Debugging C/C++ with LLDB

2021-05-30

The line pointed to by the arrow is the next line to be executed.

Short Commands

r: run
c: continue
b: break
n: next
Enter: repeat last command
s (step): step into a function
q: quit

How to Use LLDB

  1. Generate source-level debug information:

    gcc -g hello.c

  2. Run LLDB on the executable:

    lldb a.out

  3. Run the program:

    (lldb) run

Setting Breakpoints

(lldb) breakpoint set -f demo.cpp -l 10
(lldb) br s -f demo.cpp -l 10
(lldb) b demo.cpp:10

Breakpoints with Symbols

On a function:

(lldb) b square

On a class method:

(lldb) b Demo::demo

Inside a namespace:

(lldb) b LLDBDemo::add

Manipulating Breakpoints

Listing breakpoints:

(lldb) br list

Deleting breakpoints:

(lldb) br del 1
(lldb) br del

Stepping Around

Step over:

(lldb) next
(lldb) n

Step into:

(lldb) step
(lldb) s

Step out:

(lldb) finish

Continue:

(lldb) continue
(lldb) c

Inspecting Variables

Print variable contents:

(lldb) p varname
(lldb) print varname

Frame variables (see all visible variables):

(lldb) frame variable
(lldb) fr v

Current line:

(lldb) frame select

Backtrace and Frames

Backtrace:

(lldb) bt

Switching frames:

(lldb) frame select 0
(lldb) f 2

Using Watchpoints

Program must be running to set watchpoints.

Global variable:

(lldb) watchpoint set variable globalVariable
(lldb) watchpoint set variable -w read | write | read_write globalVariable

Member variable:

(lldb) b main
(lldb) run
(lldb) w s v d.memberVar

Terminating

Kill process:

(lldb) kill

Exiting:

(lldb) quit
(lldb) q

Additional Tips

  • Repeat last command: Press Enter
  • Set breakpoint at function: b main or b func_name
  • Print variable: print varname or p varname
  • Print all variables: fr v
  • Show help: help or help <command>

References