I am debugging linux ubuntu kernel using kgdb / remote gdb. I have 2 computers - ubuntu target and windows host. Computers are connected using serial port and null-modem cable.
KGDB support is enabled in target ubuntu system, command options fro KGDB:
kgdbwait kgdboc=ttyS0,115200
On my Windows system i have MinGW gdb build (x86_64):
GNU gdb (GDB) 7.4 Copyright (C) 2012 Free Software Foundation, Inc. This GDB was configured as "x86_64-w64-mingw32".
I start my target system and it waits till remote debugger connection. I enter the following commands in GDB window:
(gdb) set remotebaud 115200
(gdb) target remote COM4
My gdb is able to connect to target and prints the following:
Remote debugging using COM4
???() at kernel/debug/debug_core.c:1043 wmb(); /* Sync point after breakpoint */
I then enter command to set breakpoints to be able to return to gdb when OS is booted:
(gdb) b sys_sync
Breakpoint 1 at 0xffffffff8124a710
I also tried hardware-assisted breakpoints in another run of same setup:
(gdb) hbreak sys_sync
This breakpoint setup should lead to kernel beak back to debuger when i enter sync command from target ubuntu console.
After i hit continue in GDB, OS is booted OK, but i never able to bring control back to gdb. I tried setting breakpoints on sys_sync, i tried
echo g > /proc/sysrq-trigger
in all cases with no success.
Very interesting: if i dont initially set breakpoint in sys_sync, entering sync command later does nothing. If i set sys_sync breakpoint, entering sync command later do halt target computer completely - so i suppose breakpoint actually set in this case.
How to break into debugger? GDB becomes irresponsive to any CTrl-C commands, so no way to continue debuging after i initially hit continue.
May be architecture incompatibility (Windows gdb - Linux target) - but seems like breakpoints are really set.
Please help
