LDD3 notes: Debugging

My notes while reading Linux Device Drivers 3rd edition.

printk_ratelimit() tells if we're not flooding the log

Kernel configuration

• CONFIG_DEBUG_SLAB -> canary killed
• CONFIG_DEBUG_SPINLOCK_SLEEP -> potential sleeps with spinlocks detected
• CONFIG_DEBUG_INFO, CONFIG_FRAME_POINTER for gdb debugging

seq_file - kernel in-memory file buffer, similar to open_memstream or ostringstream.

• a cleaner interface for implementing a /proc file
• iterator/visitor: start, show, next, stop
• api for the visitor: seq_printf into a seq_file
• fops implemented for reading

debugging a live kernel through a 'dynamic' core dump

• gdb vmlinux /proc/kcore, core-file /proc/kcore
• cannot modify data, breakpoint, watchpoint or single-step
• add-symbol-file for modules, using /sys/module/*/sections/.* like with a jtag emulator
• print *(address)

kdb -debugging from SGI

• ia32 only
• built-in to kernel, pause/break key as 'ctrl-c' takes you into debugger
• has breakpoints and can modify data
• sees module symbols automatically

kgdb -mm -variant

• serial port, ethernet kgdboe
• x86, ppc.
• no ARM

kgdb -sf.net variant

• serial port only
• x86, ppc.
• no ARM

Linux trace toolkit

DProbes

• vs kprobes?