gdb: GNU Debugger

Overview

gdb provides in-depth debugging capabilities, allowing you to control program execution flow, inspect variable values, and examine memory states. It is particularly useful for analyzing issues in compiled binary files.

Key Features

Start/stop a running program
Set breakpoints
Inspect and modify variable values
View stack traces
Examine memory contents
Analyze core files

Key Options

gdb is primarily used in interactive mode, but you can also use specific options at startup to configure initial settings or run non-interactive scripts.

Startup/Connection Options

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Usage Examples

Since gdb is often used interactively, the examples include commands entered within the gdb prompt.

Start a Basic Debugging Session

gdb ./my_program

Load a compiled program (e.g., my_program) into gdb to start a debugging session.

Set Breakpoint and Run

gdb ./my_program
(gdb) b main
(gdb) r

Set a breakpoint at the main function and run the program. Execution will stop at the breakpoint.

Inspect Variable Value

gdb ./my_program
(gdb) b my_function
(gdb) r
(gdb) p my_variable

After stopping at a breakpoint, print the current value of a specific variable.

Analyze Core File

gdb ./my_program core.dump

Analyze a core file generated by a program crash to examine the program's state at the time of the crash.

Attach to a Running Process

gdb -p 12345

Attach gdb to a running process with PID 12345 for debugging.

Automatically Execute Commands on Startup

gdb -ex 'b main' -ex 'r' ./my_program

Set a breakpoint at the main function and run the program immediately upon gdb startup.

Installation

gdb is not provided by default on most Linux distributions and needs to be installed as part of the development tools package.

Debian/Ubuntu

sudo apt update && sudo apt install gdb

Install gdb using the APT package manager.

Fedora/CentOS/RHEL

sudo dnf install gdb

Install gdb using the DNF or YUM package manager.

Tips & Notes

Tips and notes for effectively using gdb.

Include Debugging Information During Compilation

To debug with gdb, you must compile your program with the `-g` option to include debugging information. Otherwise, you won't be able to see source code information or variable names.

Example: `gcc -g myprogram.c -o myprogram`

Frequently Used gdb Commands

Core commands frequently used within the gdb prompt.

`b <function_name/line_number>`: Set breakpoint
`r`: Run the program
`n`: Step to the next line (next)
`s`: Step into a function (step)
`p <variable_name>`: Print variable value
`c`: Continue execution until the next breakpoint
`q`: Quit gdb

Utilize TUI Mode

Using gdb's Text User Interface (TUI) mode can enhance debugging efficiency by allowing you to view source code, registers, and assembly simultaneously.

Use `gdb -tui <program>` or the `layout src` command within gdb.