kernel debugging

NoiseEHC NoiseEHC at
Mon Aug 3 15:50:14 EDT 2009

Somehow every time I asked about debugging in these forums I have got no 
answer at all. Now I have a weak feeling that Linux developers are "real 
programmers" who do not use debuggers. I hope it is not the case... :)
> 2.
> I looked into using the USB port with gadget support. I am attaching 
> the kernel config if you are interested in. I have compiled 
> amd5536udc.ko, g_serial.ko and g_android.ko as modules (so I can look 
> at error messages while doing an insmod). (Kernel 2.6.29, g_android.ko 
> would enable debugging via USB with the adb - Android debugging bridge.)
> If I do not insmod amd5536udc.ko, then both g_android.ko and 
> g_serial.ko bark me about missing usb_gadget_register_driver symbol.
> If I do insmod amd5536udc.ko then both modules bark about "(No such 
> device)" error.
> What is not clear whether this amd5536udc.ko is usable at all because 
> I am booting the XO-1 from an USB stick so can the AMD southbridge be 
> used for both host and device at the same time?
> What device does it need?
I succeeded compiling kdb into the kernel, and I have an USB keyboard 
(and successfully realized what must be compiled into the kernel) so I 
can press the Pause button to break into the debugger. However when I 
exit kdb crashes the machine so this way I cannot debug the g_android.ko 
I would appreciate some answer to any one of these questions:
1. What is the Pause button on the XO keyboard? (And which is the SysRq?)
2. If there are no such buttons then how can I change the required 
button? Is it wired into the kernel or to kdb's keyboard handler?
> 3.
> It happened that one of the hardware in my room had a FTDI usb to 
> serial converted. I pluggeg it into the XO-1 and insmod usbserial.ko 
> then insmod ftdi_sio.ko and both worked. However I do not have a 
> "/dev/ttyUSB..." entry. It can be that because the system does not run 
> udev or similar it does not automatically create /dev entries? If so 
> then how can I do this? (I see that the init srcript uses "mdev -s") 
> Another issue is that this serial stuff will be loaded much later than 
> kernel start so if I define "console=/dev/ttyUSB0" in the kernel 
> parameters and the device will be created later then will Linux pick 
> up the device at that time?
It seems that if I use mdev -s then /dev/ttyUSB0 appears. What I found 
is that in the hardware I pulled the FTDI converter had a cable similar 
what I just needed so I plugged the cable into my PC's motherboard, its 
plug into the serial cable, the serial cable's plug into the FTDI bridge 
and the bridge into the XO-1. Then I started getty ttyS0 or something 
similar and nothing happened. Exactly how could I test the setup?

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