Appendix A: LLDB for GDB Users – Command Summary

LLDB is the supported engine underlying all debugging operations for use with Xcode and all officially distributed Apple development products. Some users who are new to Xcode might be more familiar with GDB commands. By default, LLDB contains a library of aliases modeled on GDB commands in order to ease getting started.

The tables in this appendix list commonly used GDB commands, presenting equivalent LLDB commands and alternative forms. Also listed are the built-in GDB compatibility aliases in LLDB.

Execution Commands

GDB

LLDB

Launch a process with no arguments

(gdb) run

(gdb) r

(lldb) process launch

(lldb) run

(lldb) r

Launch a process with arguments <args>

(gdb) run <args>

(gdb) r <args>

(lldb) process launch -- <args>

(lldb) r <args>

Launch process a.out with arguments 1 2 3 without having to supply the args every time

% gdb --args a.out 1 2 3

(gdb) run

...

(gdb) run

...

(% lldb -- a.out 1 2 3

(lldb) run

...

(lldb) run

...

Launch a process with arguments in a new terminal window (OS X only)

 —

(lldb) process launch --tty -- <args>

(lldb) pro la -t -- <args>

Launch a process with arguments in an existing Terminal window, /dev/ttys006 (OS X only)

 —

(lldb) process launch --tty=/dev/ttys006 -- <args>

(lldb) pro la -t/dev/ttys006 -- <args>

Set environment variables for process before launching

(gdb) set env DEBUG 1

(lldb) settings set target.env-vars DEBUG=1

(lldb) set se target.env-vars DEBUG=1

Set environment variables for process and launch process in one command

 

(lldb) process launch -v DEBUG=1

Attach to the process with process ID 123

(gdb) attach 123

(lldb) process attach --pid 123

(lldb) attach -p 123

Attach to a process named a.out

(gdb) attach a.out

(lldb) process attach --name a.out

(lldb) pro at -n a.out

Wait for a process named a.out to launch and attach

(gdb) attach -waitfor a.out

(lldb) process attach --name a.out --waitfor

(lldb) pro at -n a.out -w

Attach to a remote GDB protocol server running on the system eorgadd, port 8000

(gdb) target remote eorgadd:8000

(lldb) gdb-remote eorgadd:8000

Attach to a remote GDB protocol server running on the local system, port 8000

(gdb) target remote localhost:8000

(lldb) gdb-remote 8000

Attach to a Darwin kernel in kdp mode on the system eorgadd

(gdb) kdp-reattach eorgadd

(lldb) kdp-remote eorgadd

Do a source-level single step in the currently selected thread

(gdb) step

(gdb) s

(lldb) thread step-in

(lldb) step

(lldb) s

Do a source-level single step over in the currently selected thread

(gdb) next

(gdb) n

(lldb) thread step-over

(lldb) next

(lldb) n

Do an instruction-level single step in the currently selected thread

(gdb) stepi

(gdb) si

(lldb) thread step-inst

(lldb) si

Do an instruction-level single step over in the currently selected thread

(gdb) nexti

(gdb) ni

(lldb) thread step-inst-over

(lldb) ni

Step out of the currently selected frame

(gdb) finish

(lldb) thread step-out

(lldb) finish

Backtrace and disassemble every time you stop

 —

(lldb) target stop-hook add

Enter your stop hook command(s). Type 'DONE' to end.

> bt

> disassemble --pc

> DONE

Stop hook #1 added.

Breakpoint Commands

GDB

LLDB

Set a breakpoint at all functions named main

(gdb) break main

(lldb) breakpoint set --name main

(lldb) br s -n main

(lldb) b main

Set a breakpoint in file test.c at line 12

(gdb) break test.c:12

(lldb) breakpoint set --file test.c --line 12

(lldb) br s -f test.c -l 12

(lldb) b test.c:12

Set a breakpoint at all C++ methods whose basename is main

(gdb) break main

(Note: This will break on any C functions named main.)

(lldb) breakpoint set --method main

(lldb) br s -M main

Set a breakpoint at an Objective-C function: -[NSString stringWithFormat:]

(gdb) break -[NSString stringWithFormat:]

(lldb) breakpoint set --name "-[NSString stringWithFormat:]"

(lldb) b -[NSString stringWithFormat:]

Set a breakpoint at all Objective-C methods whose selector is count

(gdb) break count

(Note: This will break on any C or C++ functions named count.)

