This post was written as I attempted to create a kernel module for BeagleBone. The contents includes my troubleshooting efforts and a final resolution as to the method I found which worked, found at the end of the post.<\/p>\n
Here’s what I started with: To get the Angstrom kernel source, I followed the instructions from Angstrom<\/a>, plus some hints from the beaglebone specific page<\/a>.<\/p>\n On that last step, building the kernel, I ran into an issue:<\/p>\n I had started out with only 512MB RAM, being that I only have 2GB on the host machine. I tried upping it to 1GB for the virtual machine, but no dice. Last RAM modification attempt, 2 GB specified for the virtual machine, and yet the failure remained. In my searches, I came across someone who’d been working on a similar setup<\/a> and found they’d used some additional tools I had not installed:<\/p>\n One of the messages that came up during the config stage had said it preferred bash to dash, but that it was going to access it via \/bin\/sh, so if I really wanted it to be happy, I should remap the symbolic link, which I did. Another message that comes up during the bitbaking suggests to do ‘. \/home\/user\/.oe\/environment-angstromv2012.05’ and then run bitbake something (I chose nano) without using .\/oebb.sh. So I gave that a try. It failed almost identically.<\/p>\n So, I got a borrowed Ubuntu 11.04 machine, as the memory note really seemed important. I started with cloning the setup-scripts repo, configuring for beaglebone, and running the update. Then I stopped, and did the Once nano built, I felt confident that I would finally be able to bitbake kernel\/virtual, so I started it and let it run, which it did within a few hours. I went ahead and bitbaked Now we should have what is needed to cross compile a kernel module for BeagleBone on Ubuntu. However, things aren’t just going to start being simple, are they? I set up my extremely basic kernel module:<\/p>\n And my Makefile:<\/p>\n And ran make, which resulted in this output:<\/p>\n This is disappointing. I figure that there may be some aspect to the way the bitbake setup is done that I’m causing problems with from my side, so I figure it’s time to pursue moving to the BeagleBone. (Note, there was a resolution to the above, found below related to using make ARCH=arm.)<\/p>\n I started with this in parallel to the effort on Ubuntu, by trying to get the kernel headers using So, I checked out http:\/\/feeds.angstrom-distribution.org\/feeds\/v2012.05\/ipk\/eglibc\/armv7a\/machine\/beaglebone\/, where sure enough the kernel-headers had been updated recently, so I ran Next, I decided to get a better idea of why I was getting conflicting information about what to use for KDIR in the Makefile. It seems that the standard is to have a symlink \/lib\/modules\/$(uname -r)\/build which points to a folder named for your linux kernel in \/usr\/src. What’s key is that there should be a Makefile here, which determines how kernel modules are built. So, I began a painfully slow scp of the output of the build on Ubuntu, first compressing setup-scripts\/build\/tmp-angstrom_v2012_05-eglibc\/work\/beaglebone-angstrom-linux-gnueabi\/linux-ti33x-psp-3.2.28-r16b+gitr720e07b4c1f687b61b147b31c698cb6816d72f01\/git to hopefully make the ordeal a bit faster.