TUI: don't let exceptions escape while handling readline key bindings

TUI: don't let exceptions escape while handling readline key bindings

I noticed that with:

 $ TERM=dumb ./gdb -q -nx
 <c-x,a>
 Cannot enable the TUI: terminal doesn't support cursor addressing [TERM=dumb]
 (gdb)

The next key the user types is silently eaten.

The problem is that we're throwing an exception while in a readline
callback that isn't prepared for that:

(top-gdb) bt
#0  tui_enable () at /home/pedro/gdb/mygit/build/../src/gdb/tui/tui.c:388
#1  0x000000000051f47b in tui_rl_switch_mode (notused1=1, notused2=1) at /home/pedro/gdb/mygit/build/../src/gdb/tui/tui.c:101
#2  0x0000000000768d6f in _rl_dispatch_subseq (key=1, map=0xd069c0 <emacs_ctlx_keymap>, got_subseq=0) at /home/pedro/gdb/mygit/build/../src/readline/readline.c:774
#3  0x0000000000768acb in _rl_dispatch_callback (cxt=0x1ce6190) at /home/pedro/gdb/mygit/build/../src/readline/readline.c:686
#4  0x000000000078120b in rl_callback_read_char () at /home/pedro/gdb/mygit/build/../src/readline/callback.c:170
#5  0x0000000000619445 in rl_callback_read_char_wrapper (client_data=0x0) at /home/pedro/gdb/mygit/build/../src/gdb/event-top.c:166
#6  0x000000000061981b in stdin_event_handler (error=0, client_data=0x0) at /home/pedro/gdb/mygit/build/../src/gdb/event-top.c:372
#7  0x000000000061840e in handle_file_event (data=...) at /home/pedro/gdb/mygit/build/../src/gdb/event-loop.c:762
#8  0x00000000006178f5 in process_event () at /home/pedro/gdb/mygit/build/../src/gdb/event-loop.c:339
#9  0x00000000006179bc in gdb_do_one_event () at /home/pedro/gdb/mygit/build/../src/gdb/event-loop.c:403
#10 0x0000000000617a0c in start_event_loop () at /home/pedro/gdb/mygit/build/../src/gdb/event-loop.c:428

Here, in _rl_dispatch_subseq:

769
770               rl_executing_keymap = map;
771
772               rl_dispatching = 1;
773               RL_SETSTATE(RL_STATE_DISPATCHING);
774               (*map[key].function)(rl_numeric_arg * rl_arg_sign, key);
775               RL_UNSETSTATE(RL_STATE_DISPATCHING);
776               rl_dispatching = 0;
777
778               /* If we have input pending, then the last command was a prefix
779                  command.  Don't change the state of rl_last_func.  Otherwise,

GDB is called from line 774, but longjmp'ing at that point leaves
rl_dispatching and RL_STATE_DISPATCHING set.

Fix this by wrapping tui_rl_switch_mode in a TRY_CATCH.

gdb/
2014-10-29  Pedro Alves  <palves@redhat.com>

	* tui/tui.c (tui_rl_switch_mode): Wrap tui_enable/tui_disable in
	TRY_CATCH.