(lldb) breakpoint set --selector count

(lldb) br s -S count

Set a breakpoint by a regular expression on a function name

(gdb) rbreak regular-expression

(lldb) breakpoint set --regex regular-expression

(lldb) br s -r regular-expression

Set a breakpoint by a regular expression on a source file’s contents

(gdb) shell grep -e -n pattern source-file

(gdb) break source-file:CopyLineNumbers

(lldb) breakpoint set --source-pattern regular-expression --file SourceFile

(lldb) br s -p regular-expression -f file

List all breakpoints

(gdb) info break

(lldb) breakpoint list

(lldb) br l

Delete a breakpoint

(gdb) delete 1

(lldb) breakpoint delete 1

(lldb) br del 1

Watchpoint Commands

GDB

LLDB

Set a watchpoint on a variable when it is written to

(gdb) watch global_var

(lldb) watchpoint set variable global_var

(lldb) wa s v global_var

Set a watchpoint on a memory location when it is written to

(gdb) watch -location g_char_ptr

(lldb) watchpoint set expression -- my_ptr

(lldb) wa s e -- my_ptr

 

Note: The size of the region to watch for defaults to the pointer size if no -x byte_size is specified. This command takes “raw” input, evaluated as an expression returning an unsigned integer pointing to the start of the region, after the option terminator (--).

Set a condition on a watchpoint

 —

(lldb) watch set var global

(lldb) watchpoint modify -c '(global==5)'

(lldb) c

...

(lldb) bt

* thread #1: tid = 0x1c03, 0x0000000100000ef5 a.out`modify + 21 at main.cpp:16, stop reason = watchpoint 1

frame #0: 0x0000000100000ef5 a.out`modify + 21 at main.cpp:16

frame #1: 0x0000000100000eac a.out`main + 108 at main.cpp:25

frame #2: 0x00007fff8ac9c7e1 libdyld.dylib`start + 1

(int32_t) global = 5

List all watchpoints

(gdb) info break

(lldb) watchpoint list

(lldb) watch l

Delete a watchpoint

(gdb) delete 1

(lldb) watchpoint delete 1

(lldb) watch del 1

Examining Variables

GDB

LLDB

Show the arguments and local variables for the current frame

(gdb) info args

and

(gdb) info locals

(lldb) frame variable

(lldb) fr v

Show the local variables for the current frame

(gdb) info locals

(lldb) frame variable --no-args

(lldb) fr v -a

Show the contents of the local variable bar

(gdb) p bar

(lldb) frame variable bar

(lldb) fr v bar

(lldb) p bar

Show the contents of the local variable bar formatted as hex

(gdb) p/x bar

(lldb) frame variable --format x bar

(lldb) fr v -f x bar

Show the contents of the global variable baz

(gdb) p baz

(lldb) target variable baz

(lldb) ta v baz

Show the global/static variables defined in the current source file

 —

(lldb) target variable

(lldb) ta v

Display the variables argc and argv every time you stop

(gdb) display argc

(gdb) display argv

(lldb) target stop-hook add --one-liner "frame variable argc argv"

(lldb) ta st a -o "fr v argc argv"

(lldb) display argc

(lldb) display argv

Display the variables argc and argv only when you stop in the function named main

 —

 

(lldb) target stop-hook add --name main --one-liner "frame variable argc argv"

(lldb) ta st a -n main -o "fr v argc argv"

Display the variable *this only when you stop in the C class named MyClass

 —

 

(lldb) target stop-hook add --classname MyClass --one-liner "frame variable *this"

(lldb) ta st a -c MyClass -o "fr v *this"

Evaluating Expressions

GDB

LLDB

Evaluate a generalized expression in the current frame

(gdb) print (int) printf ("Print nine: %d.", 4 + 5)

 

Or if you don’t want to see void returns:

(gdb) call (int) printf ("Print nine: %d.", 4 + 5)

(lldb) expr (int) printf ("Print nine: %d.", 4 + 5)

 

Or use the print alias:

(lldb) print (int) printf ("Print nine: %d.", 4 + 5)

