Linux Kernel Architecture

Mauerer runapp02.tex V2 - 09/04/2008 6:09pm Page 1172

Appendix B: Working with the Source Code

Figure B-8: Examining data structures of the local kernel.

If no type information is present for a pointer (this is, frequently the case in doubly linked standard lists),

C-style typecasts can be specified in theGDBinput field.

TheData->Detect Aliasesoption must be enabled to instructDDDto detect pointers to the same memory

area and to redirect the arrows to an existing representation of the structure rather than inserting a new

graphic representation. This is the case in the previous example, as indicated by theparentpointers

that all (correctly) point to the same element. Note however thatDDDis much slower than usual when it

operates in this mode.

Thecorefiles are not normally modified when they are processed by a debugger, soGDBdoes not notice

if any change is made to a value in kernel memory — changes are propagated via thekcorefile. If the

memory contents that are relevant to a user change, the user must explicitly reload the core file withcore

/proc/kcore.DDDautomatically displays values that have changed against a yellow background so that

they are easy to recognize.

B.5.3 KGDB

Two machines connected via a network or a serial cable provide a better debugging setup with practically

all the same options as are available when debugging normal applications. TheKGDBpatch installs a