lldb

Original：🇺🇸 English
Translated

LLDB debugger skill for C/C++/Swift/Objective-C programs. Use when debugging with LLDB on macOS, FreeBSD, or Linux-clang environments, mapping GDB mental models to LLDB commands, using LLDB in Xcode or VS Code, or debugging Swift/Objective-C. Activates on queries about LLDB commands, GDB to LLDB migration, Apple platform debugging, LLDB Python scripting, or IDE-integrated debugging with clang-built binaries.

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Sourcemohitmishra786/low-level-dev-skills
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NPX Install

npx skill4agent add mohitmishra786/low-level-dev-skills lldb

Tags

Translated version includes tags in frontmatter
lldb-debuggergdb-lldb-migrationapple-platform-debugginglldb-python-scriptingide-debug-integration

SKILL.md Content

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LLDB

Purpose

Guide agents through LLDB sessions and map existing GDB knowledge to LLDB. Covers command differences, Apple specifics, Python scripting, and IDE integration.

Triggers

  • "I'm on macOS and need to debug a C++ program"
  • "How does LLDB differ from GDB?"
  • "How do I do [GDB command] in LLDB?"
  • "LLDB shows 
    <unavailable>
    for variables"
  • "How do I use LLDB in VS Code?"
  • "How do I write an LLDB Python script?"

Workflow

1. Start LLDB

bash
lldb ./prog                         # load binary
lldb ./prog -- arg1 arg2            # with arguments
lldb -p 12345                       # attach to PID
lldb -c core.1234                   # load core dump
lldb ./prog core.1234               # binary + core

2. GDB → LLDB command map

Source: https://lldb.llvm.org/use/map.html
GDBLLDBNotes
run [args]
process launch [args]
/ 
r
continue
process continue
/ 
c
next
thread step-over
/ 
n
step
thread step-in
/ 
s
nexti
thread step-inst-over
/ 
ni
stepi
thread step-inst
/ 
si
finish
thread step-out
/ 
finish
break main
breakpoint set -n main
/ 
b main
break file.c:42
breakpoint set -f file.c -l 42
/ 
b file.c:42
break *0x400abc
breakpoint set -a 0x400abc
/ 
b -a 0x400abc
watch x
watchpoint set variable x
/ 
wa s v x
print x
frame variable x
/ 
p x
print/x x
p/x x
info locals
frame variable
/ 
fr v
info args
frame variable --arguments
backtrace
thread backtrace
/ 
bt
frame N
frame select N
/ 
f N
info threads
thread list
thread N
thread select N
thread apply all bt
thread backtrace all
x/10wx addr
memory read -s4 -fx -c10 addr
/ 
x/10xw addr
set var = 42
expression var = 42
/ 
expr var = 42
quit
quit
/ 
q

3. Breakpoints

lldb
# By name
b main
breakpoint set --name foo
breakpoint set --name foo --condition 'x > 0'

# By file:line
b file.c:42
breakpoint set --file file.c --line 42

# By address
b -a 0x100003f20

# By regex
breakpoint set --func-regex '^MyClass::'

# List
breakpoint list / br l

# Delete
breakpoint delete 2

# Disable/enable
breakpoint disable 1
breakpoint enable 1

# Commands on hit
breakpoint command add 1
  > p x
  > continue
  > DONE

4. Inspect state

lldb
# Print variable
p x
frame variable x
p *ptr
p arr[0]

# Print expression
expression x * 2 + 1
expr (int)sqrt(9.0)

# All locals
frame variable
fr v -a          # include arguments

# Registers
register read
register read rip rsp

# Memory
memory read --size 4 --format x --count 10 0x7fff0000
x/10xw 0x7fff0000          # GDB-compatible syntax

# Type info
image lookup --type MyClass
type lookup MyClass

5. Watchpoints

lldb
watchpoint set variable x           # write watchpoint
watchpoint set variable -w read x   # read watchpoint
watchpoint set variable -w read_write x
watchpoint set expression -- &x     # by address

watchpoint list
watchpoint delete 1

6. Threads

lldb
thread list
thread select 3
thread backtrace all
thread backtrace --count 5           # limit depth

# Per-thread stepping
thread step-over                     # step this thread only

7. macOS / Apple specifics

lldb
# Symbol lookup in shared cache
image lookup --address 0x18ab12345
image lookup --name objc_msgSend

# Objective-C method breakpoint
b "-[NSArray objectAtIndex:]"
b "+[NSString stringWithFormat:]"

# Inspect Objective-C object
po myObject                          # print-object (calls -description)
po [arr count]

# Show loaded libraries
image list
image list -b                        # brief (names only)

8. VS Code integration

Install the 
CodeLLDB
extension. 
.vscode/launch.json
:
json
{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "Debug (lldb)",
      "type": "lldb",
      "request": "launch",
      "program": "${workspaceFolder}/build/prog",
      "args": [],
      "cwd": "${workspaceFolder}",
      "preLaunchTask": "build"
    }
  ]
}

9. LLDB Python scripting

python
import lldb

def print_all_threads(debugger, command, result, internal_dict):
    target = debugger.GetSelectedTarget()
    process = target.GetProcess()
    for thread in process:
        print(f"Thread {thread.GetIndexID()}: {thread.GetName()}")
        for frame in thread:
            print(f"  {frame}")

def __lldb_init_module(debugger, internal_dict):
    debugger.HandleCommand('command script add -f myscript.print_all_threads pthreads')
Load: 
command script import /path/to/myscript.py
For a full GDB↔LLDB command map, see references/gdb-lldb-map.md.

Related skills

  • Use 
    skills/debuggers/gdb
    for GDB workflows
  • Use 
    skills/debuggers/core-dumps
    for core dump analysis
  • Use 
    skills/compilers/clang
    for building with debug info