<\/p>\n With the copy ongoing, I decided to give another shot at the cross compiling. I was looking in my Embedded Linux Primer book and realized that I’d forgotten about passing ARCH=arm when calling make. So I went back to my cross compile environment, and navigated to the folder with the Makefile and the basic kernel module code, and ran Finally the tar.gz finished copying, so I extracted it to ~\/angstrom-build. As root, I symlinked this to a couple places:<\/p>\n Then I gave a quick try to building my kernel module, knowing it was likely I’d need to make modules and scripts, but wanting to see what might happen. The attempt yielded this error: This took a couple hours and make scripts didn’t seem to do anything. Once this was done, I was able to build the kernel module, however, trying to insert it gave the same issue as when I had tried to insert the cross compiled kernel module. So, I decided to check out what So I have two options; the long way being to try to setup the kernel I built on an SD card, or the shorter way, upgrading the kernel on my BeagleBone to see if maybe the kernel-dev package I installed previously can be used once the kernel is upgraded. I chose to try to upgrade the kernel using Note that I include directives to switch user (su) as you’ll need to be root in some cases. You may replace \/home\/user with ~, I typed it out because I noticed that the font made it look like a hyphen sometimes. The command mykernelmod.c<\/p>\n Makefile<\/p>\n Preface This post was written as I attempted to create a kernel module for BeagleBone. The contents includes my troubleshooting efforts and a final resolution as to the method I found which worked, found at the end of the post. … Continue reading
\nBeagleBone A6 (beaglebone:~$ uname -a
\nLinux beaglebone 3.2.28 #1 Sun Oct 21 15:51:05 CEST 2012 armv7l GNU\/Linux<\/code>)
\nUbuntu 11.04 via VMWare Player with the following installed:<\/p>\n\n
git clone git:\/\/github.com\/Angstrom-distribution\/setup-scripts.git\r\ncd setup-scripts\r\nMACHINE=beaglebone .\/oebb.sh config beaglebone\r\nMACHINE=beaglebone .\/oebb.sh update\r\nMACHINE=beaglebone .\/oebb.sh bitbake virtual\/kernel<\/pre>\n
NOTE: Error expanding variable buildhistory_get_imageinfo | ETA: 00:04:56\r\nNOTE: Error during finalise of \/home\/user\/setup-scripts\/sources\/meta-openembedded\/meta-initramfs\/recipes-bsp\/images\/initramfs-kexecboot-klibc-image.bb\r\nERROR: Failure expanding variable buildhistory_get_imageinfo, expression was \tif [ \"${@base_contains('BUILDHISTORY_FEATURES', 'image', '1', '0', d)}\" = \"0\" ] ; then\r\n\t\treturn\r\n\tfi\r\n\r\n...\r\nwhich triggered exception OSError: [Errno 12] Cannot allocate memory\r\nERROR: Command execution failed: Exited with 1\r\nNOTE: Error expanding variable buildhistory_get_imageinfo\r\nNOTE: Error during finalise of \/home\/user\/setup-scripts\/sources\/meta-openembedded\/meta-initramfs\/recipes-bsp\/images\/initramfs-kexecboot-image.bb<\/pre>\n\n
bitbake nano\r\nPseudo is not present but is required, building this first before the main build\r\nNOTE: angstrom DOES NOT support libiconv because the eglibc provided iconv library is used\r\nNOTE: angstrom DOES NOT support libiconv because the eglibc provided iconv library is used\r\nNOTE: Error expanding variable do_populate_sdk######### | ETA: 00:01:58\r\nNOTE: Error during finalise of \/home\/user\/setup-scripts\/sources\/openembedded-core\/meta\/recipes-core\/meta\/external-python-tarball.bb\r\nERROR: Failure expanding variable METADATA_REVISION, expression was ${@base_detect_revision(d)} which triggered exception OSError: [Errno 12] Cannot allocate memory\r\nERROR: Command execution failed: Exited with 1\r\nNOTE: Error expanding variable toolchain_create_sdk_version\r\nNOTE: Error during finalise of \/home\/user\/setup-scripts\/sources\/openembedded-core\/meta\/recipes-core\/meta\/meta-toolchain-gmae.bb\r\n\r\nSummary: There were 2 ERROR messages shown, returning a non-zero exit code.