N8x0 support in linux-omap

Current kernel: 2.6.31-rc1-omap1

Startup plan

find optimal debugging techniques and real HW/qemu split;

make minimal working/debuggable configuration;

compile domain glossary.

Debug interfaces

Subsystems' status

Debugging in qemu

Need CONFIG_DEBUG_INFO=y in kernel configuration for symbolic debugging to work.

Kernel command line parameters

initcall_debug=1 – make kernel print all _init function calls during kernel_init;

Magic numbers

0x80000000 – here the kernel is loaded

0x80008000 – here we jump after decompression (.text.head that has VA of 0xc0008000 has PA 0x80008000 until MMU is active)

0xc0026000 – 'arm-linux-gnu-objdump -x vmlinux' says that .text starts here

Script for gdb session

target remote 127.0.0.1:1234
break *0x80008000

To debug compression-related stuff from the very beginning (start, arch/arm/boot/compressed/head.S) till start_kernel:

add-symbol-file ~/ws/osll/omap/20090610/linux-omap-2.6/arch/arm/boot/compressed/vmlinux 0x80000000

To debug kernel from stext (arch/arm/kernel/head.S) until MMU is active:

add-symbol-file ~/ws/osll/omap/20090610/linux-omap-2.6/vmlinux 0x80026000 -s .text.head 0x80008000

To debug kernel from start_kernel (init/main.c):

add-symbol-file ~/ws/osll/omap/20090610/linux-omap-2.6/vmlinux 0xc0026000

"Blank screen" debugging

Whatever happens, ^C breaks into the running kernel. If the screen is blank, dmesg-like log may be viewed through

x/10000s log_buf

Or even through

dump memory kmsg.log log_buf log_buf+10000

Debugging on real HW

Dealing with retu watchdog

Need to periodically touch it, like this:

while true
do
echo 63 > /sys/devices/platform/retu-watchdog/period
sleep 1
done