PDR: Docs: GDB Command Summary

Go up to the main documents page (md)

Assembly-specific commands

• stepi: step one MACHINE instruction (i.e. assembly instruction), instead of one C++ instruction (which is what step does)
• info registers: display the values in the registers
• set disassembly-flavor intel: set the assembly output format to what we are used to in class (and what we are programming in)
• disassemble: like list, but displays the lines of assembly code currently being executed.
• disassemble (function): prints the assembly code for the supplied function (up until the next label)

Program execution

• run: starts a program execution, and continues until it exits, crashes, or hits a breakpoint
• start: starts a program execution, and breaks when it enters the main() function
• bt: prints a back trace, which is the list of function calls that got to the current point
• list: shows the lines of source code before and after the point at which the program paused
• list (function): prints the lines of code around (function) or the current breakpoint otherwise if no (function) is provided.
• up: move up the back trace function stack list
• down: move down the back trace function stack list
• step (or just s): step INTO the next line of code to execute
• next (or just n): step OVER the next line of code to execute
• continue (or just c): continue execution
• finish: finishes executing the current function and then pauses
• quit: exits the debugger

Breakpoints

• b (pos) (or break (pos)): set a breakpoint at (pos). A breakpoint can be a function name (e.g., b GetMax), a line number (e.g., b 22), or either of the above preceded by a file name (e.g., b lab2.cpp:22 or b lab2.cpp:GetMax)
• tbreak (pos): set a temporary breakpoint (only breaks the first time)
• info break: show breakpoints
• delete (or just d): deletes all breakpoints
• delete (num): delete the breakpoint indicated by (num)

Examining data

• print (var) (or p): print the value in the given variable
• print &(var): print the address that the given variable is located
• print *(ptr): print the destination of a pointer
• x/(format) (var/address): format controls how the memory should be displayed, and consists of (up to) 3 components: a numeric count of how many elements to display; a single-character format, indicating how to interpret and display each element – e.g. a few of the flags are x/x displays in hex, x/d displays in signed decimals, x/c displays in characters, x/i displays in instructions, and x/s displays in C strings; and a single-character size, indicating the size of each element to display – e.g. b, h, w, and g, for one-, two-, four-, and eight-byte blocks, respectively. You can have multiple at a time, e.g. x/30x (var/address) will display 30 elements in hexidecimal from the provided var/address OR if no var/address is provided, from the top of the stack.
• info locals: display all the local variables and their values
• display (var): always display the value in (var) whenever the program pauses
• display: show the variables that have been entered with display and their numeric IDs
• undisplay (num): stop displaying the variable with numeric ID num
• print function_call(params): execute the function, and print the result
• set variable (var) = (value): set the variable (var) to the value (value) – e.g. set variable foo = 5
• frame x: moves to frame x in the backtrace (bt) of a crashed or paused program