Execution
| 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| 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 |
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.
The Three Best Debugging Tools
- Your coworker
- Your 'creative side'
- 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.