[PATCH 2/4]: Handle SIGINT under Python by raising KeyboardInterrupt

[Tom Tromey]

>>>>> "Yit" == Khoo Yit Phang <khooyp@cs.umd.edu> writes:

Yit> Doesn't throw_exception use a longjmp? Say that we're running inside
Yit> Python's interpreter, and an Ctrl-C occurs, causing handle_sigint to
Yit> be called. handle_sigint calls gdb_call_async_signal_handler
Yit> (sigint_token, immediate_quit), which directly calls
Yit> sigint_token-> proc which is async_request_quit, which in turn calls
Yit> quit (), which calls throw_exception which calls longjmp to the
Yit> nearest TRY_CATCH. At this point, we have no idea what the state of
Yit> Python's interpreter is, and could well easily mangle something since
Yit> the longjmp can occur at any point.

This can only happen if immediate_quit is set.  But, immediate_quit is
used rarely in gdb.  It is not really safe to use in most situations.

We do have an issue that there are a few "bad" uses of immediate_quit.
But we need to fix those anyhow, as SIGINTs delivered in those places
can currently cause all kinds of issues.

The code is kind of confusing because gdb_call_async_signal_handler
conditionally does its work:

  if (immediate_p)
    call_async_signal_handler (handler);
  else
    mark_async_signal_handler (handler);

immediate_p is just immediate_quit due to:

  gdb_call_async_signal_handler (sigint_token, immediate_quit);

Tom