Snippets for yer computer needs




full short desc
run ARG1 r run program
attach PID   attach gdb to already running process
next n step to next source line (ie don’t step in to subroutine)
step s step through program (steps into subroutines)
stepi si step one instruction exactly
continue c continue running program
break LOC b set breakpoint at function/line
tbreak LOC   set breakpoint that breaks only once
watch EXPR   stop execution when a variable changes
rwatch EXPR   stop execution when a variable is read
info breakpoints i b list of breakpoints
disable NUM dis disable a breakpoint
kill   stop execution of program

Stack info

full short desc
backtrace bt backtrace
backtrace full bt full backtrace (with locals for each frame)
list l list surrounding source
info locals i lo show local variables
info args i ar show arguments
info frame i f show info about stack frame
finish fin return from function
call   call function linked into program
up N   go up n frames in the stack
down N   go down n frames in the stack

Examine memory:

cmd desc
disassemble disassemble section of memory
p/x VAR print variable in hexadecimal
x ADDR Examine memory at addr
whatis VAR show variable type
set var VAR=VAL Set variable to value
info registers show registers (excluding floating point)
show env Show environment
set env FOO = bar Set environment variable FOO to bar
set env VAR=VAL Set environment variable to value
cmd desc
set print pretty on pretty print structures
set print array on readable array output
set print array-indexes on show array indices
set print demangle on demangle C++ names
macro expand MACRO expands a macro (requires -gdwarf-2 -g3 compiler flags)
source FILE source a GDB macro file
code print type
x hexadecimal
u unsigned int
d signed int
o octal
u unsigned decimal
t binary
f floating point
a address
c char
s string

Examine a core dump:

gdb executable coredump



LLDB <-> GDB Cheatsheet

command description
r ARGS run program (with arguments)
s step
env FOO=BAR set environment variable
frame variable list local variables
bt backtrace
disassemble -f disassemble frame

Bryan Cantrill

Debugging Under Fire (YouTube)

Debugging is the process by which we understand pathological behavior in a software system

The essence of debugging is asking and answering questions - and the craft of writing debuggable software is allowing the software to be able to answer questions about itself.

Recovery in lieu of understanding normalizes broken software.

Mike Perham

The Three Best Debugging Tools

  1. Your coworker
  2. Your ‘creative side’
  3. Your Mental Model of the System

I agree a lot with #3 - often when I’m helping someone debugging, it’s helping them establish this mental model.