By default, the debugger opens the file containing your program's executable code read-only. This prevents accidental alterations to machine code; but it also prevents you from intentionally patching your program's binary.
If you'd like to be able to patch the binary, you can specify that explicitly with the set write command. For example, you might want to turn on internal debugging flags, or even to make emergency repairs.
If you specify set write on, the debugger opens executable files for both reading and writing; if you specify set write off (the default), the debugger opens them read-only.
If you have already loaded a file, you must load it again (using the exec-file command) after changing set write, for your new setting to take effect.
Display whether executable files are opened for writing as well as reading.