How to use
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npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill lldbBefore you start
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Original skill document
Rendered from the source repository. Headings, examples, code, tables, links, and referenced images are preserved.
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 + core2. GDB → LLDB command map
Source: <https://lldb.llvm.org/use/map.html>
| GDB | LLDB | Notes |
|---|---|---|
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
> DONE4. 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 MyClass5. 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 16. 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 only7. 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/gdbfor GDB workflows - Use
skills/debuggers/core-dumpsfor core dump analysis - Use
skills/compilers/clangfor building with debug info
