Software Academy

GDB CheatSheet

Running

#gdb     <program> [core dump]
                     Start GDB (with optional core dump).
# gdb    --args <program> <args…>
                    Start GDB and pass arguments
# gdb    --pid <pid>
                    Start GDB and attach to process.
set args <args...>
                     Set arguments to pass to program to be debugged.
run                Run the program to be debugged.
kill                Kill the running program.

Breakpoints

break <where>
                   Set a new breakpoint.
delete <breakpoint#>
                   Remove a breakpoint.
clear
                   Delete all breakpoints.
enable <breakpoint#>
                   Enable a disabled breakpoint.
disable <breakpoint#>
                   Disable a breakpoint.

Watchpoints

watch <where>
                    Set a new watchpoint.
delete/enable/disable <watchpoint#>
                    Like breakpoints.

<where>

function_name
                       Break/watch the named function.
line_number
                       Break/watch the line number in the current source file.
file:line_number
                       Break/watch the line number in the named source file.

Conditions

break/watch <where> if <condition>
                        Break/watch at the given location if the condition is met.
                        Conditions may be almost any C expression that evaluate to true or false.
condition <breakpoint#> <condition>
                        Set/change the condition of an existing break- or watchpoint.

Examining the stack

backtrace
where
                        Show call stack.
backtrace full
where full
                        Show call stack, also print the local variables in each frame.
frame <frame#>
                        Select the stack frame to operate on.

Stepping

step
                       Go to next instruction (source line), diving into function.
next
                       Go to next instruction (source line) but donʻt dive into functions.
finish
                       Continue until the current function returns.
continue
                        Continue normal execution.

Variables and memory

print/format <what>
                            Print content of variable/memory location/register.
display/format <what>
                            Like „print“, but print the information after each stepping instruction.
undisplay <display#>
                            Remove the „display“ with the given number.
enable display <display#>
disable display <display#>
                           En- or disable the „display“ with the given number.
x/nfu <address>
                           Print memory.
                           n: How many units to print (default 1).
                           f: Format character (like „print“).
                           u: Unit.
                          Unit is one of:
                                       b: Byte,
                                       h: Half-word (two bytes)
                                       w: Word (four bytes)
                                       g: Giant word (eight bytes)).

Format

a                     Pointer.
c                     Read as integer, print as character.


d                     Integer, signed decimal.
f                      Floating point number.
o                     Integer, print as octal.
s                     Try to treat as C string.
t                      Integer, print as binary (t = „two“).
u                     Integer, unsigned decimal.
x                     Integer, print as hexadecimal.

<what>

expression
                       Almost any C expression, including function calls (must be prefixed with a
                       cast to tell GDB the return value type).
file_name::variable_name
                       Content of the variable defined in the named file (static variables).
function::variable_name
                       Content of the variable defined in the named function (if on the stack).
{type}address
                       Content at address, interpreted as being of the C type type.
$register
                       Content of named register. Interesting registers are $esp (stack pointer), $ebp
                       (frame pointer) and $eip (instruction pointer).

Threads

thread <thread#>
                     Chose thread to operate on.

Manipulating the program

set var <variable_name>=<value>
                       Change the content of a variable to the given value.
return <expression>
                        Force the current function to return immediately,
                        passing the given value.

Sources

directory <directory>
                      Add directory to the list of directories
                       that is searched for sources.
list
list <filename>:<function>
list <filename>:<line_number>
list <first>,<last>
                       Shows the current or given source context.
                       The filename may be omitted. If
                        last is omitted the context starting at
                        start is printed instead of centered around it.
set listsize <count>
                        Show many lines to show in „list“.

Signals

handle <signal> <options>
                            Set how to handle signles. Options are:
                                 (no)print: (Donʻt) print a message when signals occurs.
                                 (no)stop: (Donʻt) stop the program when signals occurs.
                                 (no)pass: (Donʻt) pass the signal to the program.

Informations

disassemble
disassemble <where>
                                 Disassemble the current function or given location.
info args
                                 Print the arguments to the function of the current stack frame.
info breakpoints
                                 Print informations about the break- and watchpoints.
info display
                                 Print informations about the „displays“.
info locals
                                 Print the local variables in the currently selected stack frame.
info sharedlibrary
                                 List loaded shared libraries.
info signals
                                 List all signals and how they are currently handled.
info threads
                                List all threads.
show directories
                                Print all directories in which GDB searches for source files.
show listsize
                                Print how many are shown in the „list“ command.
whatis variable_name
                                Print type of named variable.