided .config [4], [5]:
    267. make oldconfig
    268. make prepare
    269. make modules_prepare
    270. (For further options, run "make help".)

    272. Build the needed modules; you do not have to build everything, you can avoid
    273. building the static part of the kernel and unneeded (already installed)
    274. modules [5], [6]:
    275. make M=[directory of the module to build]
    276. Examples:
    277. make M=drivers/usb/serial/ # to build drivers/usb/serial/ftdi_sio.ko
    278. make M=drivers/net/usb/ # to build drivers/net/usb/mcs7830.ko
    279. (You may want to run "make" with the -j option to set the number of CPU
    280. cores to be used on the build platform [1], e.g. "make -j2 ..." on a dual-core
    281. netbook; anyway, if you only have to build a few modules, this option
    282. is almost insignificant.)

    284. NOTE: Cyanogenmod 10.1.3 and 10.2.1 did not load modules I built
    285. with Android NDK; the following error messages were provided:
    286. ------------------------------
    287. # insmod ftdi_sio.ko
    288. insmod: can't insert 'ftdi_sio.ko': invalid module format
    289. # dmesg | tail
    290. [...]
    291. [...] ftdi_sio: unknown relocation: 27
    292. ------------------------------
    293. The CFLAGS_MODULE=-fno-pic option solved the problem [7]:
    294. make CFLAGS_MODULE=-fno-pic M=drivers/usb/serial/
    295. make CFLAGS_MODULE=-fno-pic M=drivers/net/usb/

    297. Strip modules to remove unneded symbols and save memory on the target device
    298. that will run them:
    299. ${CROSS_COMPILE}strip --strip-debug [path]/[just_built_module].ko
    300. Example:
    301. ls -l drivers/usb/serial/ftdi_sio.ko # about 300 kbytes before stripping it
    302. ${CROSS_COMPILE}strip --strip-debug drivers/usb/serial/ftdi_sio.ko
    303. ls -l drivers/usb/serial/ftdi_sio.ko # about 100 kbytes after stripping it
    304. ls -l drivers/net/usb/mcs7830.ko # about 200 kbytes before stripping it
    305. ${CROSS_COMPILE}strip --strip-debug drivers/net/usb/mcs7830.ko
    306. ls -l drivers/net/usb/mcs7830.ko # about 10 kbytes after stripping it

    308. Through a program capable of viewing/editing binary files (e.g. VIM),
    309. open a .ko module in the target system (very likely, in /system/lib/modules)
    310. and the built module(s), to check whether "vermagic=..." is the same;
    311. if it is not and the built modules do not load, go back and try again,
    312. changing something accordingly in your build process.

    314. --------------------
    315. Test built module(s)
    316. --------------------

    318. After building a kernel module, you can put it the /data/local directory
    319. (or in /sdcard, or somewhere else) of the target Android device.
    320. The system directory for kernel modules is very likely /system/lib/modules;
    321. I do not suggest using it: apart from the fact that you have to remount
    322. /system as read-write to add/remove files to /system/lib/modules,
    323. custom built modules are more easily identified if you put them elsewhere.
    324. One uploaded a module to the target system, try to load it into
    325. the running kernel: as an example,
    326. insmod /data/local/ftdi_sio.ko
    327. If no errors are reported, check if the module has been loaded:
    328. lsmod | grep ftdi_sio

    330. If something went wrong, try the following commands to investigate:
    331. insmod /data/local/ftdi_sio.ko ; dmesg
    332. insmod /data/local/ftdi_sio.ko ; dmesg | grep ftdi
    333. and then search the web for the problem you are experiencing; an exhaustive
    334. discussion of all possible cases is not possible, you mileage may vary,
    335. I can only wish you good luck :-)

    337. --------------------------------------------------
    338. HOWTO build your modules through a native compiler
    339. --------------------------------------------------

    341. You can build your modules just on your mobile device using a native
    342. compiler, whose installation is discussed in [8], i.e. you can natively
    343. build your modules just on your (target) mobile device, instead of
    344. cross compiling them.

    346. First step: build and install a native compiler as discussed in [8].
    347. Yes, you need a cross-compiler - namely Android NDK - to build your
    348. native compiler :-D but you need it only once: subsequently, you can use
    349. the native compiler to build your stuff :-)

    351. Then follow the steps discussed in this document, skipping what is
    352. related to cross-build.
    353. Briefly: unpack your kernel sources, edit the Makefile, prepare your .config,
    354. make your modules, strip them.
    355. Some simple tricks are needed to solve some minor problems, as discusses
    356. in the following.

