Question

Does anyone know of a really good tutorial, book or article on debugging using GDB for MacOS and iOS? Particularly something that covers the commands added by Apple such as “po” (print object) as well as standard GDB commands. Thanks!

Answer 1

Have you tried gdb itself? You can type ‘help’ at a ‘(gdb)’ prompt to get a list of command categories, ‘help ‘ to get a list of commands in a given category, and ‘help ‘ to get help with a specific command. For example:

(gdb) help data
Examining data.

List of commands:

append -- Append target code/data to a local file
call -- Call a function in the program
delete display -- Cancel some expressions to be displayed when program stops
delete mem -- Delete memory region
disable display -- Disable some expressions to be displayed when program stops
disable mem -- Disable memory region
disassemble -- Disassemble a specified section of memory
display -- Print value of expression EXP each time the program stops
dump -- Dump target code/data to a local file
enable display -- Enable some expressions to be displayed when program stops
enable mem -- Enable memory region
inspect -- Same as "print" command
invoke-block -- Invoke the function associated with the block passed in as the first
mem -- Define attributes for memory region
output -- Like "print" but don't put in value history and don't print newline
print -- Print value of expression EXP
print-object -- Ask an Objective-C object to print itself
printf -- Printf "printf format string"
ptype -- Print definition of type TYPE
restore -- Restore the contents of FILE to target memory
set -- Evaluate expression EXP and assign result to variable VAR
set variable -- Evaluate expression EXP and assign result to variable VAR
undisplay -- Cancel some expressions to be displayed when program stops
whatis -- Print data type of expression EXP
x -- Examine memory: x/FMT ADDRESS

Type "help" followed by command name for full documentation.
Command name abbreviations are allowed if unambiguous.

That’s not going to help you much if you’ve never debugged a program, but if you know what to do with a debugger it’s probably all you need.