<\/pre>\n. \/home\/user\/.oe\/environment-angstromv2012.05<\/code> and then run bitbake nano<\/code> steps as previously suggested. This time was much more positive! Note that I disregarded the request to change \/bin\/sh to point to bash as the computer is a loaner. However, quite some time later, nano finished building. I hadn’t imagined it would take so long, so I wasn’t watching the clock, so I can only say it took several hours.<\/p>\nsystemd-image<\/code> as well, before finally bitbaking virtual\/kernel -c compile -f<\/code>, as suggested in the\u00a0similar setup<\/a> post I mentioned earlier. Finally this created files where the aforementioned post suggests, which look to be what is needed (for me the location was: \/home\/user\/setup-scripts\/build\/tmp-angstrom_v2012_05-eglibc\/work\/beaglebone-angstrom-linux-gnueabi\/linux-ti33x-psp-3.2.28-r16b+gitr720e07b4c1f687b61b147b31c698cb6816d72f01\/git).<\/p>\n#include <linux\/module.h>\r\n#include <linux\/kernel.h>\r\n\r\nstatic int __init enable_usermode(void)\r\n{\r\n printk(KERN_INFO \"Usermode enabled.\\n\");\r\n return 0;\r\n}\r\n\r\nstatic void __exit disable_usermode(void)\r\n{\r\n printk(KERN_INFO \"Usermode disabled.\\n\");\r\n}\r\n\r\nmodule_init(enable_usermode);\r\nmodule_exit(disable_usermode);<\/pre>\nobj-m += enable_usermode.o\r\n\r\nCROSS = \/home\/user\/setup-scripts\/build\/tmp-angstrom_v2012_05-eglibc\/sysroots\/x86_64-linux\/usr\/bin\/armv7a-angstrom-linux-gnueabi\/arm-angstrom-linux-gnueabi-\r\nKDIR = \/home\/user\/setup-scripts\/build\/tmp-angstrom_v2012_05-eglibc\/work\/beaglebone-angstrom-linux-gnueabi\/linux-ti33x-psp-3.2.28-r16b+gitr720e07b4c1f687b61b147b31c698cb6816d72f01\/git\r\n\r\nPWD := $(shell pwd)\r\n\r\nall:\r\n make -C $(KDIR) M=$(PWD) CROSS_COMPILE=$(CROSS) modules\r\nclean:\r\n make -C $(KDIR) M=$(PWD) CROSS_COMPILE=$(CROSS) clean<\/pre>\n
make -C \/home\/user\/setup-scripts\/build\/tmp-angstrom_v2012_05-eglibc\/work\/beaglebone-angstrom-linux-gnueabi\/linux-ti33x-psp-3.2.28-r16b+gitr720e07b4c1f687b61b147b31c698cb6816d72f01\/git M=\/home\/user\/LKM CROSS_COMPILE=\/home\/user\/setup-scripts\/build\/tmp-angstrom_v2012_05-eglibc\/sysroots\/x86_64-linux\/usr\/bin\/armv7a-angstrom-linux-gnueabi\/arm-angstrom-linux-gnueabi- modules\r\nmake[1]: Entering directory `\/home\/user\/setup-scripts\/build\/tmp-angstrom_v2012_05-eglibc\/work\/beaglebone-angstrom-linux-gnueabi\/linux-ti33x-psp-3.2.28-r16b+gitr720e07b4c1f687b61b147b31c698cb6816d72f01\/git'\r\n CC [M] \/home\/user\/LKM\/enable_usermode.o\r\ncc1: error: unrecognized command line option \"-m64\"\r\ncc1: error: unrecognized command line option \"-mno-red-zone\"\r\ncc1: error: unrecognized command line option \"-mcmodel=kernel\"\r\ncc1: error: unrecognized command line option \"-maccumulate-outgoing-args\"\r\nmake[2]: *** [\/home\/user\/LKM\/enable_usermode.o] Error 1\r\nmake[1]: *** [_module_\/home\/user\/LKM] Error 2\r\nmake[1]: Leaving directory `\/home\/user\/setup-scripts\/build\/tmp-angstrom_v2012_05-eglibc\/work\/beaglebone-angstrom-linux-gnueabi\/linux-ti33x-psp-3.2.28-r16b+gitr720e07b4c1f687b61b147b31c698cb6816d72f01\/git'\r\nmake: *** [all] Error 2<\/pre>\n
Compiling kernel modules directly on BeagleBone<\/h2>\n
opkg install kernel-headers<\/code>, however this gave errors:<\/p>\n$ opkg install kernel-headers\r\nInstalling kernel-headers (3.2.28-r16a+gitr720e07b4c1f687b61b147b31c698cb6816d72f01) to root...\r\nDownloading http:\/\/feeds.angstrom-distribution.org\/feeds\/v2012.05\/ipk\/eglibc\/armv7a\/machine\/beaglebone\/kernel-headers_3.2.28-r16a+gitr720e07b4c1f687b61b147b31c698cb6816d72f01_beaglebone.ipk.\r\nwget: server returned error: HTTP\/1.1 404 Not Found\r\nCollected errors:\r\n* opkg_download: Failed to download http:\/\/feeds.angstrom-distribution.org\/feeds\/v2012.05\/ipk\/eglibc\/armv7a\/machine\/beaglebone\/kernel-headers_3.2.28-r16a+gitr720e07b4c1f687b61b147b31c698cb6816d72f01_beaglebone.ipk, wget returned 1.\r\n* opkg_install_pkg: Failed to download kernel-headers. Perhaps you need to run 'opkg update'?\r\n* opkg_install_cmd: Cannot install package kernel-headers.<\/pre>\n
