EBC Exercise 08a Cross-Compiling
I'm still working on this...
This class is about developing software for embedded Linux. So far we have been doing all of our development on the Beagle. This works well for small (and not so small) programs. However, we are now moving into kernel development and that's best done on a more powerful host computer. Here you learned how to download and install the cross-compilers and the source for kernel and u-boot. Now we'll use those tools.
First we'll check everything by compiling the Hello World program, then we'll try the kernel and u-boot.
Cross-compiling Hello World
Listing 2-4 on page 29 of the text is an embedded version of Hello World. If you've set up your git repository you will find it in helloWorld.c when you do a git pull. Compile and run it on your host to be sure it works.
host$ gcc helloWorld.c host$ ./a.out Hello, World! Main is executing at 0x400524 This address (0x7fff8260bdf8) is in our stack frame This address (0x601038) is in our bss section This address (0x601020) is in our data section
Now that you know it's working, let's cross compile it. First set the paths to find the cross-compilers. Put the following in a file, call it ~/.oe/crossCompileEnv.sh. Make sure the path is correct for your system. This is for a 32-bit linux.
# add cross tools to your path PATH=~/BeagleBoard/oe/build/tmp-angstrom_2010_x-eglibc/sysroots/i686-linux/usr/libexec/armv7a-angstrom-linux-gnueabi/gcc/arm-angstrom-linux-gnueabi/4.5.4:$PATH export ARCH=arm export CROSS_COMPILE=arm-angstrom-linux-gnueabi-
Here is for 64-bit
# add cross tools to your path PATH=~/BeagleBoard/oe/build/tmp-angstrom_2010_x-eglibc/sysroots/x86_64-linux/usr/libexec/armv7a-angstrom-linux-gnueabi/gcc/arm-angstrom-linux-gnueabi/4.5.4:$PATH export ARCH=arm export CROSS_COMPILE=arm-angstrom-linux-gnueabi-
Now source the file and compile again. (Note: you only have to source once per terminal session.)
host$ source ~/.oe/crossCompileEnv.sh host$ gcc helloWorld.c host$ file a.out a.out: ELF 32-bit LSB executable, ARM, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.16, not stripped
The file command tells what's in the file. In this case we have an ARM executable. Success! Now copy to your Beagle and run
host$ scp a.out root@beagle:. host$ ssh root@beagle ./a.out Hello, World! Main is executing at 0x8374 This address (0xbeb32d4c) is in our stack frame This address (0x10650) is in our bss section This address (0x10648) is in our data section
The scp copies a.out to the beagle and the ssh runs the a.out on the beagle. Notice the address are very different from the host version.
Finding the Kernel and Installing It
After doing this exercise you have a Beagle kernel on your host computer. Let's see if it works.
Once compiled the kernel is put in a file called uImage. You may have seen it in the FAT partition on your SD card. Let's find it on your host. One way to find it is
host$ cd ~/BeagleBoard/oe host$ find . -name "*uImage*" | grep 2.6.32 | grep boot
We are looking for uImage, but we only want the 2.6.32 version. The last grep file the file in the boot directory. Several lines are printed, but the one I'm interested in is:
The first part of the path (in italics) is the path to the kernel. Check it out.
host$ cd build/tmp-angstrom_2010_x-eglibc/work/beagleboard-angstrom-linux-gnueabi/linux-omap-psp-2.6.32-r110b+gitr5fc29e7b2a76a64a739f857858ef0b98294aa155/git host$ ls -F arch/ drivers/ Kbuild modules.order samples/ usr/ block/ firmware/ kernel/ Module.symvers scripts/ virt/ COPYING fs/ lib/ net/ security/ vmlinux* CREDITS include/ MAINTAINERS patches/ sound/ vmlinux.o crypto/ init/ Makefile README System.map Documentation/ ipc/ mm/ REPORTING-BUGS tools/
We'll be learning what's in many of these over the next couple of weeks. Remember this location. Let's find uImage.
host$ cd arch/arm/boot; ls -shF total 13M 4.0K bootp/ 6.3M Image* 4.0K Makefile 3.0M zImage* 4.0K compressed/ 4.0K install.sh 3.0M uImage host$ ls -l uImage -rw-r--r-- 1 beagle beagle 3144300 2011-12-08 01:02 uImage
It should have the date that you did the bitbake. Let's see if it runs on the Beagle
host$ scp uImage root@beagle:. host$ ssh root@beagle beagle$ cd /boot; ls -F total 18M 4.0K MLO@ 372K Module.symvers-2.6.32 1.4M System.map-2.6.32 80K config-2.6.32 4.0K u-boot.bin@ 0 uImage@ 3.1M uImage-2.6.32 8.9M vmlinux-2.6.32 beagle$ ls -l uImage lrwxrwxrwx 1 www-data www-data 13 May 12 2011 uImage -> uImage-2.6.32
So the uImage that is there is a symbolic link to uImage-2.6.32. Let's save the working uImage in a difference file and copy our new uImage in.
beagle$ mv uImage-2.6.32 uImage-2.6.32.orig beagle$ mv ~/uImage uImage-2.6.32
And then reboot.
beagle$ shutdown -r now
After a couple of minutes your should be back and running again. Check and see if you are really running the new kernel.
beagle$ uname -a Linux beagleboard 2.6.32 #3 PREEMPT Thu Dec 8 01:02:13 EST 2011 armv7l GNU/Linux
It worked! That's the date I compiled mine on.
Compile via make
When you use bitbake it sets up all the paths to use the correct cross compilers. You can also build the kernel or u-boot by using make if you set the paths yourself. Here's what you need to do. Put the following in a file, call it ~/BeagleBoard/oe/crossCompileEnv.sh. Make sure the path is correct for your system.
PATH=~/BeagleBoard/oe/build/tmp-angstrom_2008_1/sysroots/i686-linux/usr/armv7a/bin:$PATH # add cross tools to your path export ARCH=arm export CROSS_COMPILE=arm-angstrom-linux-gnueabi-
Note from Brian: On my machine I had to add ~/BeagleBoard/oe/build/tmp-angstrom_2008_1/sysroots/x86_64-linux/usr/armv7a/bin to $PATH
Then source the file and cd to the kernel directory and try a make.
$ source ~/BeagleBoard/oe/crossCompileEnv.sh $ cd ~/BeagleBoard/oe/build/tmp-angstrom_2008_1/work/beagleboard-angstrom-linux-gnueabi/linux-omap-psp-2.6.32-r88+gitra6bad4464f985fdd3bed72e1b82dcbfc004d7869/git $ make xconfig
To make the kernel and u-boot run
$ make uImage $ make u-boot
Where do these put the new uImage? It's not where bitbake puts them. Here's how I found them.
$ find . -name uImage
If you would prefer to maintain your own kernel source tree outside of OE, see these directions: BeagleBoardLinuxKernel Alternatively it is possible to run the official omap branch of the linux kernel. Take a peek at this page: BeagleBoard#Linux_kernel.