Create and assign a value to a convenience variable

(gdb) set $foo = 5

(gdb) set variable $foo = 5

 

Or use the print command:

(gdb) print $foo = 5

 

Or use the call command:

(gdb) call $foo = 5

 

To specify the type of the variable:

(gdb) set $foo = (unsigned int) 5

LLDB evaluates a variable declaration expression as you would write it in C:

(lldb) expr unsigned int $foo = 5

Print the Objective-C description of an object

(gdb) po [SomeClass returnAnObject]

(lldb) expr -O -- [SomeClass returnAnObject]

 

Or use the po alias:

(lldb) po [SomeClass returnAnObject]

Print the dynamic type of the result of an expression

(gdb) set print object 1

(gdb) p someCPPObjectPtrOrReference

 

Note: Only for C++ objects.

(lldb) expr -d run-target -- [SomeClass returnAnObject]

(lldb) expr -d run-target -- someCPPObjectPtrOrReference

 

Or set dynamic type printing as default:

(lldb) settings set target.prefer-dynamic run-target

Call a function to stop at a breakpoint in the function

(gdb) set unwindonsignal 0

(gdb) p function_with_a_breakpoint()

(lldb) expr -u 0 -- function_with_a_breakpoint()

Examining Thread State

GDB

LLDB

Show the stack backtrace for the current thread

(gdb) bt

(lldb) thread backtrace

(lldb) bt

Show the stack backtraces for all threads

(gdb) thread apply all bt

(lldb) thread backtrace all

(lldb) bt all

Backtrace the first five frames of the current thread

(gdb) bt 5

(lldb) thread backtrace -c 5

(lldb) bt 5 (lldb-169 and later)

(lldb) bt -c 5 (lldb-168 and earlier)

Select a different stack frame by index for the current thread

(gdb) frame 12

(lldb) frame select 12

(lldb) fr s 12

(lldb) f 12

List information about the currently selected frame in the current thread

 —

(lldb) frame info

Select the stack frame that called the current stack frame

(gdb) up

(lldb) up

(lldb) frame select --relative=1

Select the stack frame that is called by the current stack frame

(gdb) down

(lldb) down

(lldb) frame select --relative=-1

(lldb) fr s -r-1

Select a different stack frame using a relative offset

(gdb) up 2

(gdb) down 3

(lldb) frame select --relative 2

(lldb) fr s -r2

 

(lldb) frame select --relative -3

(lldb) fr s -r-3

Show the general-purpose registers for the current thread

(gdb) info registers

(lldb) register read

Write a new decimal value 123 to the current thread register rax

(gdb) p $rax = 123

(lldb) register write rax 123

Skip 8 bytes ahead of the current program counter (instruction pointer)

(gdb) jump *$pc+8

(lldb) register write pc `$pc+8`

 

The LLDB command uses backticks to evaluate an expression and insert the scalar result.

Show the general-purpose registers for the current thread formatted as signed decimal

 —

(lldb) register read --format i

(lldb) re r -f i

 

LLDB now supports the GDB shorthand format syntax, but no space is permitted after the command:

(lldb) register read/d

 

Note: LLDB tries to use the same format characters as printf(3) when possible. Type help format to see the full list of format specifiers.

Show all registers in all register sets for the current thread

(gdb) info all-registers

(lldb) register read --all

(lldb) re r -a

Show the values for the registers named rax, rsp and rbp in the current thread

(gdb) info all-registers rax rsp rbp

(lldb) register read rax rsp rbp

Show the values for the register named rax in the current thread formatted as binary

(gdb) p/t $rax

(lldb) register read --format binary rax

(lldb) re r -f b rax

 

LLDB now supports the GDB shorthand format syntax, but no space is permitted after the command:

(lldb) register read/t rax

(lldb) p/t $rax

Read memory from address 0xbffff3c0 and show four hex uint32_t values

(gdb) x/4xw 0xbffff3c0

(lldb) memory read --size 4 --format x --count 4 0xbffff3c0

(lldb) me r -s4 -fx -c4 0xbffff3c0

(lldb) x -s4 -fx -c4 0xbffff3c0

 

LLDB now supports the GDB shorthand format syntax, but no space is permitted after the command:

