harvard.cs50.debug

Usage

This plugin adds Cloud9 commands that allow execution of the debugger from the command line.

gdb50{start,stop}

The gdb50start and gdb50stop commands try to allow the user to execute their binary directly in a terminal window, but still connect the GUI debugger to the running process without opening a new console window.

They use the existing run and debug system where possible, but provide an extraneous process to satisfy their requirements. In particular, run.gui normally expects a command to be executed, creates a new tmux session for it, and opens a new console window showing that tmux session with a lot of chrome describing the runner used to begin the process.

However, run.run allows us to run a command in a new tmux session and expects us to display it to the user. We simply chose not to display it, since the output of the executable is already being shown in the user's terminal.

The run system monitors this session for consistent state, so we get around the issue by providing a process that effectively acts as a proxy for the process we're running in the existing terminal. This "proxy" simply monitors the PID of the GDB shim, and destroys itself within ~1 second of when the shim quits.

The internal state of the process object (and therefore the run and debug objects) can then stay consistent.

Process management is therefore required for this to work. We create a process in the shell, provide the PID of that process to gdb50start, which then creates the "proxy" process to monitor it. If everything checks out, the plugin sends debug50 a SIGUSR1 signal, which then uses that to start the shim process.

This signal prevents starting the shim prematurely; for example, if the user selects when asked that they do not wish to stop an existing debug process.

If the shim is begun, gdb50stop is called after debugging is complete, and provided the same PID, to clean up the tmux session and process and debug object state.

To use this, simply call debug50, which is installed in ~/.cs50/bin (and should be in the $PATH by default):

$ debug50 BIN [ARGS]