    358. *** 1 ***

    360. "make modules_prepare" fails, because the "elf.h" available in Android NDK
    361. (i.e. the one used by the native compiler [8]) is not enough.
    362. To overcome this problem, copy in the scripts/mod/ directory of the kernel
    363. sources tree the "elf.h" available in Glibc.
    364. You can easily find it: you can just copy /usr/include/elf.h from a GNU/Linux
    365. installation (I used the one available in GNU/Linux Ubuntu 14.04 x86_64).
    366. Edit scripts/mod/elf.h to remove inclusion of <bits/auxv.h>, as it is
    367. not available in Android NDK and is not needed:
    368. diff -up scripts/mod/elf.h.orig scripts/mod/elf.h
    369. ------------------------------
    370. --- scripts/mod/elf.h.orig
    371. +++ scripts/mod/elf.h
    372. @@ -972,7 +972,7 @@
    373.      } a_un;
    374.  } Elf64_auxv_t;

    376. -#include <bits/auxv.h>
    377. +//#include <bits/auxv.h>
    378.  /* Note section contents. Each entry in the note section begins with
    379.     a header of a fixed form. */

    381. ------------------------------

    383. Then edit scripts/mod/modpost.h to include just scripts/mod/elf.h:
    384. diff -up scripts/mod/modpost.h.orig scripts/mod/modpost.h
    385. ------------------------------
    386. --- scripts/mod/modpost.h.orig
    387. +++ scripts/mod/modpost.h
    388. @@ -7,7 +7,7 @@
    389.  #include <sys/mman.h>
    390.  #include <fcntl.h>
    391.  #include <unistd.h>
    392. -#include <elf.h>
    393. +#include "elf.h"

    395.  #include "elfconfig.h"

    397. ------------------------------

    399. *** 2 ***

    401. Just as for cross-compilation of modules through Android NDK,
    402. the CFLAGS_MODULE=-fno-pic may be needed to avoid relocation errors
    403. when loading the modules [7]: as an example,
    404. make CFLAGS_MODULE=-fno-pic M=drivers/usb/serial/
    405. make CFLAGS_MODULE=-fno-pic M=drivers/net/usb/

    407. *** 3 ***

    409. "make menuconfig" and "make nconfig" fail if ncurses headers are not found,
    410. i.e. if they are either not available or installed in a "non-standard"
    411. directory; to solve this problem, edit scripts/kconfig/Makefile to add
    412. an include path: as an example,
    413. diff -up scripts/kconfig/Makefile.orig scripts/kconfig/Makefile
    414. ------------------------------
    415. --- scripts/kconfig/Makefile.orig
    416. +++ scripts/kconfig/Makefile
    417. @@ -147,7 +147,7 @@
    418.  # Use recursively expanded variables so we do not call gcc unless
    419.  # we really need to do so. (Do not call gcc as part of make mrproper)
    420.  HOST_EXTRACFLAGS += $(shell $(CONFIG_SHELL) $(check-lxdialog) -ccflags)
    421. - -DLOCALE
    422. + -DLOCALE -I/data/local/include/ncurses

    424.  # ===========================================================================
    425.  # Shared Makefile for the various kconfig executables:
    426. ------------------------------
    427. where /data/local/include/ncurses is the directory containing curses.h

    429. I successfully used "make menuconfig" and "make nconfig" both via the ADB shell
    430. and on the Android Terminal Emulator, but please note that your terminal
    431. must provide at least
    432. - 19 lines by 80 columns to run "make menuconfig"
    433. - 20 lines and 75 columns to run "make nconfig"
    434. hence you may have to set small fonts on the Android Terminal Emulator,
    435. especially if the screen must provide room for the virtual keyboard, too.
    436. Via ADB, I experienced some "refresh" problems with "make menuconfig",
    437. however they can be almost completely solved through a suited setting
    438. of the TERM environment variable and they do not prevent usage of the tool.

    440. ----------
    441. References
    442. ----------

    444. [1] http://mehrvarz.github.io/building-nexus-7-kernel/
    445. [2] http://source.android.com/source/building-kernels.html
    446. [3] https://developer.android.com/tools/sdk/ndk/index.html
    447. [4] http://www.pixelbeat.org/docs/rebuild_kernel_module.html
    448. [5] http://askubuntu.com/questions/168279/how-do-i-build-a-single-in-tree-kernel-module
    449. [6] http://www.linuxquestions.org/questions/linux-kernel-70/rebuilding-a-single-kernel-module-595116/#post3648679
    450. [7] http://stackoverflow.com/questions/11614441/hello-world-kernel-module-for-android-unknown-relocation-27-when-insmod
    451. [8] https://github.com/marco-pratesi/android/tree/master/gcc_and_friends


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