KGDB, Remote connection Error

Question

Im very New to KGDB, Im getting problem when im connecting the target from Host, Getting The following Error.

(gdb) target remote /dev/ttyUSB0
Remote debugging using /dev/ttyUSB0
Ignoring packet error, continuing...
warning: unrecognized item "swreak" in "qSupported" response
warning: unrecognized item "ReloInsn" in "qSupported" response
warning: unrecognized item "QTread'
[3]kdb> " in "qSupported" response
Bogus trace status reply from target: qTStatus
...

#

The Procedure Im following is :

[Target] stty -F /dev/ttyS0 115200
[Host] stty -F /dev/ttyUSB0 115200

Make sure the serial connection works on both direction. You can use:

[Host] cat /dev/ttyUSB0
[Target] echo 'from TARGET to HOST' > /dev/ttyS0

[Target] cat /dev/ttyS0
[Host] echo 'from HOST to TARGET' > /dev/ttyUSB0

You should see the messages on both side of machine. If not, there might be some problems on the cable or driver.

Compile Kernel

Enable KGDB* , KGDB_SERIAL*, KGDB_USB*, DEBUG_INFO, DEBUG_INFO_DWARF4, MAGIC_SYSRQ in the kernel config. Compile and install on the TARGET.

The main purpose here is to enable KGDB feature & preserve debug information in vmlinux.

agent-proxy Setup

agent-proxy acts as a proxy for the TARGET's serial port. It splits up the serial port for multiplexing. One for primary console I/O, the other for GDB session. Thus, we can work on both simultaneously. You should run the agent-proxy on HOST machine.

git clone http://git.kernel.org/pub/scm/utils/kernel/kgdb/agent-proxy.git
cd agent-proxy ; make
./agent-proxy 5550^5551 0 /dev/ttyUSB0,115200

This will redirect:

• TARGET's console to HOST:5550
• TARGET's kgdb listening port to HOST:5551

Start To Debug

First, open the primary console:

[Host] telnet localhost 5550

Entering the kdb mode, either by:

[Target] echo ttyS0,115200 > /sys/module/kgdboc/parameters/kgdboc
[Target] dmesg | tail

(you should see KGDB: Registered I/O driver kgdboc, otherwise it failed)

[Target] echo g >/proc/sysrq-trigger
Host> gdb vmlinux
(gdb) target remote localhost:5551
Remote debugging using localhost:5551
kgdb_breakpoint () at kernel/debug/debug_core.c:1072
1072             wmb(); /* Sync point after breakpoint */
(gdb)

#

when i type kgdb in target mission it is getting error as Permission denied as shown below

[3]kdb> kgdb
diag: -22: Permission denied

..., I would appreciate the clear answer in steps..., Thanks in advance

Answer 1

diag: -22: Permission denied

That error means that access to debugger functions is prohibited by default in you kernel. In order to unlock debugger you need exec this command:

echo 1 > /sys/module/kdb/parameters/cmd_enable

or add a Kernel Boot Parameter:

kdb.cmd_enable=1

More info here