(lldb) memory read/4xw 0xbffff3c0

(lldb) x/4xw 0xbffff3c0

(lldb) memory read --gdb-format 4xw 0xbffff3c0

Read memory starting at the expression argv[0]

(gdb) x argv[0]

(lldb) memory read `argv[0]`

 

Note that any command can inline a scalar expression result (as long as the target is stopped) using back ticks (``) around any expression:

(lldb) memory read --size `sizeof(int)` `argv[0]`

Read 512 bytes of memory from address 0xbffff3c0 and save results to a local file as text

(gdb) set logging on

(gdb) set logging file /tmp/mem.txt

(gdb) x/512bx 0xbffff3c0

(gdb) set logging off

(lldb) memory read --outfile /tmp/mem.txt --count 512 0xbffff3c0

(lldb) me r -o/tmp/mem.txt -c512 0xbffff3c0

(lldb) x/512bx -o/tmp/mem.txt 0xbffff3c0

Save binary memory data to a file starting at 0x1000 and ending at 0x2000

(gdb) dump memory /tmp/mem.bin 0x1000 0x2000

(lldb) memory read --outfile /tmp/mem.bin --binary 0x1000 0x1200

(lldb) me r -o /tmp/mem.bin -b 0x1000 0x1200

Disassemble the current function for the current frame

(gdb) disassemble

(lldb) disassemble --frame

(lldb) di -f

Disassemble any functions named main

(gdb) disassemble main

(lldb) disassemble --name main

(lldb) di -n main

Disassemble an address range

(gdb) disassemble 0x1eb8 0x1ec3

(lldb) disassemble --start-address 0x1eb8 --end-address 0x1ec3

(lldb) di -s 0x1eb8 -e 0x1ec3

Disassemble 20 instructions from a given address

(gdb) x/20i 0x1eb8

(lldb) disassemble --start-address 0x1eb8 --count 20

(lldb) di -s 0x1eb8 -c 20

Show mixed source and disassembly for the current function for the current frame

 —

(lldb) disassemble --frame --mixed

(lldb) di -f -m

Disassemble the current function for the current frame and show the opcode bytes

 —

(lldb) disassemble --frame --bytes

(lldb) di -f -b

Disassemble the current source line for the current frame

 —

(lldb) disassemble --line

(lldb) di -l

Executable and Shared Library Query Commands

GDB

LLDB

List the main executable and all dependent shared libraries

(gdb) info shared

(lldb) image list

Look up information for a raw address in the executable or any shared libraries

(gdb) info symbol 0x1ec4

(lldb) image lookup --address 0x1ec4

(lldb) im loo -a 0x1ec4

Look up functions matching a regular expression in a binary

(gdb) info function <FUNC_REGEX>

This one finds debug symbols:

(lldb) image lookup -r -n <FUNC_REGEX>

 

This one finds non-debug symbols:

(lldb) image lookup -r -s <FUNC_REGEX>

 

Provide a list of binaries as arguments to limit the search.

Look up information for an address in a.out only

 —

(lldb) image lookup --address 0x1ec4 a.out

(lldb) im loo -a 0x1ec4 a.out

Look up information for a type Point by name

(gdb) ptype Point

(lldb) image lookup --type Point

(lldb) im loo -t Point

Dump all sections from the main executable and any shared libraries

(gdb) maintenance info sections

(lldb) image dump sections

Dump all sections in the a.out module

 —

(lldb) image dump sections a.out

Dump all symbols from the main executable and any shared libraries

 —

(lldb) image dump symtab

Dump all symbols in a.out and liba.so

 —

(lldb) image dump symtab a.out liba.so

Miscellaneous

GDB

LLDB

Echo text to the screen

(gdb) echo Here is some text\n

(lldb) script print "Here is some text"

Remap source file pathnames for the debug session

(gdb) set pathname-substitutions /buildbot/path /my/path

(lldb) settings set target.source-map /buildbot/path /my/path

 

Note: If your source files are no longer located in the same location as when the program was built—maybe the program was built on a different computer—you need to tell the debugger how to find the sources at the local file path instead of the build system file path.

Supply a catchall directory to search for source files in

(gdb) directory /my/path

(No equivalent command.)



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