Usage of kgdb in v2.6.26

From: ZC Miao
Date: Wed Jul 16 2008 - 18:00:30 EST

I tried to use the kgdb from v2.6.26, but met few problems.
I use :
1. gdb 6.8 (gdb-6.8-11.fc9.i386)
2. kernel v2.6.26 source code
3. Qemu 0.9.1 (qemu-0.9.1-5.fc9.i386)
4. Host is :
5. Cpu : Intel(R) Core(TM)2 Duo CPU T5450 @ 1.66GHz

* Firstly I compile kernel 2.6.26 with kgdb support :

* Then I use qemu to boot my kernel along with a rootfs that I created,
with a qemu option that makes a local tcp port a listening service as a
serial port for the emulated system. The kernel arguments I gave is :
nfsroot=,udp,nolock ip=dhcp root=/dev/nfs
ro single kgdboc=ttyS0,115200 kgdbwait

* After the kernel loaded and boot for a while, the gdb receives a
signal and hangs the kernel :
kgdb_register_io_module (new_kgdb_io_ops=<value optimized out>)
at /data/home/hellwolf/mydoc/prog/linux/linux-2.6/kernel/kgdb.c:1674

Question 1 :
* If I type "b sys_read", and then "c", the kernel continues until I
get :

[New Thread 1]
Cannot remove breakpoints because program is no longer writable.
It might be running in another process.
Further execution is probably impossible.

Breakpoint 1, sys_read (fd=3, buf=0xbfdb31dc "", count=512)

at /data/home/hellwolf/mydoc/prog/linux/linux-2.6/fs/read_write.c:360

Why "program is no longer writable" happens here?

Question 2 :
* If I directly type "c" when kgdbwait triggered. And use Sys-Rq+G to
interrupt the kernel, I will get :
[New Thread -1]

Program received signal SIGTRAP, Trace/breakpoint trap.
[Switching to Thread -1]
sysrq_handle_gdb (key=103, tty=0xc78f6400)
at /data/home/hellwolf/mydoc/prog/linux/linux-2.6/kernel/kgdb.c:167
Here if I type "c sys_read" and "c", it never actually makes any break
points, I will never receive a break from gdb.

I don't know if I made anything wrong, or I missed any important thing,
so I post here and would like to get some help from you.


ZC Miao (hellwolf.misty@xxxxxxxxx)

gpg --keyserver --recv-key 0x6B174C6F

Most people deserve each other.
-- Shirley

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at