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Starting

gdb <executable>
gdb --args <executable> arg1 arg2 arg3

getting info

  • p[rint] var
  • ptype var
  • x /100bx m - eXamine memory located by variable m, print 100 bytes in hex format
  • bt (backtrace)
  • t (threads)

call stack

  • bt (backtrace)
  • frame 4 - switch to frame #4
  • up
  • down

breakpoints

  • break malloc
  • clear malloc
  • info break

stepping

  • s [tep]
  • c [ontinue] <num_to_ignore>
  • n [ext] - to next line
  • fin [ish] - execute until stack frame returns
  • u [ntil] <line number> - execute to line (to avoid loops)

symbols

  • set symbol-reloading on
  • add-symbol-file ~/mymodule.o 0xd8be4000

file paths and libraries

  • set verbose on
  • set auto-load safe-path /
  • info shared
  • set sysroot /home/niziak/n/3/out/host/usr/arm-buildroot-linux-uclibcgnueabi/sysroot

source paths

Search paths (prefixes):

  • dir /path/to/src1
  • dir /path/to/lib/src2

Translate beginning of paths:

  • set substitute-path /usr/lib ../../out/target/usr/lib

infos

  • show debug-file-directory

threads

  • info threads - show info about threads
  • thread 4 - switch to thread 4
  • print mutex

Kernel OOPS

Reading

PC is at RTMPCheckEtherType+0x90/0x4d4 [mt7601Uapsta]
LR is at RTMPCheckEtherType+0x34/0x4d4 [mt7601Uapsta]

Code: e59f3418 e0256593 e2859d43 e289902c (e5d939ba)

Oops occurs at offset 0x90 from RTMPCheckEtherType. 0x4d4 is length. “Code” line shows last instruction. Instruction in bracket is problematic instruction (at RTMPCheckEtherType+0x90)

Tracing

Disassembly kernel binary or module binary: objdump -dS vmlinux > /tmp/kernel.s and look into generated code.

Python

apt-get install gdb python2.7-dbg
gdb python <pid>

DRAFTS

call raise(kernel-thread-id, signo) or call pthread_kill(pthread-thread-id, signo).