Debuggin Linux Kernel using JTAG (In ARM)

19 July, 2014 | ruchin

Build a kernel with symbols.

make menuconfig
 -> kernel hacking 
       -> Select Compile the kernel with debug info.

This will create a elf image (vmlinux) with can be understood by the trace32. The best choice is to use a uncompressed kernel. ake the following changes to cmm files.

Remove the aborts. Aborts are normal after mmu is initalized, so if you let the Debugger break for aborts, you will be aborting for ever. So remove the aborts


For adding the Linux menu in Trace32, the following lines will help. The cmm files for these are already available in the latest version of the Trace32.

MENU.ReProgram linux

Load the kernel into your regular load location

Using the following command

data.load.elf c:\vmlinux /strippart 4 /gnu /sourcepath y:\kernel

For source code debugging you need to give the /strippart. If you are directly running Trace32 in linux and giving the path to your actual kernel image, then it is not needed. But, most often our Trace32 environment is in windows. So we need to give how many paths to the stripped from the elf path.

For e.g., If you have compiled the kernel from /home/user1/proj1/kernel/ In windows if your source is here Y:\kernel Then you should strip /home/user1/proj1/kernel/ which is 4.

When do you need to jump to vmlinux?

This is exactly after your u-boot jumps to kernel image after decompressing. This could be tricky. Just check the u-boot logs and find where the kerenl is decompressed. It could be some address like 0x00008000. First, put a “HW breakpoint”there. Once, you hit the breakpoint it means the U-Boot is ready to jump to the kernel. At this moment change the kernel in the ram by using d.load.elf command shown above. You should see the initial instructions in 0x000080000. These are the same instructions seen in arch/arm/kernel/head.S. You can put some breakpoints now and stop the execution flow.

For debugging interrupts the ISR’s are located in virtual address from 0xFFFF0000.

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