KGDB Quick Start

Contents

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1. Hardware setup
2. Software setup
3. Applying the kgdb patch
4. Compiling the kernel on the development machine
5. Starting the debug session
6. Useful links and miscellaneous information
   
   

Hardware setup

Use a Null modem serial cable to connect across the Target and Development machines .

[ Development machine ]----------------------------------[ Target machine ]

1-Hardware pinout for the null modem serial cable

OR

2-Hardware pinout for the null modem serial cable

Testing the working of the Null-modem serial cable.

On the Development machine :
stty ispeed 115200 ospeed 115200 -F /dev/ttyS0
cat testfile.txt > /dev/ttyS0

On the Target machine :
stty ispeed 115200 ospeed 115200 -F /dev/ttyS0
cat /dev/ttyS0

Target machine.

The following settings are used for the Remote debugging session, automatically.

<root #> stty -F /dev/ttyS0
speed 115200 baud; line = 0;
min = 1; time = 0;
-brkint -icrnl -imaxbel
-opost -onlcr
-isig -icanon -iexten -echo -echoe -echok -echoctl -echoke

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Software setup

1. Downloaded Linux kernel source : linux-2.6.6.tar.gz
2. Downloaded the 2.6.7 patch : patch-2.6.7.bz2
3. Downloaded the Kgdb patch : linux-2.6.7-kgdb-2.2.tar.bz2
   
   
4. Unzip the kernel sources & the kernel patch
   cd ${BASE_DIR}
   tar -zxvf linux-2.6.6.tar.gz
   bunzip2 patch-2.6.7.bz2
   ls ${BASE_DIR} --> linux-2.6.6 patch-2.6.7
   
   
5. mv ${BASE_DIR}/linux-2.6.6 ${BASE_DIR}/linux-2.6.7
   
6. cd ${BASE_DIR}/linux-2.6.7
   
7. patch -p1 < ${BASE_DIR}/patch-2.6.7

Applying the kgdb patch

1. Unzip the kgdb patch
   mkdir ${BASE_DIR}/patch-kgdb
   cd ${BASE_DIR}/patch-kgdb
   tar -jxvf linux-2.6.7-kgdb-2.2.tar.bz2
   
2. patch -p1 < ${BASE_DIR}/patch-kgdb/core-lite.patch
3. patch -p1 < ${BASE_DIR}/patch-kgdb/i386-lite.patch
4. patch -p1 < ${BASE_DIR}/patch-kgdb/8250.patch
5. patch -p1 < ${BASE_DIR}/patch-kgdb/eth.patch
6. patch -p1 < ${BASE_DIR}/patch-kgdb/i386.patch
7. patch -p1 < ${BASE_DIR}/patch-kgdb/core.patch

Compiling the kernel on the development machine

1. In the ${BASE_DIR}/linux-2.6.7/Makefile, set the EXTRAVERSION = -kgdb
   
2. make mrproper V=1
   
3. make xconfig V=1 or make oldconfig V=1
   Select the options appropriate for the target machine Hardware.
   Select the options pertaining to kgdb under "Kernel hacking" .
   Click to view the snapshot image
   
   
4. make clean V=1
5. make bzImage V=1
6. Transfer the built kernel to the Target machine from the Development machine .
   
   Copy the Kernel image from ${BASE_DIR}/linux-2.6.7/arch/i386/boot/bzImage to the target machine as /boot/vmlinuz-2.6.7-kgdb
   Copy the Map file from ${BASE_DIR}/linux-2.6.7/System.map to the target machine as /boot/System.map-2.6.7-kgdb
   Also create links,
   ln -s /boot/vmlinuz-2.6.7-kgdb /boot/vmlinuz
   ln -s /boot/System.map-2.6.7-kgdb /boot/System.map
   
   
7. Edit the /boot/grub/grub.conf file in the target machine to have the kgdb enabled kernel entry.
   Sample is shown below :-
   
   # Sample grub.conf which will by default boot the kgdb enabled kernel
   default=1
   timeout=10
   splashimage=(hd0,0)/boot/grub/splash.xpm.gz
   
   title RH
   root (hd0,0)
   kernel /boot/vmlinuz ro root=/dev/sda1
   initrd /boot/initrd
   
   title Linux-2.6.7-kgdb
   root (hd0,0)
   kernel /boot/vmlinuz-2.6.7-kgdb ro root=/dev/sda1 rootfstype=ext3 kgdbwait kgdb8250=0,115200
   

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Starting the debug session

1. After booting the target machine will wait for the host development machine to connect, by displaying the message :-
   
   Waiting for connection from remote gdb...
   
   
2. cd ${BASE_DIR}/linux-2.6.7
3. For setting a debug session with baud rate of 115200 on /dev/ttyS0 , run as "root" user:-
   
   <root#> gdb ./vmlinux
   GNU gdb Red Hat Linux (6.0post-0.20040223.17rh)
   Copyright 2004 Free Software Foundation, Inc.
   GDB is free software, covered by the GNU General Public License, and you are
   welcome to change it and/or distribute copies of it under certain conditions.
   Type "show copying" to see the conditions.
   There is absolutely no warranty for GDB. Type "show warranty" for details.
   This GDB was configured as "i386-redhat-linux-gnu"...Using host libthread_db library "/lib/tls/libthread_db.so.1".
   
   (gdb) shell echo -e "\003" > /dev/ttyS0
   (gdb) set remotebaud 115200
   (gdb) target remote /dev/ttyS0
   Remote debugging using /dev/ttyS0
   breakpoint () at kernel/kgdb.c:1212
   1212 atomic_set(&kgdb_setting_breakpoint, 0);
   warning: shared library handler failed to enable breakpoint
   (gdb)
   
   
4. For further commands refer http://kgdb.linsyssoft.com/tockdebug.htm
   

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Useful links and Miscellaneous information

1. Useful Links :
   http://kgdb.sourceforge.net/
   http://kgdb.linsyssoft.com/
   http://kgdb.linsyssoft.com/downloads/
   
   
2. Active Developer : Amit Kale --> [email protected]
3. Bug Report : [email protected]