GP-71: Prepping for source release.

Ghidra/Debug/Debugger-agent-gdb/src/main/resources/session.py

@@ -0,0 +1,62 @@
+#!/usr/bin/env python
+"""
+This script starts a new session on the given TTY
+
+The first parameter is the TTY file name. The remaining parameters
+specify the image path and parameters of the session leader process.
+
+A few stack overflow questions, the Linux man pages, and a good
+tutorial on TTYs, PTYs, jobs, process groups, and sessions is needed to
+understand everything that is going on here. Nevertheless, the
+operative lines are commented in the hopes it will help readers find
+their way.
+"""
+from __future__ import print_function
+
+import os
+import sys
+
+
+def main():
+    # Parse the arguments
+    ptypath = sys.argv[1]
+    args = sys.argv[2:]
+
+    try:
+        # This tells Linux to make this process the leader of a new session.
+        os.setsid()
+    except OSError as e:
+        # This error occurs if we are already a session leader. Unlikely....
+        print("Warning: setsid failed with EPERM")
+        if e.errno != 1:
+            raise e
+
+    # Open the TTY. On Linux, the first TTY opened since becoming a session
+    # leader becomes the session's controlling TTY. Other platforms, e.g., BSD
+    # may require an explicit IOCTL.
+    fd = os.open(ptypath, os.O_RDWR)
+
+    # Copy stderr to a backup descriptor, in case something goes wrong.
+    bk = fd + 1
+    os.dup2(2, bk)
+
+    # Copy the TTY fd over all standard streams. This effectively redirects
+    # the leader's standard streams to the TTY.
+    os.dup2(fd, 0)
+    os.dup2(fd, 1)
+    os.dup2(fd, 2)
+
+    # At this point, we are the session leader and the named TTY is the
+    # controlling PTY.
+    # Now, exec the specified image with arguments as the session leader.
+    # Recall, this replaces the image of this process.
+    try:
+        os.execvp(args[0], args)
+    except:
+        # Something went wrong. Put stderr back, and report the error.
+        os.dup2(bk, 2)
+        raise
+
+
+if __name__ == '__main__':
+    main()