opkg update<\/code> as suggested. Unfortunately, using the same kernel module from earlier and the same Makefile with the KDIR changed to KDIR := \/lib\/modules\/$(shell uname -r)\/build<\/code> (and no CROSS_COMPILE), the result of running make<\/code> was a complaint:
\nmake: *** \/lib\/modules\/3.2.28\/build: No such file or directory.\u00a0 Stop.<\/code>
\nLooking into the directory, of course there is no build folder. The only thing I had installed was kernel-headers, which apparently is insufficient for the task of building kernel modules directly on BeagleBone. More disappointingly, I noticed that the only kernel-headers version now available is 3.2.30, while my BeagleBone has Angstrom 3.2.28.<\/p>\nmake ARCH=arm<\/code>. It built! In a flurry of excitement, I copied it to my BeagleBone and tried to insmod, only to be greeted with: insmod: error inserting 'enable_usermode.ko': -1 Invalid module format<\/code><\/p>\nln -s \/home\/beaglebone\/angstrom-build \/usr\/src\/linux-3.2.28\r\nln -s \/usr\/src\/linux-3.2.28 \/lib\/modules\/3.2.28\/build<\/pre>\n
\n\/bin\/sh: scripts\/basic\/fixdep: cannot execute binary file<\/code>
\nSo I went back to ~\/angstrom-build and ran<\/p>\nmake modules\r\nmake scripts<\/pre>\n
dmesg<\/code> had to say:
\nenable_usermode: disagrees about version of symbol module_layout
\nUh oh. It seems that even though the numerical version of the kernel matches, something else within the pre-built kernel distributed on the BeagleBone doesn’t match what I’ve built.<\/p>\nopkg upgrade<\/code>. With this selection, I went ahead and did make scripts<\/code> in \/usr\/src\/kernel before changing the Makefile to use KDIR = \/usr\/src\/kernel<\/code>, and voila! This time the kernel module built and was successfully inserted!<\/p>\nSuggested course of action to compile a kernel module on BeagleBone<\/h1>\n
exit<\/code> will take you back to the previous user, or if you are in the original user who signed in, will disconnect you (so don’t use exit if you only have one user, root). Finally, dmesg<\/code> will show the kernel prints, so you can look for the text from the example kernel module to be printed when you insert and remove the module.<\/p>\nopkg update\r\nopkg --tmp-dir \/home\/user upgrade\r\n*reboot if kernel upgraded using: shutdown -r now*\r\nopkg install kernel-headers\r\nopkg install kernel-dev\r\ncd \/usr\/src\/kernel\r\nsu\r\nmake scripts\r\nexit\r\ncd \/home\/user\r\nmkdir mykernelmod\r\ncd mykernelmod\r\n*create the below described c file*\r\n*create the below described Makefile*\r\nmake ARCH=arm\r\nsu\r\ninsmod mykernelmod.ko\r\ndmesg\r\nrmmod mykernelmod.ko\r\ndmesg\r\nexit<\/pre>\n
#include <linux\/module.h>\r\n#include <linux\/kernel.h>\r\n\r\nstatic int __init enable_mod(void)\r\n{\r\n printk(KERN_INFO \"My Kernel Module is enabled.\\n\");\r\n return 0;\r\n}\r\n\r\nstatic void __exit disable_mod(void)\r\n{\r\n printk(KERN_INFO \"My Kernel Module is disabled.\\n\");\r\n}\r\n\r\nmodule_init(enable_mod);\r\nmodule_exit(disable_mod);<\/pre>\nobj-m += mykernelmod.o\r\nKDIR = \/usr\/src\/kernel\r\nPWD := $(shell pwd)\r\n\r\nall:\r\n make -C $(KDIR) M=$(PWD) modules\r\nclean:\r\n make -C $(KDIR) M=$(PWD) clean<\/pre>\n
Some useful links<\/h2>\n
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