Several gdb macros useful for kernel debugging are defined in gdb scripts available from the downloads page. The scripts containing these macros are sourced in gdb to load their definitions into gdb. The recommended way of loading these macros is to source these gdb scripts from a .gdbinit file kept in the kernel source top level directory. gdb reads .gdbinit file in the directory where it is executed and runs commands given in the file.

Hardware debugging

kgdb versions 1.7 onwards support hardware breakpoint commands from gdb, so following commands don't apply to them. Use gdb hardware watchpoint commands instead.

kgdb supports debugging capabilities available in IA32 hardware. Three types of IA32 hardware breakpoints are supported by kgdb: data write watchpoint, instruction execution breakpoint and data access watchpoint.  The difference between hardware breakpoints and software breakpoints in gdb is that gdb modifies code for  inserting a breakpoint, whereas hardware breakpoints without modifying the code. Only 4 hardware breakpoints and watchpoints are available. Each hardware breakpoint can be of one of the three types: execution, write, access.

• An Execution breakpoint is triggered when code at the breakpoint address is executed.
• A write breakpoint ( aka watchpoints ) is triggered when memory location at the breakpoint address is written.
• An access breakpoint is triggered when memory location at the breakpoint address is either read or written.

A write or access hardware breakpoint can be defined over an address range of 1 to 4 bytes. The address range length is called length of the breakpoint. Length of an access or a write breakpoint defines length of the datatype to be watched. The length is 1 for char ( 1 byte ), 2 for short  ( 2 bytes ) and 3 for int (4 bytes ).

Commands hwebrk, hwwbrk and hwabrk place an execution, a write and an access breakpoint respectively. Use hwrmbrk command to remove a hardware breakpoint. These commands take following arguments.

1. breakpointno: 0 to 3
2. length: 1 to 3
3. address: Memory location in hex ( without 0x ) e.g c015e9bc

hwebrk breakpointno address
hwwbrk breakpointno length address
hwabrk breakpointno length address
hwrmbrk breakpointno

The command exinfo can be used to find which hardware breakpoint occurred.

A script  hwdebugmacros contains definitions of these macros.

( Examples of using hardware breakpoints to be added )

Process information

psmacros file contains definitions of process information macros.
The ps macro lists process ids and their names. It is useful for thread analysis.
The psname macro prints name of the process with given id.

( Examples of using the macros to be added )

Miscellaneous

Several gdb macros useful for kernel debugging are defined in gdb scripts available from the downloads page. The scripts containing these macros are sourced in gdb to load their definitions into gdb. The recommended way of loading these macros is to source these gdb scripts from a .gdbinit file kept in the kernel source top level directory. gdb reads .gdbinit file in the directory where it is executed and runs commands given in the file.