Mode d’emploi
- Copiez la commande et examinez le paquet avant de l’installer dans votre environnement agent.
- Consultez le document original pour les outils, identifiants et environnements requis.
- Décrivez les entrées et le livrable souhaité ; comparez la sortie aux sources.
npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill gdbAvant de commencer
- L’installation n’inclut ni abonnement au modèle, ni quota API, ni accès aux fichiers.
- Étoiles et installations reflètent l’activité, pas un test indépendant de qualité ou de sécurité.
Document Skill original
Rendu depuis le dépôt source en conservant titres, exemples, code, tableaux, liens et images.
GDB
Purpose
Walk agents through GDB sessions from first launch to advanced workflows: crash diagnosis, reverse debugging, remote debugging, and multi-thread inspection.
Triggers
- "My program segfaults / crashes — how do I debug it?"
- "How do I set a breakpoint on condition X?"
- "How do I inspect memory / variables in GDB?"
- "How do I debug a remote embedded target?"
- "GDB shows
??frames / no source" - "How do I replay a bug deterministically?" (record/replay)
Workflow
1. Prerequisite: compile with debug info
Always compile with -g (GCC/Clang). Use -Og or -O0 for most debuggable code.
bash
gcc -g -Og -o prog main.cFor release builds: use -g -O2 and keep the binary with symbols (strip separately with objcopy).
2. Start GDB
bash
gdb ./prog # load binary
gdb ./prog core # load with core dump
gdb -p 12345 # attach to running process
gdb --args ./prog arg1 arg2 # pass arguments
gdb -batch -ex 'run' -ex 'bt' ./prog # non-interactive (CI)3. Essential commands
| Command | Shortcut | Effect |
|---|---|---|
run [args] | r | Start the program |
continue | c | Resume after break |
next | n | Step over (source line) |
step | s | Step into |
nexti | ni | Step over (instruction) |
stepi | si | Step into (instruction) |
finish | Run to end of current function | |
until N | Run to line N | |
return [val] | Force return from function | |
quit | q | Exit GDB |
4. Breakpoints and watchpoints
gdb
break main # break at function
break file.c:42 # break at line
break *0x400abc # break at address
break foo if x > 10 # conditional break
tbreak foo # temporary breakpoint (fires once)
rbreak ^mylib_.* # regex breakpoint on all matching functions
watch x # watchpoint: break when x changes
watch *(int*)0x601060 # watch memory address
rwatch x # break when x is read
awatch x # break on read or write
info breakpoints # list all breakpoints
delete 3 # delete breakpoint 3
disable 3 # disable without deleting
enable 35. Inspect state
gdb
print x # print variable
print/x x # print in hex
print *ptr # dereference pointer
print arr[0]@10 # print 10 elements of array
display x # auto-print x on every stop
undisplay 1
info locals # all local variables
info args # function arguments
info registers # all CPU registers
info registers rip rsp rbp # specific registers
x/10wx 0x7fff0000 # examine 10 words at address
x/s 0x400abc # examine as string
x/i $rip # examine current instruction
backtrace # call stack (bt)
bt full # bt + local vars
frame 2 # switch to frame 2
up / down # move up/down the stack6. Multi-thread debugging
gdb
info threads # list threads
thread 3 # switch to thread 3
thread apply all bt # backtrace all threads
thread apply all bt full # full bt all threads
set scheduler-locking on # pause other threads while stepping7. Reverse debugging (record/replay)
Record requires target record-full or target record-btrace (Intel PT):
gdb
# Software record (slow but universal)
record # start recording
run
# ... trigger the bug ...
reverse-continue # go back to last break
reverse-next # step backwards
reverse-step
reverse-finish
# Intel Processor Trace (fast, hardware)
target record-btrace pt
run
# view instruction history
record instruction-history8. Remote debugging with gdbserver
On target:
bash
gdbserver :1234 ./prog
# Or attach:
gdbserver :1234 --attach 5678On host:
bash
gdb ./prog
(gdb) target remote 192.168.1.10:1234
(gdb) break main
(gdb) continueFor cross-compilation: use aarch64-linux-gnu-gdb on the host.
9. Common problems
| Symptom | Cause | Fix |
|---|---|---|
No symbol table | Binary not compiled with -g | Recompile with -g |
?? frames in backtrace | Missing debug info or stack corruption | Install debuginfo package; check for stack smash |
Cannot access memory at address | Null dereference / freed memory | Check pointer before deref; use ASan |
SIGABRT in backtrace | abort() or assertion failure | Go up frames to find the assertion |
GDB hangs on run | Binary waiting for input | Redirect stdin: run < /dev/null |
| Breakpoint in wrong place | Optimiser moved code | Compile with -Og; or use nexti |
10. GDB init file (~/.gdbinit)
gdb
set history save on
set history size 1000
set print pretty on
set print array on
set print array-indexes on
set pagination off
set confirm offFor a command cheatsheet, see references/cheatsheet.md. For pretty-printers and Python scripting, see references/scripting.md.
Related skills
- Use
skills/debuggers/core-dumpsfor loading core files - Use
skills/debuggers/lldbfor LLDB-based workflows - Use
skills/runtimes/sanitizersto catch bugs before needing the debugger - Use
skills/compilers/gccfor-gflag details
