Coredump analysis (GDB)

Setup

$ cat /proc/sys/kernel/core_pattern ... get coredumps location
$ ulimit -c                         ... check max coredump size
$ gdb <executable> <coredump>       ... load coredump with GDB

Threads & Stack

info threads        ... show running threads
thread apply all bt ... show the bt of all running threads
thread <idx> bt     ... show the bt of specific thread
thread <idx>        ... switch to other thread

bt [<lvl's>]        ... show the bt of the current thread
up                  ... move up in bt
down                ... move down in bt
f <idx>             ... select frame <idx>
info f              ... shows selected frame

Functions & Variables

list [function]            ... show source code
disas [/<m>] [function]    ... show disassembly

<m> (mode)
  - b ... prints bytes and instruction (in memory order)
  - m ... prints assembly and sources (not useful with optimized code)
  - r ... prints bytes and instruction (in instruction order)
  - s ... prints assembly and sources

info register              ... show registers
info args                  ... show parameters
info locals                ... show local variables

ptype [variable]           ... show type of variable
p[/<f>] $<register>        ... print register
p[/<f>] <variable>         ... print variable
p[/<f>] &<variable>        ... print address of variable
p[/<f>] *<variable>        ... print dereferenced variable
p[/<f>] *this              ... print member variables
p[/<f>] sizeof(<var|type>) ... print size of variable/type

<f> (format)
  - t ... binary
  - x ... hexadecimal
  - d ... signed decimal
  - u ... unsigned decimal
  - o ... octal
  - a ... address
  - c ... character
  - f ... float point
  - s ... string

p $_siginfo ... show signal details

p <vec>._M_impl._M_start+<idx> ... get item of vector

Memory

info proc mappings ... show memory mapping

x/<n><f><u> <addr> ... print memory

<n> (number)

<f> (format)
  - Basic types see <f> for print
  - i ... instruction

<u> (unit)
  - b ... byte (8-bit integer)
  - h ... half word (16-bit integer)
  - w ... word (32-bit integer)
  - g ... giant word (64-bit integer)

Additional

– Basic assembler instructions (x64, A64)
– Adding dependencies to coredump (GDB)
– Unwind the stack even if GDB can’t? (ARM)
– Print stack frames from stack (GDB)