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Connection problems
gdb prints following errors on giving command target remote.
Ingore packet error, continuing...
Ingore packet error, continuing...
Ingore packet error, continuing...
Couldn't establish connection to remote target
Malform response to offset query, timeout.
Check whether the serial line speed given to the test kernel from
lilo.conf file on the test machine is same as the serial line speed on
the developement machine. They should be equal.
Check whether the serial line is working properly. Boot the test
machine in a non-debug kernel and check whether characters sent into
the serial line from either end of the serial line appear on the other
end. This can be done as follows:
- Boot the test machine with the kernel that came with redhat
installation. On the developement machine run cat < /dev/ttyS0.
It will wait for some characters to come from the serial line.
- On the test machine run echo hello> /dev/ttyS0
- The cat running developement machine machine should show "hello".
There could be some extra end of lines. Ignore them.
- Now kill the cat and repeat the same procedure with cat on the
test machine and echo on developement machine. This time the cat on
test machine should show "hello".
If either of the machines don't show hello you know that characters are
not being sent. Check the serial line to see whether you have wired it
incorrectly if that is the case.
Check whether the prompt send by kgdb is received on the
developement machine. This can be done as follows:
- Run minicom on the serial line on the developement machine. Setup
serial line baud rate to appropriate value.
- Now boot the test kernel.
- When the message Waiting for connection from remote gdb...
appears on the console of the test machine, following characters should
be seen in minicom. +$S05#b8. This character string may
repeat. It is the prompt sent to gdb from kgdb. If you don't see this
serial line speed is set incorrectly on one of the machines.
Problems with breakpoints
A breakpoint does not get hit as expected: Check whether you are using
appropriate vmlinux file. Print the address of the
function sys_close from gdb:
(gdb) p sys_close
$1 = {long int (unsigned int)} 0xc013212c <sys_close>
Print address of the same function using proc filesystem on the
test machine.
$ grep sys_close /proc/ksyms
c013212c sys_close_Rsmp_268cc6a2
The the address is not same, c013212c in above case, vmlinux file being
used is incorrect.
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