Gdb

mohitmishra786/low-level-dev-skills/skills/debuggers/gdb

by mohitmishra786bdc58472fa9fNo license253 starsListed Oct 9, 2026Updated Oct 9, 2026Repository updated 3 months ago

GDB debugger skill for C/C++ programs. Use when starting a GDB session, setting breakpoints, stepping through code, inspecting variables, debugging crashes, using reverse debugging (record/replay), remote debugging with gdbserver, or loading core dumps. Activates on queries about GDB commands, segfaults, hangs, watchpoints, conditional breakpoints, pretty-printers, Python GDB scripting, or multi-threaded debugging.

Instructions onlySoftware Development
AI-generated overview

Guides agents through GDB debugging of C/C++ programs, from breakpoints and crash diagnosis to reverse and remote debugging.

What it does
This skill provides a structured walkthrough of GDB sessions for C/C++ programs. It covers compiling with debug info, starting GDB, essential stepping and inspection commands, breakpoints and watchpoints, multi-thread debugging, reverse debugging with record and replay, remote debugging via gdbserver, and common failure symptoms with fixes. It also points to reference documents on a command cheatsheet and on pretty-printers and Python scripting.
When to use it
Use it when a C/C++ program crashes, segfaults, hangs, or shows missing symbols and you need to debug it with GDB. It also fits setting breakpoints or watchpoints, inspecting variables, memory, registers, or threads, replaying a bug deterministically, debugging a remote or embedded target, or loading a core dump.
Requirements
No scripts are shipped; it is instructions plus two reference documents. Using the described workflows requires a GDB installation, a C/C++ toolchain such as GCC or Clang, and for remote debugging gdbserver on the target and network access between host and target.

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.c

For release builds: use -g -O2 and keep the binary with symbols (strip separately with objcopy).

2. Start GDB

bash
gdb ./prog                          # load binarygdb ./prog core                     # load with core dumpgdb -p 12345                        # attach to running processgdb --args ./prog arg1 arg2         # pass argumentsgdb -batch -ex 'run' -ex 'bt' ./prog  # non-interactive (CI)

3. Essential commands

CommandShortcutEffect
run [args]rStart the program
continuecResume after break
nextnStep over (source line)
stepsStep into
nextiniStep over (instruction)
stepisiStep into (instruction)
finishRun to end of current function
until NRun to line N
return [val]Force return from function
quitqExit GDB

4. Breakpoints and watchpoints

gdb
break main                          # break at functionbreak file.c:42                     # break at linebreak *0x400abc                     # break at addressbreak foo if x > 10                 # conditional breaktbreak foo                          # temporary breakpoint (fires once)rbreak ^mylib_.*                    # regex breakpoint on all matching functions
watch x                             # watchpoint: break when x changeswatch *(int*)0x601060               # watch memory addressrwatch x                            # break when x is readawatch x                            # break on read or write
info breakpoints                    # list all breakpointsdelete 3                            # delete breakpoint 3disable 3                           # disable without deletingenable 3

5. Inspect state

gdb
print x                             # print variableprint/x x                           # print in hexprint *ptr                          # dereference pointerprint arr[0]@10                     # print 10 elements of arraydisplay x                           # auto-print x on every stopundisplay 1
info locals                         # all local variablesinfo args                           # function argumentsinfo registers                      # all CPU registersinfo registers rip rsp rbp          # specific registersx/10wx 0x7fff0000                   # examine 10 words at addressx/s 0x400abc                        # examine as stringx/i $rip                            # examine current instruction
backtrace                           # call stack (bt)bt full                             # bt + local varsframe 2                             # switch to frame 2up / down                           # move up/down the stack

6. Multi-thread debugging

gdb
info threads                        # list threadsthread 3                            # switch to thread 3thread apply all bt                 # backtrace all threadsthread apply all bt full            # full bt all threadsset scheduler-locking on            # pause other threads while stepping

7. Reverse debugging (record/replay)

Record requires target record-full or target record-btrace (Intel PT):

gdb
# Software record (slow but universal)record                              # start recordingrun# ... trigger the bug ...reverse-continue                    # go back to last breakreverse-next                        # step backwardsreverse-stepreverse-finish
# Intel Processor Trace (fast, hardware)target record-btrace ptrun# view instruction historyrecord instruction-history

8. Remote debugging with gdbserver

On target:

bash
gdbserver :1234 ./prog# Or attach:gdbserver :1234 --attach 5678

On host:

bash
gdb ./prog(gdb) target remote 192.168.1.10:1234(gdb) break main(gdb) continue

For cross-compilation: use aarch64-linux-gnu-gdb on the host.

9. Common problems

SymptomCauseFix
No symbol tableBinary not compiled with -gRecompile with -g
?? frames in backtraceMissing debug info or stack corruptionInstall debuginfo package; check for stack smash
Cannot access memory at addressNull dereference / freed memoryCheck pointer before deref; use ASan
SIGABRT in backtraceabort() or assertion failureGo up frames to find the assertion
GDB hangs on runBinary waiting for inputRedirect stdin: run < /dev/null
Breakpoint in wrong placeOptimiser moved codeCompile with -Og; or use nexti

10. GDB init file (~/.gdbinit)

gdb
set history save onset history size 1000set print pretty onset print array onset print array-indexes onset pagination offset confirm off

For a command cheatsheet, see references/cheatsheet.md [blocked]. For pretty-printers and Python scripting, see references/scripting.md [blocked].

Related skills

  • Use skills/debuggers/core-dumps for loading core files
  • Use skills/debuggers/lldb for LLDB-based workflows
  • Use skills/runtimes/sanitizers to catch bugs before needing the debugger
  • Use skills/compilers/gcc for -g flag details

Source and attribution

Source:mohitmishra786/low-level-dev-skillsinskills/debuggers/gdbat commitbdc5847

License: No license

Content belongs to its original authors. SourceWeft indexes it from a public repository.

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