B.4 The GNU Debugger (gdb)

The following tables list some useful commands of the GNU Debugger (gdb). For a complete list of available commands, see the gdb online documentation.^[94]

Starting and Stopping gdb

Command	Description
gdb program	Starts gdb with program to debug.
quit	Exits the debugger.

General Commands

Command	Description
run arguments	Starts debugged program (with arguments).
attach processID	Attaches the debugger to the running process with processID.

Breakpoints

Command	Description
break <file:> function	Sets a breakpoint at the beginning of the specified function (in file).
break <file:> line number	Sets a breakpoint at the start of the code for that line number (in file).
break *address	Sets a breakpoint at the specified address.
info breakpoints	Lists information about existing breakpoints.
delete number	Removes previously set breakpoints specified by their number.

Running the Debuggee

Command	Description
stepi	Executes one machine instruction. Will step into subfunctions.
nexti	Executes one machine instruction. Will not enter subfunctions.
continue	Resumes execution.

Examining Data

Command	Description
x/CountFormatSize address	Prints the specified number of objects (Count) of the specified Size according to the Format at address. Size: b (byte), h (halfword), w (word), g (giant, 8 bytes). Format: o (octal), x (hexadecimal), d (decimal), u (unsigned decimal), t (binary), f (float), a (address), i (instruction), c (char), s (string).

Information Commands

Command	Description
info registers	Lists registers and their contents.
backtrace	Prints a backtrace of all stack frames.
disassemble address	Dumps a range of memory around address as machine instructions.

Other Commands

Command	Description
set disassembly-flavor intel|att	Sets the disassembly flavor to Intel or AT&T assembly syntax. Default is AT&T syntax.
shell command	Executes a shell command.
set variable *(address)=value	Stores value at the memory location specified by address.
source file	Reads debugger commands from a file.
set follow-fork-mode parent|child	Tells the debugger to follow the child or parent process.