**Linux Debugging**

^ Reference | {{:mywiki:linux:linux_debugging_techniques.ppt|}} |

====== Linux Debugging with LauterBach ======

===== Basic requirement =====

In order to support c source code level debugging, it is a must to enable debugging option during compile


==== Get source code directory base ====

<file C>
    mips-openwrt-linux-objdump -g vmlinux | grep -i DW_AT_comp_dir | grep -i indirect |  grep '\/'
</file>

Its output is like:
<file>
    <bb2043>   DW_AT_comp_dir : (indirect string, offset: 0x171): /disk/fs1/tmp2/openwrt/core/kernel_tree
</file>
==== Discover entry point in ELF ====
    * Discover vmlinux entry point
<file>
     mips-openwrt-linux-objdump -t vmlinux | grep -w "_text"
</file>

Its output in my setup: **60020000 g       .text  00000000 _text **
    * Discover kernel_entry
<file>
    mips-openwrt-linux-objdump -f vmlinux
</file>    

Its output in my setup: **start address 0x6002df00**

==== Generate system.map ====
<file>
    mips-openwrt-linux-nm -n vmlinux | grep -v '\( [aNUw] \)\|\(__crc_\)\|\( \$[adt]\)' > System.map
</file>

=== Get one symbol's address ===
<file>
    mips-openwrt-linux-objdump -t vmlinux | grep dp_xmit
</file>

===== Lauterbach/Debugger ===== 

==== Load symbol from linux PC via networking ====
Suppose below working environment:
| Linux Compilation folder via [[linux_debugging_with_lauterbach#get_source_code_directory_base|method]] | /disk/fs1/tmp2/shaoguoh/project/ugw61_grx500/openwrt/core/kernel_tree |
| vmlinux folder | /disk/fs1/tmp2/shaoguoh/project/ugw61_grx500/openwrt/core/kernel_tree |
| samba mapping folder to windows | X:\tmp2\shaoguoh\project\ugw61_grx500\openwrt\core\kernel_tree |

Lauterbach command: 
<file>
  d.load.elf "X:\tmp2\shaoguoh\project\ugw61_grx500\openwrt\core\kernel_tree\vmlinux" /strippart "/disk/fs1/tmp2" /path "X:\tmp2" /nocode
</file>

Note: 
  * /strippart : remove the directory prefix in the elf's debugging source file's 
  * /path: change to samba folder
  * /nocode: don't load code, but symbol only

**Example**: 

If the location of one file in vmlinux debugging as below: 
    /disk/fs1/tmp2/shaoguoh/project/ugw61_grx500/openwrt/core/kernel_tree/t.c
After /strippart "/disk/fs1/tmp2", ie, strip the prefix as specified here, it become:
    shaoguoh/project/ugw61_grx500/openwrt/core/kernel_tree/t.c
After  /path "X:\tmp2", ie, add prefix as specified here, it become:
    X:\tmp2\shaoguoh/project/ugw61_grx500/openwrt/core/kernel_tree/t.c    

With this folder, now debugger can access this file via samba from windows

====== Linux Kernel Debugging Tools ======
===== Enable kernel debug to detection lock/context issue =====
In openwrt/core, run: make kernel_menuconfig
In kernel_hack, enable below items:
{{:mywiki:linux:kernel_hack.jpg|}}