Usage of kgdb in v2.6.26

Usage of kgdb in v2.6.26

[ZC Miao]

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 : 2.6.25.10-86.fc9.i686
5. Cpu : Intel(R) Core(TM)2 Duo CPU     T5450  @ 1.66GHz


* Firstly I compile kernel 2.6.26 with kgdb support :
CONFIG_KGDB=y
CONFIG_KGDB_SERIAL_CONSOLE=y

* 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=192.168.200.1:/path/to/rootfs,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
(gdb) 

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
(gdb) 
---------------------------------------------------------------

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
(gdb)  
---------------------------------------------------------------
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.

Thanks. 

--
ZC Miao (hellwolf.misty@gmail.com)
Blog http://hellwolf.cublog.cn

gpg --keyserver pgp.mit.edu --recv-key 0x6B174C6F

Most people deserve each other.
		-- Shirley

Re: Usage of kgdb in v2.6.26

[Jason Wessel]

Do you have CONFIG_DEBUG_RODATA=y in your kernel config?

There is a presently a known problem where breakpoints will silently
fail to plant when this is turned on.

Jason.

ZC Miao wrote:
> 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 : 2.6.25.10-86.fc9.i686
> 5. Cpu : Intel(R) Core(TM)2 Duo CPU     T5450  @ 1.66GHz
>
>
> * Firstly I compile kernel 2.6.26 with kgdb support :
> CONFIG_KGDB=y
> CONFIG_KGDB_SERIAL_CONSOLE=y
>
> * 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=192.168.200.1:/path/to/rootfs,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
> (gdb) 
>
> 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
> (gdb) 
> ---------------------------------------------------------------
>
> 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
> (gdb)  
> ---------------------------------------------------------------
> 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.
>
> Thanks. 
>
> --
> ZC Miao (hellwolf.misty@gmail.com)
> Blog http://hellwolf.cublog.cn
>
> gpg --keyserver pgp.mit.edu --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@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at  http://www.tux.org/lkml/
>   

Re: Usage of kgdb in v2.6.26

[ZC Miao]

$ cat ../../output/x86.kerneldev/.config| grep CONFIG_DEBUG_RODATA
CONFIG_DEBUG_RODATA=y

Yes, conigured.

On Thu, 2008-07-17 at 08:14 -0500, Jason Wessel wrote:
> 
> Do you have CONFIG_DEBUG_RODATA=y in your kernel config?
> 
> There is a presently a known problem where breakpoints will silently
> fail to plant when this is turned on.
> 
> Jason.
> 
> ZC Miao wrote:
> > 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 : 2.6.25.10-86.fc9.i686
> > 5. Cpu : Intel(R) Core(TM)2 Duo CPU     T5450  @ 1.66GHz
> >
> >
> > * Firstly I compile kernel 2.6.26 with kgdb support :
> > CONFIG_KGDB=y
> > CONFIG_KGDB_SERIAL_CONSOLE=y
> >
> > * 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=192.168.200.1:/path/to/rootfs,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
> > (gdb) 
> >
> > 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
> > (gdb) 
> > ---------------------------------------------------------------
> >
> > 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
> > (gdb)  
> > ---------------------------------------------------------------
> > 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.
> >
> > Thanks. 
> >
> > --
> > ZC Miao (hellwolf.misty@gmail.com)
> > Blog http://hellwolf.cublog.cn
> >
> > gpg --keyserver pgp.mit.edu --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@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > Please read the FAQ at  http://www.tux.org/lkml/
> >   
> 
--
ZC Miao (hellwolf.misty@gmail.com)
Blog http://hellwolf.cublog.cn

gpg --keyserver pgp.mit.edu --recv-key 0x6B174C6F

Regarding astral projection, Woody Allen once wrote, "This is not a bad way
to travel, although there is usually a half-hour wait for luggage."

Re: Usage of kgdb in v2.6.26

[ZC Miao]

Wow, that's a magic! It works now!

I think we should document it in the Documentation of kgdb.

Thanks!

On Thu, 2008-07-17 at 08:14 -0500, Jason Wessel wrote:
> 
> Do you have CONFIG_DEBUG_RODATA=y in your kernel config?
> 
> There is a presently a known problem where breakpoints will silently
> fail to plant when this is turned on.
> 
> Jason.
> 
> ZC Miao wrote:
> > 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 : 2.6.25.10-86.fc9.i686
> > 5. Cpu : Intel(R) Core(TM)2 Duo CPU     T5450  @ 1.66GHz
> >
> >
> > * Firstly I compile kernel 2.6.26 with kgdb support :
> > CONFIG_KGDB=y
> > CONFIG_KGDB_SERIAL_CONSOLE=y
> >
> > * 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=192.168.200.1:/path/to/rootfs,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
> > (gdb) 
> >
> > 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
> > (gdb) 
> > ---------------------------------------------------------------
> >
> > 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
> > (gdb)  
> > ---------------------------------------------------------------
> > 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.
> >
> > Thanks. 
> >
> > --
> > ZC Miao (hellwolf.misty@gmail.com)
> > Blog http://hellwolf.cublog.cn
> >
> > gpg --keyserver pgp.mit.edu --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@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > Please read the FAQ at  http://www.tux.org/lkml/
> >   
> 
--
ZC Miao (hellwolf.misty@gmail.com)
Blog http://hellwolf.cublog.cn

gpg --keyserver pgp.mit.edu --recv-key 0x6B174C6F

The human mind ordinarily operates at only ten percent of its capacity
-- the rest is overhead for the operating system.