Advanced GDB Cheat Sheet (threading)

gdb-thread.md

GDB Threading Cheat Sheet

Designed for multi-threaded, multi-process, and advanced use cases. Convert with:

pandoc -o gdb-advanced.odt gdb-advanced.md

and play with the odt until happy, then export as .pdf.

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Threads & Concurrency

Command	Description
info threads	List threads with IDs, states, top frame.
thread <n>	Switch to thread n.
thread apply all bt full	Backtrace for all threads with locals (deadlock detection).
info thread <n>	Detailed info about thread n.
info threads -full	More verbose thread info (needs libthread_db).
set scheduler-locking step	Step only current thread (freeze others).
info tasks	Show Linux tasks (kernel threads) if supported.
monitor info threads	Extra info with gdbserver/remote.
info pthread (glibc)	Show pthread structures (if available).

Deadlock check:

1. info threads – see which threads are waiting.
2. thread apply all bt full – look for pthread_mutex_lock, futex_wait.
3. Correlate owner TIDs from mutex structs to thread TIDs.

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Processes & Fork/Exec

Command	Description
`set follow-fork-mode parent	child`
`set detach-on-fork on	off`
info inferiors	List processes (inferiors) under GDB.
inferior <n>	Switch between inferiors.
add-inferior	Add empty inferior slot (multi-process debugging).
clone-inferior <n>	Duplicate state of inferior n.
detach inferior <n>	Detach process n.

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Watchpoints & Advanced Breakpoints

Command	Description
watch <expr>	Break when expr changes.
rwatch <expr>	Break when expr is read.
awatch <expr>	Break on read or write.
catch fork	Break on fork().
catch exec	Break on exec().
catch syscall <n>	Break on syscall number n.
catch throw / catch catch	Break on C++ exception throw/catch.
break if <cond>	Conditional breakpoint.
commands <n>	Define actions when breakpoint n triggers.

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Signals

Command	Description
`handle print	ignore
info signals	List signals and handling status.
signal <sig>	Send signal to program.
catch signal	Break when program receives a signal.

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Expressions & Data

Command	Description
print /x <expr>	Print in hex.
ptype <expr>	Show type.
whatis <expr>	Shorthand type query.
set var <expr>=<val>	Assign variable.
call <func>(args)	Call function manually.
print *(type*)addr	Cast and dereference memory.
x/<nfu> <addr>	Examine memory (n=count, f=format, u=unit).
set print pretty on	Pretty-print arrays/structs.
set print elements 0	Don’t truncate long arrays.

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Advanced Navigation

Command	Description
tui enable	Enable TUI (text UI) mode.
`layout src	asm
`focus src	asm
disassemble /m <func>	Mixed source/assembly view.
record / record full	Start process recording.
reverse-continue	Run backward in record mode.
reverse-step / reverse-next	Step backward.

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Remote Debugging & Core Files

Command	Description
target remote <host:port>	Connect to gdbserver.
target extended-remote <...>	Extended remote mode.
monitor <cmd>	Send raw command to gdbserver.
set sysroot <path>	Point to target system libraries.
core <corefile>	Load a core dump.
info files	Show loaded executable and symbols.

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Scripting & Automation

Command	Description
source <file>	Run GDB script.
define <cmd>	Define a custom command.
document <cmd>	Add help text to your custom command.
python ... end	Inline Python scripting.
set logging on	Log session to gdb.txt.
macro expand <expr>	Expand C macros.
macro define	Define C macros inside GDB.

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Mutex Ownership & Deadlock Helpers

Command / Tool	Description
print *(pthread_mutex_t *)<ptr>	Inspect mutex struct; look at __data.__owner for owning TID (glibc).
info threads	Match owner TID to GDB thread number.
thread apply all bt full	Full stacks to find blockers/waiters.

gdb-pthread-utils (Python extension)

github.com/gbpthreads/gdb-pthread-utils

Command (after loading plugin)	Description
pthread info mutex <ptr>	Pretty-print mutex state and owner thread.
pthread info all-mutexes	Show all known mutexes and their owners.
pthread info cond <ptr>	Show condition variable waiters.

Load plugin:

source /path/to/gdb-pthread-utils.py

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Popular GDB Python Extensions

Extension	URL / Source	What It Adds
gdb-peda	github.com/longld/peda	Enhanced disassembly, registers, shellcode tools.
pwndbg	github.com/pwndbg/pwndbg	Modern replacement for PEDA; better heap/threads view.
GEF	github.com/hugsy/gef	Modular enhancement for reverse-engineering/exploit dev.
voltron	github.com/snare/voltron	External TUI panels in your terminal.
libheap	github.com/cloudburst/libheap	Heap debugging for glibc (malloc/free).
gdb-pthread-utils	github.com/gbpthreads/gdb-pthread-utils	Pretty-print pthread mutexes/conds, show owners/waiters.
gdb-dashboard	github.com/cyrus-and/gdb-dashboard	Dashboard with registers, stack, source, breakpoints.
rr + gdb	rr-project.org	Record/replay debugging with reverse execution.

Loading an extension:

source /path/to/plugin.py

Some provide installers:

git clone https://github.com/pwndbg/pwndbg
cd pwndbg && ./setup.sh

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Tip: Use tab completion and help <command> inside GDB for details.